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posted by - Updated Wednesday, 02 December 2015

Many questions regarding ALEXA are answered in the ALEXA User Manual. Information contained in the manual will not be duplicated here. These frequently asked questions (FAQ) were last updated on August 19, 2011 and supersede any earlier versions. Any directions given are always from the operator’s point of view.

Table of Contents

General Questions

Lens Questions

Exposure Questions

Power Questions

Working on the Set Questions

Remote Control Questions

Heat/Cold/Environmental Questions

Electronic Viewfinder Questions

Workflow Questions

SxS PRO Cards Questions

Quicktime/ProRes Questions

Audio Questions

 3D Questions

ARRIRAW Questions

Accessories Questions

Sensor / Image Processing Questions

Service Questions

Further Resources & Online Tools

General Questions
Table of Contents

What can I do to familiarize myself with ALEXA?

There are a number of steps you can take from the comfort of your own home.

For starters, we recommend the following:

1. Read this one page ALEXA Data Sheet.

2. Read this FAQ. Here we have collected and answered many questions that have been asked by your colleagues when they worked for the first time with ALEXA.

3. A lot of the information you may need on the set has been summarized in the ALEXA Pocket Guide, which can be downloaded.

4. The “ARRI Tech Talk” are short videos about ALEXA products and features. To familiarize yourself with ALEXA’s control panel you can use the ALEXA Camera Simulator.

5. The main course, with more in-depth information about ALEXA, should be this: ALEXA User Manual

6. Talk to your local rental house and play with an ALEXA when it is available, or, even better, shoot a test

What online tools do you have available for the ALEXA?

There are a number of online tools to make working with ALEXA easier and more powerful.

ALEXA Frame Line Composer – ALEXA has a number of default frame lines built-in for the most common aspect ratios. In addition, it is possible to create custom user frame lines. Those are kept as xml files and are loaded from the camera’s SD card. If you know how to edit xml files you can make any shape you like as a frame line. If you don’t want to edit xml files and download them to your computer. From there, you can copy them to the SD card.

LUT Generator – For viewing Log C images directly on the set and for color correcting in post, look up tables (LUTs) are used. While Log C images provide the greatest flexibility in post, viewing them directly on a regular monitor provides a washed out and desaturated image and will freak out the director. A LUT transforms the digital signal to show a color correct video signal for monitoring.

Typical applications of LUTs in combination with Log C images include creating previews of Log C images on the set, converting Log C images for dailies, converting Loc C images in the display path for color correction and, last but not least, a round trip conversion of Log C to linear data for VFX workflows.

Please note that the ARRI online LUT generator is not designed for creating ARRI Look Files, but rather Look Up Tables for third-party equipment.

Will there be a 4K ALEXA?

At ARRI we focus on providing the best image quality for cinematographers and high-end features, together with an efficient workflow. Achieving the highest K figure is of less importance. ALEXAs 3.5K sensor with 800 EI base sensitivity and well over 14 stops of exposure latitude produces gorgeous, cinematic images. Given that 4K digital workflows are still in their infancy, and that for the foreseeable future most productions will finish in 2K or HD, ALEXA is the perfect choice for production. Furthermore, the ascendance of 3D has resulted in a doubling of image data volumes which further complicates the effective storage, processing and movement of such data. So, for the foreseeable future, ALEXA is ideally suited for 2K or HD 2D and 3D workflows.

Can I update an ALEXA or ALEXA Plus to an ALEXA Studio?

No. The ALEXA Studio has a different housing, contains different electronics and requires different testing and calibration for its 4:3 sensor. Updating an ALEXA or ALEXA Plus would be prohibitively expensive, and so we do not offer it as an option.

Lens Questions
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Which lenses can I use with ALEXA?

All modern 35 format PL mount lenses can be used with ALEXA, ALEXA Plus and ALEXA M, including the Optimo DP zooms. However, the Optimo DP zooms are not compatible with ALEXA Studio.

Can I use anamorphic lenses with ALEXA?

Yes. You can use both traditional anamorphic lenses with a 2x squeeze factor as well as anamorphic lenses with a 1.3x squeeze factor with ALEXA cameras.

When using the ALEXA and ALEXA Plus cameras, which are capable of 16:9 but not 4:3 sensor mode, using the 1.3x anamorphic lenses will provide a slightly more efficient use of the sensor’s 16:9 aspect ratio and thus a slightly higher resolution and less noise in the final image. However, since ALEXA has a very sharp image and a very low noise level to begin with, the ‘conventional’ 2x squeeze anamorphic lenses work as well. In that case you need to crop the 16:9 (1.78:1) image in post to 1.195:1, before de-squeezing the image to 2.39:1.

When using the ALEXA M or ALEXA Studio, it is much better to use 4:3 sensor mode when shooting with anamorphic 2x squeeze factor lenses.

Anamorphic de-squeezing in the viewfinder and on the MON OUT is available as a software license key for purchase for the ALEXA and ALEXA Plus. It is always included in the ALEXA Studio. This feature will work for 2x and 1.3x anamorphic lenses.

Will there be a shading artifact with ALEXA?

No. Shading (or “portholing”) is an effect that occurs when a lens is used with light rays that are at a large angle to the optical axis and some of those rays get obstructed either by a micro lens and/or don’t reach into the little well each pixel is situated in.

ALEXA has relatively large pixels and any shading is much less prominent with larger pixels than it is with small pixels. Additionally, we have already tested the Master Primes, Ultra Primes, Lightweight Zoom LWZ-1 and the Alura Zooms, and found that their light rays have no steep angles (= a ‘near-telecentric’ design) that would cause shading with ALEXA’s sensor.

Exposure Questions
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Does ALEXA’s exposure latitude change with different Exposure Index (EI) settings?

No, it does not. Most digital cameras have the greatest exposure latitude at a specific EI setting (often called the ‘sweet spot’). Choosing an EI setting that is higher or lower than the optimal setting will result in a sometimes surprisingly large loss of exposure latitude. ALEXA is unique in that its exposure latitude of 14 stops stays constant from EI 160 to EI 3200.

What happens when I change ALEXA’s Exposure Index (EI) setting?

While ALEXA’s 14 stops of exposure latitude and unique highlight handling approaches that of film, there is one major difference between the way film and digital cameras behave: with digital cameras, a change in EI will shift how many stops are available above and below 18% grey – each EI step shifts the location of 18% grey.

As a shortcut, we have come up with the following method of writing ALEXA’s exposure index:

ALEXA Sensitivity

Values behind the exposure index are the number of stops above and below 18% grey. These values are for Log C. Rec 709 and DCI P3 have 0.5 stops fewer in the low end at EI 160, 0.4 stops fewer in the low end at EI 200 and 0.2 stops fewer in the low end at EI 400. Otherwise they are the same.

  Can I use traditional ND filters with ALEXA?

While traditional ND filters work great for film, for digital cameras we recommend the use of ND filters that have a built-in far-red cut-off. Such filters are available from a number of manufacturers, often called “ND filters with an IR-cut off”. A single filter that combines an ND and a far-red cut off generally yields better results and fewer reflections than a traditional ND filter stacked on top of a separate IR cut off filter.

And here a little background: Film is not very sensitive in the far-red portion of the spectrum, so there was no need for traditional ND filters to cut that part of the spectrum. Digital cameras, on the other hand, are more sensitive in the far-red portion of the spectrum. Digital cameras are designed to create great looking images when a certain combination of wavelengths, i.e. natural light, hits the sensor. When a traditional ND filter is used with a digital camera, the filter attenuates most of the visible spectrum, but lets lots of energy in the far-red spectrum through. This results in much more far-red in relation to the other wavelengths of light, and can lead to some black fabrics, especially synthetics, being recorded with a reddish/brown tint.

While the close match between ALEXA’s custom designed IR filter and the sensor’s spectral response makes this issue less critical in contrast to some other digital camera’s, it is in general a good idea to only use traditional film ND filters up to an ND 0.9.

Can the full exposure latitude of ALEXA be recorded as ProRes onto SxS PRO cards?

The short answer is: yes, the full exposure latitude of the ALEXA can be recorded as ProRes onto SxS cards. The long answer is this: The ALEXA sensor can capture 14 stops of exposure latitude. This image data is processed internally in a 16 bit format. Whenever this data is converted to an output, be it the 12 bit ARRIRAW, 10 bit HD-SDI, 12 bit ProRes 4444 or in any of the other 10 bit ProRes formats, the whole exposure range of the captured image is mapped from the 16 bit range into the respective target output range (see graphic). So while the range from brightest to darkest image content remains the same, what changes is the number of different lightness levels in between. A 12 bit image has more steps between the brightest and the darkest parts than a 10 bit image. If there are not enough steps between the brightest and the darkest part of the image, you will see banding artifacts, where, rather than seeing a gradual change in lightness, you will see distinct bands of lightness. 10 bit images usually have enough steps to avoid such artifacts. ALEXA Tone Range Mapping

I see some noise at low fps and wide open shutter. Is that normal?

ALEXA currently allows the setting of exposure times in excess of 1 second (i.e. 358° shutter at 0.75fps = 1.25 seconds exposure). To achieve optimum image quality at slow frame rates, the exposure time should be limited by selecting a shutter angle of 180 degrees or less.

Should I use the camera’s white balance settings or color correction filters?

Using the camera’s built-in white balance settings is almost always preferable to color correction filters in front of the lens. First, a color correction filter will take away light from all three colors, so all three will have to be amplified, which leads to more overall noise. Using the camera’s white balance setting instead will only amplify those color channels needed to achieve a neutral color balance. Second, all filters currently in the market have been designed for the spectral response of film. Since sensors have a different spectral response than film, you may get unexpected results.

What is the native color temperature of ALEXA’s sensor?

The short answer is that while ALEXA does not really have a ‘native’ color temperature, the point at which the lowest overall gain is applied to the red, green and blue pixels is at about 5600 degrees Kelvin, yielding the lowest possible noise in the image. However, since ALEXA has an amazingly low noise level anyway, the differences in noise between 3200K and 5600 K are so minimal as to not be of importance in most everyday shooting situations. So choosing the color temperature can be dictated by other factors, such as the cinematographer’s preference or the availability and/or cost of tungsten or daylight lighting instruments.

For the long answer, we have to start with the birds and the bees, or in our case, with celluloid and silver halide crystals. Film stocks are balanced for either a tungsten (3200 degrees Kelvin) or a daylight (5600 degrees Kelvin) light source. To achieve this, film manufacturers carefully tune the chemistry of the individual color layers. The goal is that a grey card filmed under the respective lighting conditions will also result in a neutral grey image after development. Thus each film stock has a given color temperature ‘baked-in’, which is sometimes also called the ‘native’ color temperature of that film stock. If you need a different color temperature, you change film stocks.

The way light is converted to an image is different for film and image capture sensors. In order to display a grey card as grey, digital cameras have to carefully balance the red, green and blue (RGB) signals. The response of a digital camera to incoming light of different colors is determined by the response behavior of the filter pack (IR, low pass, UV), the photocell, the Bayer mask inks and the image processing. Even though the properties of the filter pack, photocell and Bayer mask inks are chosen with the best color balance in mind, there are other factors that also influence the color balance of the signal coming from the sensor, including an optimization for highest sensitivity, widest dynamic range and lowest noise. The proper balance between all those requirements is not only difficult to achieve, but also one of the factors that will yield a great looking digital image and differentiate the various models of digital cameras.

Since one can neither create a sensor for each color temperature, nor change them if one could, digital cameras have to cover a variety of color temperatures with one sensor. For any given color temperature, a sensor will deliver an unequal amount of red (R), green (G) and blue (B) signal. In order to balance the three colors for different color temperatures, digital camera manufacturers use different amplification settings for red and blue, while keeping green unamplified.

Let’s look at the actual settings ALEXA uses to illustrate this.

R – 1.28x
G – 1.00x
B – 2.07x

Shooting the same chart, but now lit with a daylight source (5600 K), will put more blue and less red light on the sensor. So we can apply less amplification to the signal from the blue pixels but need a little more amplification for the signal from the red pixels:

R – 1.65x
G – 1.00x
B – 1.37x

So, for tungsten ALEXA uses a little more amplification in the blue channel, and for daylight a little more in the red. And for those who are still reading and want more: even though the red and blue amplification are about equal at 5,000 K, daylight (5.600 K) has the mathematically lowest overall noise gain, measured as the square root of the sum of the squared gains. Anyone who has not had enough by now can open their Richard Feynman textbook on quantum mechanics on page 3,421 and read quietly by themselves. :-)

Power Questions
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What are ALEXA’s power inputs?

ALEXA has three possible power inputs: the BAT connector, the battery adapter back and the battery adapter top. There are different battery adapters available for either V-lock or Gold mount batteries. If more than one power source is available to ALEXA, she will automatically pick the power source with the highest voltage. Power sources can be hot plugged (attached and removed without powering the camera down first).

What are the minimum and maximum power voltages for ALEXA?

ALEXA will accept any input from 10.5 to 34.0 V DC on any power input. Most 14.4, 24 and 26 Volt batteries and power supplies will work fine, as long as they can supply at least 100 W. While most 12 V batteries will work, they can quickly discharge below the 10.5 V limit and thus are not recommended. While most 30 V batteries will work, they will supply above the 34.0 V limit when fully charged and thus are also not recommended.

What is ALEXA’s power draw?

The power draw of the ALEXA camera and viewfinder is about 85 W. The power supply should deliver an output of more than 90 W to power the camera and viewfinder sufficiently. Additional accessories such as lens motors will add an additional power draw. Except for the ARRI HDM-7, which draws relatively little power, it is recommended to power on-board monitors from an external source. Please note that using a 24 V power source is more efficient than using a 14.4 V source, as ALEXA uses 24 V internally.

What kind of on-board batteries are compatible with ALEXA?

Any battery that fits to a Gold mount or V-lock can in principle be used on the respective battery adapter of ALEXA. For all of those batteries, ALEXA can measure and display the battery’s voltage.

Please note that Anton/Bauer recommends against using the following battery types with ALEXA since they would have short run-times and are not rated to handle such power requirements, which could reduce their life expectancy: ProPac 14, Digital ProPac 14, TrimPac 14, Digital TrimPac 14, HyTRON 50, DIONIC 90. Also note that the PAG-L190e is so wide that it obscures access to the connectors on ALEXA’s back/right side.

For Anton/Bauer and IDX batteries ALEXA can communicate directly with the battery and display the battery capacity in percentage, which is a more accurate measure of how much longer the battery will last, especially with Lithium-ion batteries. We are working on increasing the number of batteries that can communicate with ALEXA.

Why are there no power tabs on the ALEXA battery adapters?

Most on-board batteries are capable of powering ALEXA and the accessories attached to ALEXA. Putting any further drain on them can result in significantly shortened battery life and problems. This is why we consciously did not put a power tab on the ALEXA battery adapter.

Why does the battery display sometime switch from percent to voltage?

ALEXA can actively communicate with some on-board batteries (currently Anton Bauer and IDX) in order to display the battery capacity, which is a more accurate indication of remaining battery life than the default voltage indication. However, as long as a heavy accessory power load is applied to the camera, ALEXA can only display voltage, not capacity. As soon as the load is reduced, the indication will show capacity again. This issue only influences how the battery strength is displayed and has no influence on any other camera functions.

Please note that when the battery strength is displayed by voltage, the camera will display the battery low warning based on the battery low warning limit set in the MENU > SYSTEM > POWER menu, and not based on the battery capacity as communicated by the battery.

When do I get battery warnings and battery errors and what do they mean?

We distinguish between two types of batteries and two low power indications. Smart batteries can communicate with the camera, and normal batteries cannot. When the battery runs low, the camera issues a power warning, and when it runs even lower a power error. Once the camera reaches the power shut off level of 10.5 Volt, it will turn off no matter what batteries are used.

Power Indications for Normal Batteries

The voltage level at which a power warning occurs is 12 V by default, but can be set in MENU > SYSTEM > POWER to another value. A power warning will be indicated in the camera display by a white “i” icon appearing on the left side and by a blinking BAT1 or BAT 2. More information on the warning can be had by pushing the INFO button to the left of this “i” icon. If the camera status lines are turned on for the viewfinder and/or for the MON OUT output, they will also show a white “i” symbol. During a power warning the camera will continue to function normally.

If the voltage falls to 10% below the set warning level (i.e. 10.8 V assuming a power warning level of 12 V), the camera gives a power error. A power error will be indicated in the camera display by a red “i” icon appearing on the left side and by a blinking BAT1 or BAT 2. More information on the warning can be had by pushing the INFO button to the left of this “i” icon. If the camera status lines are turned on for the viewfinder and/or for the MON OUT output, they will also show a red “i” symbol. A power error changes the camera’s behavior. If the camera is recording to SxS PRO cards, it will attempt to continue recording until it reaches the shut off level. If it is in standby, it will not allow you to start recording to SxS PRO cards, but will stay powered on until it reaches the shut off level.

Power Indications for Smart Batteries

The voltage level at which a power warning occurs is 10% of the battery’s full capacity and cannot be changed manually. A power warning will be indicated in the camera display by a white “i” icon appearing on the left side and by a blinking BAT1 or BAT 2. More information on the warning can be had by pushing the INFO button to the left of this “i” icon. If the camera status lines are turned on for the viewfinder and/or for the MON OUT output, they will also show a white “i” symbol. During a power warning the camera will continue to function normally.

If the voltage falls to 5% of the battery’s full capacity, the camera gives a power error. A power error will be indicated in the camera display by a red “i” icon appearing on the left side and by a blinking BAT1 or BAT 2. More information on the warning can be had by pushing the INFO button to the left of this “i” icon. If the camera status lines are turned on for the viewfinder and/or for the MON OUT output, they will also show a red “i” symbol. A power error changes the camera’s behavior. If the camera is recording to SxS PRO cards, it will attempt to continue recording until it reaches the shut off level. If it is in standby, it will not allow you to start recording to SxS PRO cards, but will stay powered on until it reaches the shut off level.

Working on the Set Questions
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How can I mount third party recorders onto ALEXA?

There are many 3/8-16 UNC attachment points on ALEXA, and a number of M4 attachment points on the top surface of the camera for attaching third party recorders. Many recorder manufacturers already have brackets in their program that attach to the top of ALEXA and to their respective on-board recorders.

Please note that the Center Camera Handle CCH-1 (K2.72007.0) cannot be used together with a top mounted on-board recorder. Instead, use the Side Camera Handle SCH-1 (K2.72016.0) together with the Adjustable Center Grip Tall (ACG-2, K2.72022.0).

Why is there no display on ALEXA’s left side? 

ALEXA has no display on the camera left side since there is no good place for it. ALEXA is smaller than a film camera and has no ‘chin’ that would house a mirror shutter, so there is no place that would not be covered by the operator. Thus any display would be inaccessible to the assistant while shooting.

However, it is still possible to change camera settings from the left side. The most important buttons are available to the assistant and the operator can monitor and change the most important settings in the Electronic Viewfinder EVF 1. Additionally, the Remote Control RCU-4 provides a complete copy of the right side display and can be attached anywhere near or far from the camera.

Can I connect the headphones while the camera is running?

No. Connecting the headphones while the camera is running can, in rare cases in environments with heavy static electricity, lead to a brief shut-down of the audio circuit. The audio circuit will reboot automatically, but some audio will not be recorded. Always attach and detach the headphones connector while the camera is not recording.

Why does the timecode on ALEXA’s display show a delay?

The timecode displayed in the camera‘s display shows some delay in reference to the actual timecode signal. The display is meant as a reference to check if the timecode values are correct, but is by no means frame accurate. Don‘t use the display to check Timecode frame accuracy. The recorded timecode is, of course, frame accurate.

Can I use reel numbers above 999?

No. ALEXA’s reel counting system only works up to 999 reels. 

Does the MON OUT output have the same image quality as REC OUT?

Yes, the MON OUT output has the same image quality as the two REC OUT outputs. However, there are a couple of differences and extra options that you should be aware of:

MON OUT does not have all the signal formatting options that REC OUT has; MON OUT runs only at 4:2:2 (single link 1.5G) @ 23.976, 24, 25, 29.97 and 30 fps. Second, on MON OUT you can superimpose frame lines and camera information, and shrink the image (surround view) to see more than what will be recorded. These are all features that are useful for monitoring the image, but that you most likely will not want on a master tape. Thus they are only available in the viewfinder and on the MON OUT output, but not on the REC OUT output.

So, if all you want is 4:2:2 and you turn frame lines, camera info and surround view off, the signal from MON OUT has the same quality as a 4:2:2 signal from REC OUT.

Will I get rolling shutter artifacts when shooting with ALEXA?

That depends. ALEXA uses a CMOS sensor with a rolling shutter. The pixels are read out from the sensor sequentially, starting at the top left of the image and then read line by line until the bottom right is reached. It is possible that a fast event, like a photographer’s flash, is over when only part of the sensor has been read out, leading to a frame with only the top part exposed by the flash. It is also possible that straight vertical lines will be slightly bend during a fast pan (an effect sometimes called “skew”). However, ALEXA’s read-out speed is very fast, so this effect is not very prominent.

The ALEXA Studio can be used in electronic shutter mode, in which case it functions like all other ALEXAs and like described above, but it can also be used in rotating mirror shutter mode, in which case a physical, half moon shaped mirror (see image) rotates in front of the sensor. This mirror shutter has the function of a global shutter. While the light strikes the sensor, the pixels are exposed and accumulate a charge. When the mirror fully covers the sensor, the charge is read out. This eliminates any rolling shutter artifact and works just like a film camera does in terms of exposure.

Are the recommended panning speeds for ALEXA the same as for 35 mm film cameras?

Yes. Our tests comparing film cameras, ALEXAs with an electronic shutter and ALEXAs with a mirror shutter have shown very little difference between them.

Can I run ALEXA upside down?

Yes, it is no problem to run ALEXA upside down. The fan will still work and cool the camera sufficiently.

Image compare does not seem to work. Why?

When one of the anamorphic de- squeeze options or RETURN IN is on, it is not possible to load an image for the compare function. If the camera is instructed to load an image, the ‘Loading Image’ screen will be visible until any key is pushed.

Why are the names for framelines sometimes not fully displayed?

A number of files, like frameline files and ARRI Look Files, can be freely named when they are created on a computer. We recommend to keep the names short and succinct, as there is a limit to how many charcaters the ALEXA can display.

Is it a problem flying in an airplane with a digital camera?

With the kind permission of The Film & Digital Times, here is the answer from Stephen Stough, Cinematographer, Producer, and President of Tradecraft Films, regarding sensors at high altitude, and the perils of shipping digital cameras by air. “In general, a short exposure of camera equipment at altitude within the atmosphere is not going to cause any measurable damage, even when powered on, but much less so if powered off in transit. It is true that heavy particles, such as heavy (fast) protons will leave tracks up to 1 mm long through glass, and eventually glass will turn translucent, metals become embrittled and so forth. But, that takes tens of years in space, and probably hundreds of years at the altitudes at which aircraft fly.

It is always possible that a heavy ionization track will damage the insulator(oxide) at a pixel site to the degree that when the sensor is powered on, the resulting short circuit current would flood that pixel site, and burn it out. The possibility isn’t zero. It would take some time to calculate the possibility in a real situation (where the sensor is buried inside an airframe inside a shipping case and inside a camera). If it were my camera, I wouldn’t give it a second thought because I think the possibility in a few hundred hours of aircraft flight to be vanishingly small and economically not worth worrying about. That is, the cost of taking extra protective measures would probably never pay off in terms of an actual lost-pixel event being avoided.”

Remote Control Questions
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How can I remotely control ALEXA?

Basic remote control of the regular ALEXA (non Plus) can be achieved with the cabled RS-4 switch, or with the ARRI Wireless Remote System (WRS). When using the WRS, a UMC-3A or UMC-3 must be attached to the camera so the Wireless Main Unit WMU-3 or Wireless Compact Unit WCU-3 can remotely control the REC function.

The UMC can be connected to the EXT connector on ALEXA with the UMC Connection Cable (0.80m/2.6ft) K-UMC3-ALEXA, K2.65239.0. This configuration allows remote REC and supplies basic status information to be displayed on the WCU-3. Alternatively, the UMC can be connected to the RS connector on ALEXA with the cable K-UMC3-RS (KC-98S, K2.65014.0, 0.53m/1.7 feet). This configuration allows only remote REC; it does not supply remote status information to the WCU-3.

Please note that the WMU-3 and the WCU-3 will show a green illuminated LED when recording is in progress, and no illumination when the camera is in standby or off. This is different from the behavior of the ALEXA RUN LED, which will be green in standby and red during recording.

Essentially the same applies when using the ALEXA Plus, except when using the ARRI Wireless Remote System, the UMC-3 or UMC-3A is not necessary, as its functions are built-into the ALEXA Plus.

The Remote Control Unit RCU-4 supplies complete cabled remote control of ALEXA and ALEXA Plus, including the ability to change all settings.

What are the best browsers to use with ALEXA’s remote control web page? 

Our tests have shown best results with Firefox, Chroma and Safari. Internet Explorer is not compatible with some of the Web 2.0 technologies used in the ALEXA web bowser.

Heat/Cold/Environmental Questions
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What is Tropical sensor temperature? Will it make the camera quieter?

The temperature of ALEXA’s sensor is being actively maintained at a constant 35 degrees Celsius. When shooting in very hot and humid conditions, in rare cases it is possible for condensation to build on the inside of the filter pack in front of the sensor. In this case the sensor can be switched to ‘Tropical temperature’ in the SYSTEM > SENSOR menu, which will heat the sensor to 40 degrees. Running the sensor at 40 degrees will only affect condensation. It will not affect the image quality during normal operation, nor will it reduce the camera’s sound. However, since it uses more power we recommend to run the sensor at its standard temperature mode by default. Tropical mode will be indicated by a palm tree icon in the camera right display, and by the ‘i’ information icon in the viewfinder.

Why does the ALEXA at first show the sensor to be too hot when started in very cold temperatures? 

When ALEXA is powered up in very cold temperatures the sensor temperature regulating circuit can take a couple of minutes to settle on the proper temperature. During that time you might get warnings that the sensor is too hot. In cold temperatures it is always recommended to let the camera come up to a proper working temperature for a couple of minutes before recording.

What should I consider when shooting in extremely hot temperatures? 

In most cases, the camera should be run in ‘Regular’ fan mode, which achieves silent running of 20 db(A) at temperatures of up to +30 degrees Celsius (+86 degrees Fahrenheit). This has proven sufficient for most shooting situations. Once the ambient temperature, and thus the camera’s internal temperature, increases, the camera will slowly increase the fan speed, and thus fan noise, to assure proper cooling of the electronics. This works the same in all operating modes: Standby, Record and Playback.

In the rare case that fan noise becomes objectionable because of higher ambient temperatures, it is possible to switch the fan into ‘Rec low’ mode. As long as the ambient temperature remains below +30 degrees Celsius (+86 degrees Fahrenheit), ‘Rec Low’ mode is no different from ‘Regular’ mode. However, once the camera’s internal temperature reaches a certain threshold (which is not directly related to ambient temperature, but approximately around an ambient +30 degrees Celsius (+86 degrees Fahrenheit)), the fan will run fast during Standby and Playback to pre-cool the camera, and will run slowly and silently during recording for as long as possible. If, while recording, the camera reaches its temperature limit, it will slowly start increasing the fan speed to cool its electronics. When the camera is set to ‘Rec low’ fan mode it will allow a higher internal temperature in order to stretch the silent running as long as possible, which means that the camera housing can be warmer to the touch than in ‘Regular’ mode.

Since ‘Rec Low’ increases the camera’s noise in hot environments during Standby and Playback, we recommend ‘Rec low’ mode only when the fan noise becomes objectionable in very hot ambient temperatures.

Note: noise can also be caused by a worn out fan, and can be easily switched to a newer, more silent fan.

What should I consider when shooting in extremely cold temperatures?

While ALEXA is officially rated to -20° C / -4° F (@ 95% humidity max, non condensing), we have had a number of customers who have worked with ALEXA at significantly lower temperatures, without any heating barneys and without any problems. However, below  -20° C / -4° F any humidity in the air or from the human breath will quickly condense on the eyepiece and even freeze there, obscuring the view, so an eyepiece heater is recommended. Also, keeping batteries warm and charged is critical, as batteries loose their  power at cold temperature.

Electronic Viewfinder Questions
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Is there a way to avoid the stuttering effect in the viewfinder? 

Yes. In the camera’s menu, go to MENU > MONITORING > ELECTRONIC VIEWFINDER and turn ‘Smooth mode’ to ‘on’.

Smooth Mode off: A certain amount of stuttering, which can be observed especially during quick pans, is inherent to all low frame rate progressive image displays. The sharpness, contrast and relatively large image size of the EVF-1 make this effect even more apparent. The effect is much less noticeable when panning within the normally accepted maximum panning speeds (which is why some operators prefer to leave Smooth Mode off), and when following an object or person in frame. It may also be helpful to note that the effect will generally be much more apparent in the viewfinder than on separate monitors or projection, so represents a ‘worst case scenario’.

Smooth Mode on: The sensor will run at twice the set frame rate and the shutter will be at twice the set shutter angle. So if you have the camera set to 24 fps and 180° with Smooth Mode on, the sensor will run at 48 fps and 358° (Yes, it should be 360° but the sensor is only capable of 358°, and our tests have shown that this slight discrepancy does not make a difference). Every frame will be sent to the viewfinder, which makes the image impression in the viewfinder smoother. Only every other frame will be sent to further processing and recording, so you actually only record the 24 fps/180°. This is the reason why Smooth Mode only works up to half the maximum frame rate and half the maximum shutter angle. Smooth Mode also costs about 7W more power.

What do the colors of the false color exposure check mean? 

The false color exposure check for the viewfinder and/or MON OUT changes the image to black and white and certain signal levels are indicated by a specific color.

What is the false color exposure check based on? 

The false color exposure check is based on the color processing set for the respective output signal path. So if you have the viewfinder set to Rec 709, the false color exposure check in the viewfinder will be based on the Rec 709 image. If you have the MON OUT at the same time set to Log C, the false color exposure check for MON OUT will be based on Log C.

Why do the ZOOM and EXP buttons behave differently now?

The ZOOM and EXP buttons on the viewfinder used to be momentary buttons, which means that their functions were activated as long as they were pushed. By popular demand, they are both latching buttons from SUP 4.0 on. This means each one has to be pushed once to turn the function on, and then again to turn the function off. Please note that when zoomed in, the image will have a thick orange border to clearly indicate the zoomed in state.

Do I need a heated eyecup for ALEXA?

No. The viewfinder itself generates a certain amount of heat, which is transferred to the eyepiece in a controlled manner to avoid fogging in most shooting situations. Only in extremely cold situations, i.e. as encountered in the arctic, may a heated eyecup be of use.

Can the ALEXA viewfinder stretch my anamorphic image to the proper aspect ratio?

Yes. Anamorphic de-squeezing in the electronic viewfinder and on the MON OUT is available as a software license key for purchase and will perform either a 2x or a 1.3x de-squeeze. The ALEXA Studio’s optical viewfinder has a 2x de-squeeze element built-in, which can be replaced with a 1.3x de-squeeze module.

Why would I want to use an electronic viewfinder with the ALEXA Studio?

While an optical viewfinder will provide the best viewing experience, there are three situations where an electronic viewfinder or an on-board monitor have advantages. First, the mirror shutter of the ALEXA Studio supports speeds up to 60 fps. If you want to shoot faster in high speed mode, you must switch the mirror shutter off and thus will loose the use of the optical viewfinder. Second, if an open shutter angle larger than 180º is desired the mirror shutter must be turned off and the electronic rolling shutter must be used instead. And third, when shooting in extremely dark situations the electronic viewfinder will be able to show a brighter image.

Workflow Questions
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What kind of outputs does ALEXA have? 

ALEXA is unique in that it can simultaneously record an HD ProRes file onto onboard SxS PRO cards, output ARRIRAW and output HD-SDI video. The different output options can be seen in the graphic below. Each split in the lines is an “or” option.

What is the difference between Log C (film matrix off), Loc C (film matrix on), Rec 709 and DCI P3?

Aside from the ARRIRAW output, which contains no color processing, ALEXA can output images with four different color processing methods (commonly called ‘gamma’) applied. Thus ALEXA can provide the appropriate image format for a wide range of workflows from feature films to television.

Log C (film matrix off) is a Log C signal with a wide gamut color space. This option provides great flexibility in color grading, as it preserves the most color information in the recorded image.However, you should be aware that Log C is an intermediate color format and not designed as a display standard. Viewed on a regular video monitor, Log C images look flat and desaturated. When using Log C images, color grading becomes an obligatory post production step and for proper previewing, creation of dailies or editing proxies it is necessary to use Look Up Tables (LUT). LUTs for ALEXA can be downloaded from 
www.arridigital.com/technical/luts. For any further help with LUTs, contact 

Log C (film matrix on) applies a color matrix that makes the resulting image resemble a film negative scanned on an ARRISCAN. While this option somewhat reduces the color gamut in contrast to Log C (film matrix off), it provides an easy and fast way for colorists who are used to scanned negative, thus speeding up color grading. It is also a great option when combining ALEXA images with film originated images. The same caveats as for Log C (film matrix off) also apply.

The same caveats as for Log C (film matrix off) also apply.

Rec 709 is the output format for a traditional television workflow. ‘Rec 709’ is short for the International Telecommunication Union’s ITU-R Recommendation BT.709. Since Rec 709 is the international standard for displaying images on video monitors, Look Up Tables (LUTs) are not necessary to show these images on monitors or to create dailies or editing proxies. Additionally, Rec 709 images can be easily processed by most HD video postproduction gear in real time. While providing somewhat reduced choices in color grading, Rec 709 still maintains ALEXA’s wide exposure latitude, cinematic look and natural color rendition and offers the fastest workflow when using an HD video based infrastructure.

DCI P3 is suited for DCI P3 (also known as SMPTE 431-2) compliant displays. Those are primarily digital cinema projectors, but an increasing number of LCD displays supports DCI P3 as well. DCI P3 has a similar tone mapping to Rec 709 but a wider color gamut that is designed to approximate the color gamut of print film. If you have a DCI P3 compliant monitor on the set or can see a DCI P3 compliant projection, this will give you a good idea what your images will look like in the digital cinema without having to use Look Up Tables.

Can I use Log C, Rec 709 or DCI P3 with QuickTime/ProRes Recording?

Yes. However, when using Log C gamma we recommend ProRes 4444 for best results. While Rec 709 and DCI P3 gamma can be used equally well with all ProRes codecs, Log C can in some situations lead to banding when using a ProRes codec other than ProRes 4444.

Can I create a custom look for my ALEXA images?

Yes. As of Software Update Packet 4.0 it is possible to apply a customized look to all ALEXA outputs (EVF-1, MON OUT, REC OUT and/or SxS cards) through an ARRI Look File. Look files alter the way the camera image is converted to video color spaces. They can be activated to all image paths of the camera that are set to either Rec 709 or DCI P3. ARRI Look Files are editable XML files that contain a number of parameters including the ASC CDL primitives slope, offset and power.

ARRI Look Files can be created with a free Mac application called the ARRI Look Creator.

Once created, ARRI Look Files can be loaded from the SD card and stored in the camera. One look file can be selected at a time. This look file can be applied to the different image paths individually. So it is possible, for instance, to record a clean Log C image onto the SxS PRO card while outputting a Rec 709 image with a look applied on the MON OUT output. However, as soon as a look file gets applied to any output, the data of the look file is stored in the metadata of the QuickTime/ProRes clips and embedded in the HD-SDI metadata (for video and ARRIRAW).

Please note that the ARRI online LUT Generator is not designed for creating ARRI Look Files, but rather Look Up Tables for third party equipmnet.

Can I combine ALEXA’s Log C with S-Log material?

Yes. It is relatively easy to use a 1D LUT to convert ALEXA’s Log C material to S-Log or vice versa. LUTs for ALEXA can be created with the LUT Generator.

Will there be an F-Log or S-Log output option for ALEXA?

No. We currently have no plans to incorporate F-Log or S-Log. When working in a film-style post workflow, we feel that the Log C output option provides the best results.

What do I do if I need 720p content?

ALEXA does not produce 720p images. However, shooting 1080p allows you to sell your program to all countries that have chosen 1080p, and it can easily be down-converted to 720p.

SxS PRO Cards Questions
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Does ALEXA support other SxS cards in addition to the Sony SxS PRO cards?

No, ALEXA only supports Sony SxS PRO cards because that is the only solution with sufficient and reliable data writing rates. ALEXA does not support Sony SxS-1 cards, third party SxS cards, the SONY MEAD-MS01 Memory Stick Adaptor or third party adapters.

SxS PRO cards are professional grade memory cards. Their environmental robustness, high data rates, exceptional reliability and small size make them the perfect in-camera recording medium for the ALEXA family of cameras. The use of high end memory technology assures that the cards maintain their high data rate during their entire life.

Are 64 GB SxS PRO cards compatible with all ALEXA SUPs? 

64 GB SxS PRO cards will work fine with ALEXA SUP 4.0 and later but are not officially supported by SUP 3.1 or earlier.

How accurate is the remaining time display for SxS PRO cards?

The time displayed by ALEXA is based on the maximum possible data rate for a given codec at a given frame rate. Since the Apple ProRes codecs are variable bit rate codecs, the remaining time depends on image content, and will usually be longer than the time indicated. Please note that the estimation is updated in short intervals and the closer the card gets to be full the more accurate the estimation will be.

How can I switch to the other SxS PRO card when ALEXA is inaccessible? 

If you don’t have a RCU-4, record on card 1 until it is full. When the card is full, ALEXA will stop recording. When you then press REC again, the camera will automatically start recording onto the second card. If the second card then also fills up, ALEXA is smart enough to NOT switch back to card 1, so you have to exchange cards.

If you do have a RCU-4, you can switch which card you record to by assigning one of the USER buttons to the ‘Toggle SxS’ command.

How long will it take to format a 32 GB SxS PRO card in ALEXA? 

Formatting a 32 GB SxS PRO card takes 7 seconds. For ALEXA recording, the cards can only be formatted inside the ALEXA camera.

Can I use an SxS PRO card that has been formatted with a previous camera software?

No. You should only use cards that have been formatted with the same camera software version as the camera has you will be using

How long will it take to copy an SxS PRO card to a computer?

It takes about 7 minutes to copy a full 32 GB SxS PRO card or a full 64 GB SxS PRO card to a 17″ MacBook Pro laptop. The 64 GB card takes as long as the 32 GB card because the 64 GB card is capable of transferring files at over twice the data rate of the 32 GB card. If the card is not completely full, it will take less time.

Why does ALEXA not show the SxS PRO data rate anymore after formatting in SUP 5.0?

In order to save time during the formatting/erasing process, ALEXA does neither measure nor display the card’s maximum data rate after formatting anymore. However, ALEXA does display the maximum fps possible with the currently selected codec.

Quicktime/ProRes Questions
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What is the difference between the five Apple ProRes codes?

See ProRes Codes Overview.  

Can I view ALEXA ProRes clips on an AJA Ki Pro?

ProRes QuickTime files recorded by ALEXA do not show up on a Ki Pro if copied directly from SxS PRO card to the Ki Pro’s hard drive. After re-saving the files from another program such as Final Cut Pro (FCP) the clips can be played back on the Ki Pro.

I interrupted a  ProRes/SxS recording. What now? 

If a recording has been interrupted, for instance by a power cut or by removing the card without stopping the recording, the card should be backed up and reformatted before recording onto it again. The content of the card is readable, but the file system may have been compromised.

Why is ProRes always set to legal range?

Apple specifies that ProRes should be legal range. Our tests have shown that an extended range ProRes file can result in clipping in some Apple programs. However, the difference between legal and extended coding are essentially academic, and will not have any effect on any real world images. An image encoded in 10 bit legal range has a code value range from 64 to 940 (876 code values), and a 10 bit extended range signal has a code value range from 4 to 1019 (1015 code values). Contrary to popular belief, extended range encoding does not provide a higher dynamic range. It is only the quantization (the number of lightness steps between the darkest and brightest image parts) that is increased by a marginal amount (about 0.2 bits).

Why does Final Cut Pro warn that an ALEXA ProRes file is not optimized for real-time playback?

If a QuickTime clip that uses the ProRes codec begins with dark frames, FCP may display a warning dialog saying that the clip is not optimized for real-time playback. This is a false warning that can occur with any ProRes clip, not just those from ALEXA.

Audio Questions
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Is Alexa audio compressed?  

No, since audio has such low data rates in comparison to images, it is recorded uncompressed on the SxS PRO cards, and embedded uncompressed into the HD-SDI data stream.

3D Questions
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What are ALEXA’s advantages for 3D shoots?

ALEXA is a very compact and high performance camera, integrating easily into 3D rigs and producing remarkable 3D images. The high base sensitivity of ALEXA helps with 3D mirror rigs, as the mirror always takes some of the light. The wide exposure latitude helps to convey a more realistic and natural image, as clipping artifacts can be very detrimental to the viewer’s stereoscopic impression. The physical relationship of sensor position to camera mounting points is exactly the same on every ALEXA, making it easy to integrate ALEXAs into 3D rigs and assuring an easy replacement of one ALEXA for another on 3D rigs.

Cinematographers and high-end 3D solution providers have confirmed, from personal experience on ALEXA 3D projects, that the quality of 3D footage captured by ALEXA is simply stunning. From Software Update Packet 2.1 on, ALEXA has been capable of precise 3D synchronization of sensor, HD output, timecode and camera settings. To use these features, the ALEXA 3D Cable Set (K0.71032.0) is necessary.

Is there anything to pay attention to when using 3D lens sync?

Yes. When using two lenses on two ALEXA Plus cameras with 3D sync and 3D lens sync (i.e. the ARRI WRS or cmotion cvolution system is used to control the Master lens while the Slave lens follows), the lens with the larger focus read out at its mechanical close focus end stop must be on the Master camera.

In order to find out which lens has the larger focus read out:

Place each lens on an ALEXA Plus and look at the focus value on the LDS screen of the cameras display (WRS button > LENS DATA).

Turn the lens to its mechanical close focus end stop. Note the number that is displayed for focus.

The lens with the larger number must be on the Master camera.

If the lenses are reversed it is possible for the Master lens to reach a close focus value that the Slave lens cannot reach, and thus the Slave lens would be out of focus as long as the master is in that range.

ARRIRAW Questions
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What are the advantages of ARRIRAW?

ARRIRAW is the highest quality recording format when shooting with ALEXA, storing the full 2880 x 1620 pixels of raw, unprocessed 12 bit log Bayer data delivered by the sensor. Any steps that are necessary to create a full color image in a given resolution will be performed in post. This provides ARRIRAW advantages in terms of achievable resolution, post production flexibility and archivability.

When shooting for a 2K post workflow, recording ARRIRAW at 2880 x 1620 pixels and down-converting in post to a 2K image shows visibly better resolution than shooting in 1920 x 1080 HD and up-converting to 2K. This resolution difference is even more pronounced when special effects are involved: the ARRIRAW files can be reconstructed to a 2880 x 1620 full color image for special effects, and only be down-converted to 2K after the effects have been applied.

Many processing steps that are irreversibly ‘baked-into’ the ProRes or HD-SDI image on the set are not applied to the ARRIRAW files (de-bayering, downscaling, white balance, exposure index, gamma). Those processing steps will be performed in post, where there is more time and where they can be reversed at any time by going back to the original ARRIRAW files. Thus ARRIRAW provides more flexibility in post, including the flexibility to apply different vendor’s image reconstruction algorithms.

Since the ARRIRAW files are uncompressed and unencrypted, they can be archived and easily reconstructed into beautiful full color images at any point in the future. Technology unrelentingly advances, and so better image reconstruction algorithms are expected to be available in the future, where they can create an even better image from archived ARRIRAW files. This is analogous to film negative, which has been yielding better and better images with each new generation of telecines and scanners.

How is ALEXA ARRIRAW different from D-21 ARRIRAW?

D-21 ARRIRAW has the white balance baked in, since back in 2002 we felt that it would be closer to the way film negative behaves. The D-21 EI setting is not baked in. The 2880 x 2160 pixel images (4:3 aspect ratio) are transported as 12 bit linear data.

The ALEXA ARRIRAW file format has neither the white balance nor the EI setting baked in. However, both white balance and EI that are set in the ALEXA are stored in the ARRIRAW header as metadata. This metadata also includes other information like the green/magenta shift value (CC) that has been set in the camera. The 2880 x 1620 pixel images (16:9 aspect ratio) are transported as 12 bit log data, since this is a better way to transport ALEXA’s wide dynamic range.

Both file formats can be transported via ARRIRAW T-link. Recorders and post tools will be able to distinguish between D-21 and ALEXA ARRIRAW based on the metadata, so the whole thing is transparent to the user.

Accessories Questions
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What kind of bridge plates can I use with ALEXA and ALEXA Plus?

There are three different methods to attach ALEXA or ALEXA Plus to a bridge plate.

Each ALEXA or ALEXA Plus comes with a Wedge Adapter WA-1 attached to the bottom of the front foot. This allows the camera to be attached to an ARRI, SONY or Panasonic video-style quick release plate, and is a great choice for those who already own video-style quick release plates

Those who have a rental house full of traditional ARRI bridge plates can replace the WA-1 with the Bridge Plate Adapter BAP-1. With the BPA-1 attached, the camera can be attached to the BP-3, 5, 8 or 9.

If you have neither traditional ARRI bridge plates nor video-style quick release plates, you can equip ALEXA with the new Bridge Plate BP-12 (for 19 mm studio support rods) or BP-13 (for 15 mm studio support rods) built specifically for ALEXA. The BP-12 and BP-13 fulfill the same function as the BP-3, 5, 8 or 9. Please note that BP-12 and BP-13 are not compatible with the old style bottom plates with the thinner, spring loaded pin. They is compatible with the new bottom plates with the wider pin.

What kind of bridge plate can I use with ALEXA Studio?

Since the front foot of ALEXA Studio is larger than that of ALEXA or ALEXA Plus, a standard BP-8 (for 19 mm studio support rods) or BP-9 (for 15 mm studio support rods) can be used. For the same reason, ALEXA Studio is not compatible with the Wedge Adapter WA-1, Bridge Plate Adapter BAP-1 or any an ARRI, SONY or Panasonic video-style quick release plate.

Which ARRI accessories for hand held can I use with ALEXA?

For the most lightweight setup, attach a left and right side handgrip to the two rosettes on ALEXA’s left and right side and use the lightweight rods for matte box and follow focus. For a wider stance, use the “Extension for Handgrip” accessory (K2.47136.0) to move one or both hand grips further away from the camera. For more comfort, use ALEXA’s shoulder pad, the SP-3. If you don’t mind a little more weight, you can attach the Bridge Plate BP-12 to ALEXA, and then attach the shoulder set S-4 or S-5 to the BP-12, which gives you more options in positioning the hand grips.

We now offer the ALEXA Handgrip Set (K0.71033.0) which contains two handgrips, two extension tubes to extend the handgrips further left and right and two extensions to place the handgrips further in front of you.

Are ALEXA’s 15mm lightweight rod receptacles in the same position as on 416 and 16SR cameras? 

Yes. Diameter, distance to each other and to the optical lens axis of ALEXA’s built-in lightweight rod receptacles are exactly the same as those of the 416 and 16SR series of cameras. So all the lightweight rod accessories that have been used with the 416 and 16SR series of cameras can also be used with ALEXA.

What is the Handle Extension Bracket HEB-2 for?

As the name implies, this bracket can be used to extend the length of ALEXA’s handles. In addition, it has a built-in tape hook. When the HEB-2 is attached to the front of ALEXA’s Center Camera Handle CCH-1 with the tape hook facing upwards, this tape hook allows the assistant to attach the measurement tape to a point that is as high as possible to clear the matte box. The HEB-2 can also be attached to any other 3/8-16 UNC threaded mounting point. Please note that we also have a HEB-1, which is a slightly shorter version without the tape hook.

What is the Leveling Block LB-1 for?

When ALEXA is equipped with a bridge plate and an on-board battery, and the camera is placed on a flat surface like a table or the ground, the camera will rest on the bridge plate and the battery. Since this is not optimal for the camera/battery interface, the LB-1 can be attached to the back foot of ALEXA’s shoulder arch. Then ALEXA will rest on the bridge plate and on the LB-1.

Is it OK to cover ALEXA when it is raining?

ALEXA needs air in order for the cooling fan to work properly. Placing a plastic bag or fully enclosed rain cover over ALEXA will cut off the air supply to the cooling system. While this is OK for short periods of time, doing it for extended periods of time is not recommended. ARRI offers a special rain cover (ALEXA Rain Protector ARP-1, K2.72026.0) that has special vents built in for this reason.

Is it OK to use ALEXA in an underwater housing? 

Yes. We have run various thermal simulations and found that with both aluminum and fiber glass underwater housings the cooling effect of the water is sufficient to keep ALEXA at the proper temperature. If the water is really warm (lucky you, then), you can switch the sensor to the “tropical” mode that is available from software 3.0 on. This will run the sensor a little hotter, with no effects on image quality but with slightly higher power draw.

Sensor / Image Processing Questions
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What are the pixel dimensions of the ALEXA sensor?

The ALEV III sensor has 3392 x 2200 pixels that can be used for generating an image. There are actually more pixels on the sensor, but they are used for calibration and other purposes. ALEXA and ALEXA Plus use a 16:9 area from the sensor while ALEXA Studio and ALEXA M can be switched from 16:9 sensor mode to 4:3 sensor mode. Please note that ALEXA’s default framelines also include “ARRI 1.66” and “ARRI 2.39 Scope 1.3x”, which are not shown here for simplicity’s sake.

16:9 vs. 4:3 Sensor Modes

The 4:3 sensor area is taller than the 16:9 sensor area, but not wider. Any distribution formats that are limited by the sensor’s width (1.78:1, 1.85:1, 2.39:1 flat and 2.39:1 with 1.3x anamorphic squeeze) do not gain resolution by using 4:3 sensor mode. However, in 4:3 sensor mode those formats gain the ability for significant vertical repositioning. The one format that gains significant resolution in 4:3 sensor mode is 2.39:1 with 2x anamorphic squeeze (traditional CinemaScope).

16:9 Sensor Mode

For ProRes recording and HD-SDI outputs a 2880 x 1620 pixel area is read from the sensor. This is then debayered and downscaled in camera by a factor of 1.5, leading to a beautiful 1920 x 1080 image.
For the ARRIRAW T-link output the same 2880 x 1620 pixel area is read, but that image data is neither debayered nor downscaled in the camera. Instead, it can be debayered in post with a number of optional downscale factors, including a factor that results in a 2K image.
Both the electronic viewfinder and the HD-SDI MON OUT output can be put into surround view mode, where more is shown than the area recorded. In that case they display an area that covers 3168 x 1782 pixels from the sensor, which is 5% more on each side than the regular 2880 x 1620.

4:3 Sensor Mode

In the first versions of the ALEXA Studio and ALEXA M software, ProRes recording and REC OUT HD video output will not be supported.
The HD-SDI MON OUT output and the EVF-1 will use a 2880 x 2160 area (4:3) from the sensor, debayer and downscaled it in camera by a factor of 1.5 and display it as a pillar box image.

Pillar box means a 4:3 image with two vertical black bars (“pillars”) within the 16:9 HD image

For the ARRIRAW T-link output the same 2880 x 2160 area (4:3) area is read. That image data is neither debayered nor downscaled in camera. Instead, it can be debayered in post with a number of optional downscale factors, including a factor that results in a 2K image.
Both the electronic viewfinder and the HD-SDI MON OUT output can be put into surround view mode, where more is shown to the left and right than the area recorded. Unfortunately no surround view above and below the recorded image can be shown. In that case they display an area that covers 3168 x 2160 pixels from the sensor, which is 5% more left and right than the regular 2880 x 2160.

Optical Viewfinder

ALEXA Studio’s optical viewfinder has about the same width as the surround view in the electronic viewfinder, but it shows more on top and bottom, so when using 4:3 mode, the optical viewfinder can show a proper surround view all around.


Framelines on MON OUT are approximately 4 HD pixels wide, and framelines in EVF-1 are approximately 3 viewfinder pixels wide.

How many code values are there per stop in ALEXA’s Log C signal?

When the ALEXA Log C signal is recorded as 10 bit video, you will have approximately 80 code values in each stop above 18% grey. The original Cineon log encoding is based on the density of color negative having a gamma of 0.6. This results in 90 code values per stop. The large dynamic range of the ALEXA camera makes it necessary to use a lower gamma value. Modern color negatives, having more latitude than negatives 15 years ago, also have a gamma lower than 0.6

At which signal level is an 18% grey card in ALEXA’s Log C signal?

The nominal value for a grey card exposed according to a light meter is 38% in the Rec 709 video signal. Note that in a video signal you don’t have an equal amount of code values in each stop. Therefore, there is no easy formula telling you where, for example, 2 stops over or under are placed. The following values may be used as a guideline:

The values will vary a little bit (by 1-3%) with the exposure index. Also, bear in mind that tolerances in meters and lenses may give you slightly different results.

Which code values does ALEXA use for legal and extended range HD video on the HD-SDI outputs? 

According to SMPTE 274M 8.7, the following code values can be used for legal range HD video in 10 bit systems: 64-940 for RGB and Y and 64-960 for Cb and Cr. ALEXA complies with the code value ranges as defined in this standard.

According to SMPTE 274M 8.12, the following code values can be used for extended range (called undershoot/overshoot in SMPTE 274M 8.12) HD video in 10-bit systems: 4-1019 for RGB and YCbCr. ALEXA makes use of the full 4-1019 code values for extended range, just like the D-21.

Service QuestionsTable of Contents

How can I find an ARRI service center? 

Look at ARRI’s service contacts website.

How do I update the ALEXA software? 

You first have to register your ALEXA camera by serial number to download Software Update Packets (SUP). SUPs can then be uploaded to the camera either from an SD card, or from a computer via the ALEXA Ethernet/RJ-45 Cable KC 153-S (3.00m/9.8ft, K2.72021.0).

If you have not registered yet, go to the ALEXA downloads web page at www.arri.com/goto/alexa-dl. When the page loads there will be a selection of downloads. Please go to the section of the latest ALEXA Software Update Packet and click on ‘Please -> register to get an account.’ The ALEXA customer registration page will be opened.

Can I return to an old software version after I have upgraded my ALEXA with new software?

Even though we do not recommend it, it is possible to downgrade back to 4.0.1 from a camera that has SUP 5.0 installed. Before and after the downgrade a ‘reset to factory settings’ should be performed.

Because there is an issue with the upgrade process in SUP 2.1, we strongly recommend not to downgrade from SUP 2.1.2 to SUP 2.1. It is not possible to downgrade back to SUP 2.0 or earlier software versions and should not be attempted.

Can I use a User Setup file from a previous software version?

Unfortunately, no. User Setup files cannot be used across Software Update Packets (SUPs), i.e. a User Setup file created with SUP 4.1 is not compatible with SUP 5.0.

Where can I find pin-outs for ALEXA connectors?

The ALEXA User Manual has an appendix that shows the pin-outs for ALEXA connectors.

Further Resources & Online Tools
Table of Contents

Internet Resources

ALEXA Data Sheet

ALEXA Pocket Guide

Frequently Asked Questions

ALEXA Manual

ARRI Tech Talks

Color Processing White Paper

Internet Tools

ALEXA Frame Line Composer

ALEXA Online Simulator


 ALEXA Look Creator

ARRIRAW Converter

ARRI Meta Extract

This FAQ is also available on arridigital.com. It is current as of February 2, 2012.

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