ALEXA SXT FAQ

As we like to have everything backwards compatible, using the existing adapters was our first design intention. However, since the SXR Capture Drives needed a new high-speed connector, you can end up with more electrical interfaces than is good for signal integrity. So we chose one adapter for each media family, which combines the greatest flexibility with the best signal integrity.

No, the existing XR Capture Dries will work well with the ALEXA SXT cameras. SXR Adapter and XR Adapter are included in SXT upgrades (and in new camera sets as well). SXR Capture Drives have a higher capacity and offer higher frame rates in some recording formats. The table in the ALEXA SXT Crib Sheet will give you an overview of the advantages in recording with SXR Capture Drives. 

There are two methods for clearing old data from a recording medium with ALEXA SXT cameras: Quick Format and Erase. For technical reasons, most media allows only one of those methods. Quick Format erases only the file allocation table, but leaves the actual data still on the card. Quick Format is therefore the faster method. Erase takes longer than Quick Format, but ensures that all data on the card is erased. Using Erase with SxS PRO/PRO+ cards can increase their write speed.

A sensor mode defines an aspect ratio, which defines the area on the sensor that is being captured. A recording format define what is being recorded in-camera in the file. So while a sensor mode defines a certain number of photosites on the sensor, those may be recorded straight or up or down-sampled to create the pixels of the recording format. A distribution format defines how the final product is delivered to the consumer. The contents in the recording format is often up or down-sampled, cropped, repositioned or rotated in post before it becomes the final distribution format.

An example: Choosing a 16:9 sensor mode on the camera allows the further choice of various recording formats. Choosing the 4K UHD recording format means that a 16:9 area from the sensor is read out, up-sampled in camera to a 4K UHD image and then recorded. In this case the recording format of 4K UHD is the same as the distribution format of 4K UHD. 

The 4:3 aspect ratio was originally left over from the film days, and now has been put to good use by VFX-heavy feature films. Anamorphic lenses don't actually need the full width of the 4:3 image; they squeeze the 2.39:1 image by a factor of 2, and the resulting area used on the sensor has a 1.195:1 aspect ratio, which is roughly 1.2:1, which is 6:5. When shooting with anamorphic lenses in 4:3 sensor mode, you always have to crop the extra area to the left and right of the image in post, an extra processing step that is avoided by shooting in 6:5. 

In the ALEXA XT cameras with SUP 11 we have introduced this mode, however, there it was still called '4:3 Cropped', but that is the same thing as the ALEXA SXT 6:5 sensor mode. 

To find out which lenses will work in the Open Gate sensor mode, you can use the ARRI Frame Line and Lens Illumination Tool.

Every lens is brighter in the center than in the corners: that is called the lens illumination. To get a feeling for how lenses perform in Open Gate, you first choose a sensor mode and what framelines you want to check out. Then you choose a lens model, focal length, iris and focus setting, which are all parameters that affect lens illumination. The resulting image will show how the illumination falls off towards the corners and if you get vignetting. We have most ARRI lenses in there already, but the guys are still shooting, so we will add more lenses as time goes by. You can see the result right there on the screen or save the images as a JPEG file. 

Some lenses do better and others worse. One of the lenses that does really well is our Ultra Wide Zoom UWZ 9.5 - 18; it was designed for a large image circle. Most primes under 18 mm have an issue shooting Open Gate, so the UWZ really solves the question of how to shoot wide angle with Open Gate.

ALEXA SXT cameras can record ARRIRAW just like the XT cameras could, but now with higher frame rates:

16:9 ARRIRAW up to 120 fps, 6:5 ARRIRAW up to 96 fps, 4:3 ARRIRAW up to 96 fps and Open Gate ARRIRAW up to 90 fps. 

ALEXA SXT cameras can record ProRes in HD, 2K Cine, 3.2K, 4K UHD or 4K Cine and also in the anamorphic sensor mode 6:5 in 2K and 4K. And they can do that with all high-end ProRes flavors from ProRes 422 to ProRes 4444 XQ.

ProRes 3.2K is a recording format that is quickly gaining popularity. It is being used on major TV series like Game of Thrones, on many Amazon projects and on various feature films. The reason is that it has a lower data rate than ProRes 4K UHD (in fact about 33% less data) and thus is less expensive to record on set and to process in post. It can then be used for an HD or 2K deliverable (with extra image area for re-sizing, rotating, re-framing or stabilizing) or, with only a slight up-sample, for a 4K UHD deliverable. 

With the 14 different recording formats we have in the ALEXA SXT we are offering the best image quality and most efficient workflow for the most common production, post and distribution requirements. The recording formats are optimized for different budget situations, market segments, distribution resolutions and aspect ratios, lens choices and necessary post steps including the amount of VFX work.

We are always striving to provide the best performance for each platform. As a result, there sometimes are minor differences in the actual pixel count of our recording formats. However, we are aiming to standardize as much as possible with the new cameras.

One example for this is the Open Gate format differences between ALEXA XT, ALEXA SXT and ALEXA Mini. When we first created the Open Gate format for the ALEXA XT in 2012, we had to record the full 3424 x 2202 because there are certain hardware based rules on how many pixels we can push through the camera and record. However, we found that some pixels on the edge of the frame could not be corrected by the dynamic defect pixel correction (DDPC), and so we decreed that you shall only use 3414 x 2198 of those 3424 x 2202. This 3414 x 2198 active image area is noted in metadata and the post production software should only process this area. Otherwise the very edges of the image may contain image artefacts.

While working on the ALEXA Mini and then subsequently on the ALEXA SXT, our engineers have worked out a way to make the DDPC function all the way to the edge, so now we can record and give you the full 3424 x 2202, which is, admittedly, much easier for all involved.