5 Things To Consider When Shooting With The Phantom Flex4K Camera

by Adrian Pennington


Posted on Jun 11, 2020 10:46:00 AM


If you want super-sharp ultra-fast motion imaging for your next project then there really is only one camera to turn to. The Phantom Flex4K is the ultimate in slow-motion capture. Sporting a super-35mm CMOS with a full resolution of 4096 x 2304, this specialist unit produces highly detailed low noise 4K images at 938 fps. 

Originally devised for medical and scientific work by camera maker Vision Research, the Flex4K captures professional cine quality video and is a regular part of high-end commercial shoots. There’s a couple of catches though. Firstly, it’s expensive—the camera can cost upwards of $100,000, making it a rental option. Secondly, when each shot can average between 64GB and 128GB, you need to be prepared to be able to work with that much footage or your daily rental costs are going to mount.

Before you dive in, consider the following tips to efficient and expert shooting with the Phantom Flex4K.

Know how to use loop recording 

The Flex4K comes with a fixed amount of high-speed dynamic RAM. When the camera is in the pre-trigger mode (you've pressed ‘Capture’ in the user interface), the camera is continuously recording images into that memory. When it gets to the end of memory, it cycles back to the beginning and continues recording, constantly overwriting itself – until the camera is triggered. This is called ‘circular buffer recording.’
What you end up actually saving in memory is a function of how you've set up your trigger. It can be set so that only frames that occur after the trigger are saved (100% post trigger). In this mode, once the trigger is pressed any images already in memory are overwritten and you record until memory is full, then it stops. If you set the trigger to stop the recording (0% post trigger) and save all frames up to the time of the trigger, the camera will simply stop recording upon the trigger and all the frames in memory before the trigger will be saved. Or you can set the trigger anywhere in the middle, for example, having 90% of the recorded movie be what happens prior to the trigger and 10% after the trigger.

 

Choosing between ProRes and Cine Raw   

With the Flex4K you have the option of recording in Cine Raw or ProRes 422 HQ and to maintain that option you’ll need to rent either a CineMag IV or CineMag IV-PRO).

The full- size images are delivered via 9.4 Gpx throughput in the Cine Raw file format. Superfast download to CineMags can be accomplished in seconds.  For example, a 10 second clip at 1000fps would take about 40 seconds to download although more often than not you’d have trimmed the clip in-camera which would reduce download time further.

Using ProRes recording, of course, saves storage and increases total record time.

When working with ProRes, Vision Research advises the camera be set to full sensor resolution (4096 x 2304). ProRes files can be saved to the CineMag as 4K or scaled 2K resolution.  The CineMag IV will not support any other resolutions to record when set to ProRes.

In Run/Stop (RS) mode the camera will allow up to 30 fps direct to a CineMag IV, and 120 fps with a CineMag IV-PRO.  2K ProRes recording at higher frame rates is also available on the CineMag IV-PRO (in fact you can record in up to 1,775 fps in 2K).

In Loop mode, the camera will allow up to 938fps to RAM, before the file is saved to the CineMag.  Saving in ProRes HQ mode takes about three times longer to the CineMag IV than saving RAW.  CineMag IV-PRO mags are much faster, and actually the save time is equal to saving RAW.  The files in the mag are about 2.5X smaller than the un-interpolated RAW files, and take that much shorter to save from the camera or CineStation IV.  

Over five hours of 24fps ProRes HQ footage can be stored on a 2TB CineMag IV.

It’s worth noting that the camera maker has no plans to add other ProRes formats, feeling that, if higher quality is required, then Cine RAW is a better option.

5 Things To Consider When Shooting With The Phantom Flex4K Camera

How long can you record with the Flex4K?

The record time is completely dependent on the camera’s resolution, frame rate, and the size of memory that is being recorded to.  At the camera’s maximum resolution and frame rate the camera will capture 10 seconds of video to 128GB of RAM. 

A record time calculator can be found in the 'Support / Resources & Tools' section of the Phantom website https://www.phantomhighspeed.com/resourcesandsupport/calculators/framerecordtimecalculator, as well as in the ‘Phantom Tools’ iOS App, which lets you estimate the maximum frame rate and record time at any given resolution.  With the Flex4K selected, choose the appropriate CineMag and memory size in order to simulate recording directly to that CineMag.

Incidentally, there is also a frame rate and exposure calculator https://www.phantomhighspeed.com/resourcesandsupport/calculators/framerateexposurecalculator and a lens calculator https://www.phantomhighspeed.com/resourcesandsupport/calculators/lenscalculator to helps you select the correct lens for a Phantom camera based on some details about your shot.

 

Avoiding light flicker

High-speed cameras can pick up the flicker that is otherwise undetectable to the human eye creating unsightly strobe effects when played back slowed down. If you’re going to be shooting indoors at super high frame rates we recommend using at least a 2,000-watt fixture to avoid seeing the filament in the light at that wattage. In this video https://youtu.be/Ztumota98ZA, the scene is lit with a HIVE WASP 1000 watts Plasma Par with an output of 75,348 lux, which is close to a 2,500W HMI. 

The base sensitivity of the Flex4K is ISO 250T, and the exposure index can extend the image up to over 1000 (ISO equivalent) without significant loss of image quality. The Flex (2K) has a base sensitivity of ISO 1000T, but we don’t recommend pushing the exposure index on that camera in order to maintain the optimum image quality.

 

Alternatively, shoot with the VEO4K

A couple of years ago Vision Research came out with a less expensive version of the Flex4K which may tick your boxes if budget is really tight.

The Phantom VEO4K is still capable of recording 1000fps in 4K, since it has the same image sensor and codec and will record in the same CineRAW format as the Flex4K.  The workflow is the same too. Plus, its body is much more portable and it’s cheaper to rent. So, what’s not to like?

Well, the main difference is that with the VEO4K you have to offload media onto C-Fast 2.0 cards, not CineMag, a workflow that is undoubtedly slower. Rather than seconds, you could be counting minutes, and when you want to be turning media around super-fast, and probably on a time limit given you’ve only got the camera for a day or so, every second counts. 

The compromise could be worth it; but that’s one you’ll have to weigh up.


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