How to Shoot 200fps on the ARRI Alexa Mini
The Alexa Mini is a powerful, beautiful camera that shoots up to a whopping 200fps. But there are some strange limitations that you may not be aware of.
How to Shoot Slow Motion
The frame rate available in the Alexa Mini is also limited by the codec you choose, not to mention your resolution. ProRes 4444 XQ maxes out at 120fps in 2K or below, but simply stepping down to ProRes 4444 allows you to reach 200fps easily in 2K, 1080p, or S16 mode. Unfortunately, that does not include HD Anamorphic, which is limited to 120fps.
Once you have set your codec and frame rate with this knowledge, adjusting your frame rate is the easiest part. In the top-left corner of the settings screen, you will see one of the buttons is labeled FPS. Press it, and a list of all available frame rates appears. Simply select the one you want, and you are good to go.
How Flash Memory Works
If you have read the literature or shot on sub-optimal media, you may have noticed that there is one last factor affecting the maximum frame rate of the Alexa Mini: the size of your CFAST card. You read that right - not the speed rating, the storage capacity. Why? Because flash memory is weird. It doesn’t store data the same way spinning-disk hard drives do.
It helps to think of your CFAST card as a bunch of tiny, parallel memory cards grouped together into one super-card. When SanDisk wants to make a larger super-card, they simply group together a bunch more of these tiny cards. But this does more than just boost the storage space - a larger group also allows the camera to write to, say, six places at once instead of four. That’s potentially a 50% increase in write speed (in a perfect world, of course). Long story short? Stick to 128gb cards, and you'll never be disappointed.