RedCam Central :: View topic - Demystifying "Skew" on Film Shutters and Sensors

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I felt this was important to post as many people seem to get easily confused over the issue of Skew or Rolling Shutter effects on various types of Cameras.

Here is a great explanation given by Jim Jannard (and Deanan Dasilva) of RED and how their sensors (both current and future versions) perform:

"There is a motion "feel" to a film camera due to the mechanical shutter "wipe" of the film plane. It acts just like a fast reset rolling shutter. Global shutters do not have the same "feel". Rolling shutters from the past had too slow read-reset times, which created a lot of skew. The concept is not bad, the times were just too slow. So people have an aversion to rolling shutters when they really should have an aversion to rolling shutters that are too slow "wiping" from top to bottom. We have spent two years studying this issue. Monstro will be a no excuse sensor. In fact, we think it is the ideal sensor in every way.

Just for the record... Monstro read-reset time will be less than a film camera "wipe" time. But enough to save the "feel". Less skew than a film camera... do I need to continue?

No problem... I have resigned myself to having to de-bunk the "rolling shutter myth". People tend to hang on to soundbites. We could easily do a global shutter. It just isn't the right solution. If we made a global shutter sensor, everyone would wonder why the footage looked sterile.

One of the options we have is to give the user adjustable read-reset times... just so we don't hear that we are "marketing". From zero (global) to something (what we recommend and looks right)."

[Regarding possible issues with custom frame rates and burst modes with a global shutter]

"These are separate issues. There would be no change in frame rates. It is strictly a matter of what looks best. A "fast read-reset" feels better than a global shutter. A global shutter looks better than a "slow read-reset". It is the same reason that a film camera "feels better" than a global shutter digital camera. Pretty easy stuff.

Let me give you a better example... you can choose 0-10. 0 is the same as a global shutter. 4 is the equivalent of a film camera. 40 would be the equivalent of an old rolling shutter camera. You would pick 3 or 4 for the best look. It would not be 0 and it would not be 40."

[Regarding the approximate speed of read-reset on the upcoming next generation Mysterium X sensor]

"About 5. The Mysterium X will have more DNR than Mysterium and faster read-reset. Monstro [the 5K sensor to be released after Mysterium X] will be set to "3" and have much more DNR still...

If you consider a traditional rolling shutter (with a deserved bad reputation) is, for reference, a 40... Boris and Natasha ("Crossing the Line") were about 25 (still plenty of skew). The current RED ONE (original Mysterium) is now about 8-9. Considerably better than any "rolling shutter".

Mysterium is a break-through sensor. But it is no secret that sensors still do not have the DNR of film. It is also no secret that sensors will some day surpass film in every aspect. We have a sensor program in place that will put pressure on every other sensor program AND film. The sensor is the heart of a camera. If we don't lead in this area, we do not deserve to sell cameras. The trick to all this... is to lead in sensor technology (which we plan on doing) and make the upgrades to our cameras as painless as possible. That's what will separate us from all others."

Jim