Another CMOS question

[zak forrest]

Could someone give me a few scenarios where one would use the Red and a flash at 1/30,000th of a second?

 

[Mike Smith]

Zak, you wouldn't WANT to use a short duration flash with Red, and on a controlled set, you wouldn't have that issue. Some scenarios where you might be exposed to it... filming a concert, fashion catwalk, celebs at a red carpet event (Oscars)... in other words anywhere you'd be exposed to uncontrolled flash photography. But the worst that would happen is you'd have frames that were partially lit by the flash because the flash would be much shorter duration than the rolling shutter can go from top to bottom of the frame. In reality, I don't know if it would be that noticeable while watching the shot. If you were using this footage as "real" input to a narrative film, you may have to do something in post to fix it. In the past, I have seen films - long before Red came out - where they literally whited out an entire frame to represent the flash photography.

As I said, Red offers me far too much to worry about this issue. The non-flash issues such as warping from camera motion, I'm not concerned about at all as I don't intend on waving the camera about that wildly.

 

[zak forrest]

But do people even use 1/30,000th of a second when shooting a catwalk or red carpet event? I don't know anything about it, but it seems really excessive to me.

This just seems ridiculous and pointless to even bring up, like telling someone to avoid shooting helicopters or the wheels of a car because it will look like it's running backwards instead of forwards and that they would have to fix it in post. The rolling shutter on the Red is practically like any other motion picture film camera, and if you shot 35mm at the red carpet, well, whatever..

Also I think the motion is completely fine if you did decide to wave the camera around wildly.

I remember when some FX guys were on these boards and concerned with rolling shutter because it made their job a bit more difficult, I can understand that. But any other talk about rolling shutter on this camera just feels ridiculous to me. Sorry to fan the rolling fire, didn't mean to go off like that, I just wanted to know more about 1/30,000th of a second flash, and when people would actually use a speed that high...

 

[Mike Smith]

Yeah, I'm not sure why you're "going off" like that either. You asked the question and I answered it in as straightforward and unbiased way as I could. By all means feel free to wave your camera about while shooting. I didn't say you shouldn't - just that I don't intend to.

An intelligent flash gun does not vary its brightness for exposure but it varies the duration. With a tight shot, the feedback can make this a very short duration indeed. Remember, the shutter speed on your stills camera during flash photography has nothing to do with flash duration so you don't set flash duration as such.

 

[Erik Widding]

In any case, an SLR with a focal plane shutter has always had the same issue yet no-one seems to consider it a problem.

The only issue I see as insolvable with a RS sensor is flash photography in the scene which can be of extremely short duration; perhaps as short as a 30,000th of a second. No RS sensor can protect against that, at least not to my knowledge.

Focal plane shutter is a really good example of the issue, and the solution. Flash simply needs to be fired when the shutter is completely open. This is one of the reasons that flash sync on an SLR is limited to lower shutter speeds.

Could someone give me a few scenarios where one would use the Red and a flash at 1/30,000th of a second?

If you need to freeze motion, as in bullets, golf balls, water, etc. Probably not going to get enough speed out of RED ONE just yet for this, think Phantom rental until EPIC comes out... We are using 1/50,000 sec strobe to track golf balls moving 200mph, 18" away from the camera, for a project we are doing for a club manufacturer. Admittedly we are using a global shutter sensor, but you don't have to.

As long as the energy hitting your sensor from your strobe excedes that from the ambient light source by a 100x (or more, for more dynamic range and more freezing power), you can use the light source as the shutter. Unfortunately this can mean needing a strobe with a peak brightness 100,000 times ambient. Stated differently, ambient light hits the sensor for the entire exposure time, and the strobe for maybe 1% of that time, you need your light to be 100/0.01 times ambient.

So, think soundstage, not bright sunlight, as the opportunity to employ such a tactic. Though, in the first implementation of the golf system we did just this, double firing the strobe to get two frozen images in a single exposure:

For those that need to control lighting or effects, it would seem this would all become moot if the camera had a sync output that told you when the entire sensor was collecting light. Definitely can't do this at all shutter angles, and shutter speeds, but I would be willing to bet, if the sensor can go 60fps at 4K, you could do it with a shutter angle of 90+ degrees at 30fps.

The basic idea... sync your events to your camera, not your camera to the events.

 

[WILLIAM SPENCE]

Thanks for the insight Jim. Truly I am just curious as to how to improve CMOS, not to stir up debate on why or why it isn't an issue. For the way that I shoot, skew is not an issue, but flashes might be for the events that I cover. I think that everyone can agree that early CMOS designs had great image quality but rolling shutter issues. I think the best example is the HV20(and no, I am not comparing RED to that little Canon camera) From what you have said, making the read-reset times faster is all that is necessary to make this all but disappear - and without the cost, image repercussions and design complications that come with a CMOS global shutter. I think this is FANTASTIC news and is a solution that will make everyone happy. Good to know, and even better to know that this is something else to look forward to with Scarlet/RED/EPIC.