Rolling shutter, fluorescents/HMI, and "shutter off"

[Barry_Green]

Hey, just ran into an article talking about how the Red doesn't like shooting under fluorescents:
http://provideocoalition.com/index.php/aadams/story/red_vs_ace_hardware/

They included a sample video, which looks very much like the results I got on the Red when shooting with a magnetic-ballast HMI (although you can greatly exaggerate the effect by using a shorter shutter speed).

Anyway, it got me to thinking as to why the EX1 probably defaults to "shutter off" when in 24P mode. 1/48 = banding under fluos/hmi's, whereas 1/24 = no banding.

The reason has to do with the cycle of 60Hz lights. In order to avoid banding, you'd want your shutter speed to be a multiple of 1/120. So, 1/120 = no banding; 2/120 (i.e., 1/60) = no banding, 3/120 (i.e., 1/40) = no banding, 4/120 (i.e., 1/30) = no banding, and 5/120 (i.e., 1/24 or "shutter off") = no banding. This is going to affect any rolling-shutter camera.

So that's probably why Sony chose "shutter off" as the default. If you're shooting under fluos or magnetic HMI's, you shouldn't use 1/48 -- try 1/60 or 1/40 instead.

High-frequency electronic ballasts should overcome this issue, but you may be in a mixed-lighting situations, so better to be safe than sorry (banded). I also tried this test on the Red using the Cool Lights electronic-ballast HMI and didn't notice banding at shutter speeds up to about 1/500, so that's pretty much "safe". But magnetic ballast HMI's or low-frequency fluorescents are going to give you fits if you don't use the right shutter speed.

 

[Lenilenapi]

Thanks Barry

Lenny Levy

 

[Teeck]

OHHHHHHH!!!!!!!!!!!!!!!!!! BARRY!!!!!!!!!!!!!!!!!

I just shot a commercial with the EX1 on greenscreen, and I had this same exact thing happen. I had a bounced HMI light for fill on the subject and I was shooting 1/48th. I couldn't see this on the lcd but when I loaded the footage on my computer I saw it and was like what the hell is that? I assumed it was a shutter/light frequency issue but didn't really look into it because it wasn't really there on the actor.

This is good to know, I guess I don't mind shooting at 1/60, would be a tad smoother anyway than 1/48 and not very noticable.

These CMOS sensors are getting to be a little annoying I must say, but nothing too bad, the ex1 makes nice pictures! Thanks for the article.

 

[basilisk]

I am guessing in PAL land at 25fps with 50hz flourescents, we shouldn't have a problem.

 

[Mediacre]

So that's probably why Sony chose "shutter off" as the default. If you're shooting under fluos or magnetic HMI's, you shouldn't use 1/48 -- try 1/60 or 1/40 instead.

Nope. This is probably just a coincidence. The shutter off is set at 1/24 when in 24p because this is the right way and what actually makes sense. Shutter off means no shutter. So the exposure is the same as the frame rate you choose.
60i will be 1/60, 50i will be 1/50, 30p will be 1/30 and 24p will be well, 1/24. This is nothing abnormal and is exactly the same as the Sony high end cameras like the F900 and F23 and they are not CMOS cameras. People used to shoot with those high end cameras would not even noticed that. It's just to people who are used to use prosumer cameras that this stands out. I think the whole 24p standard shutter at 1/48 was introduced in prosumer cameras to dumb it down and make it easier for the less experienced crowed to understand and use.

The whole CMOS aversion is quite short sighted actually. CCDs have their own set of short comings. For example, last week I had to shoot a subject where a 1k light had to be in frame. With the CMOS it was no problem. If it was a CCD the shot would be unusable as there would be a very ugly line from top to bottom where the light was. CMOS also have way more dynamic range for most part. The EX1 has 10 stops of dynamic range. Which other sub 10k camera can claim that? CMOS are great and beat CCDs in many ways. Just choose the right tool for the right job.

We had to rent an EX1 last week for the above mentioned shot and I was quite impressed with the camera. Best sub 10k camera in the market in my opinion as long as you are not shooting something that as Adam Wilt puts it, will shake the camera as if it was in the jaws of a rabid dog. Rolling shutter was never a problem and we did some quite shaky handheld. It sure beats all the small cameras I have shot with. In a recent review by Wilt it stuck up pretty well against RED and the F23.

 

[Luis Caffesse]

The shutter off is set at 1/24 when in 24p because this is the right way and what actually makes sense. Shutter off means no shutter. So the exposure is the same as the frame rate you choose.

This is not 'normal' by any means.
It is standard practice to have a shutter speed that has a denominator twice your frame rate, not equal to your frame rate.

When shooting 35mm film at 24fps the normal shutter speed is not 360 (which would be the equivalent to 'shutter off') it is 180 degrees, which would be the equivalent to 1/48th when shooting 24fps.

60i will be 1/60, 50i will be 1/50

Exactly, and 60i represents 30fps, 50i represents 25fps.
So the denominator of the shutter speed is doubled from the framerate.

30fps = 1/60th shutter
25fps = 1/50th shutter

30p will be 1/30 and 24p will be well, 1/24.

I've never seen a camera default to 1/30th or 1/24th for those framerates.
But even if they did it would be a deviation from standard practice of a 180 degree shutter equivalent being the norm.

This is nothing abnormal and is exactly the same as the Sony high end cameras like the F900 and F23 and they are not CMOS cameras.

I've never worked with the F23, but I don't recall the F900 I've worked with defaulting to 'shutter off.'
But perhaps they do, and if so then perhaps it's a Sony thing overall.
Either way - I don't believe it reflects the norm.

 

[Barry_Green]

I am guessing in PAL land at 25fps with 50hz flourescents, we shouldn't have a problem.

You will have a problem if you don't have your shutter set to 1/25 or 1/50. If for some reason you change your shutter speed, you'll run into the same issue. You would need a shutter that's a multiple of 1/100.

So you're correct that by default you won't have a problem, but by usage you will if you change your shutter away from the "correct" shutter speeds (either 1/50 for 25p/50i, or "shutter off" if you want that).

 

[matthew77]

I've never seen a camera default to 1/30th or 1/24th for those framerates.
But even if they did it would be a deviation from standard practice of a 180 degree shutter equivalent being the norm.

In video, "shutter off" means "shutter off" and hence no abbreviation of the exposure.

This means 360° shutter. The HVX was the exception (Barry even says this in another thread) calling "shutter off" 180°. I am not talking defaults here but nomenclature. The default settings of the cameras are irrelevant - once you take the EX1 out of the box and switch the shutter switch from off to on, goodbye default.

If the mechanical engineers could have done it, they would have created a film camera with 360° shutter (adjustable downward from there). It's an impossibility because it takes a non-zero amount of time to pull film down through the gate. Half of the cycle was considered a comfortable amount for pulldown and registration. High speed cameras (Photosonics) and cameras with lesser mechanisms (Eyemo) have narrower shutters because they need more time for pulldown. Geneva mechanisms used in projectors have a "shutter angle" that is essentially wider than 180°, but these mechanisms are unsteady and hard on film and are not generally used in acquisition.

The 180° standard was borne out of mechanical necessity - not aesthetics. Many DP's would use a 200-270° shutter if they could. Since video has no such necessity, it can ignore this standard except for the desire to adhere to the look established over a century of film pulldown.

The HVX touts itself as a "film look" camera and adheres to that look by default. That's a great decision, but it does not change the fact that at 1/48 the shutter is defintely "on" by video standards and the nomenclature used on the HVX is atypical.

 

[Barry_Green]

The whole point of this was to point out to EX1, Red, and other rolling-shutter camera shooters, that 1/48 can screw you over when using fluorescents or magnetic HMI's.

Regardless of why 180 degrees was chosen, it was chosen and is believed by many to be crucial to the film look (I've got film cameras that range anywhere from 150 to 220 degrees, and they all look like film). So if EX1/HV20/Red shooters stick on 1/48, they may be putting their footage at risk of banding depending on what lighting they're using.

I think Sony may have defaulted to shutter off instead of 1/48 (like the Canon and Panasonic cameras do) because "shutter off" avoids the issue entirely. But that's largely irrelevant; that was just speculation based on many people asking "why does the shutter default to 1/24".

So the point is: if you're using a rolling-shutter camera, you might be better off to choose 1/40 or 1/60th. 1/48 is not necessarily a "safe" shutter speed when shooting under fluos or HMIs, unless they're high-frequency electronic ballasts. And it isn't going to impact the "film look" much at all; 1/40 equates to about 230 degrees (offhand guess), and 1/60 equates to about 144 degrees.

 

[matthew77]

I just don't know what you mean by "defaulted"

When you pull the EX1 out of the box, the shutter is switched off. That's the default. Then you switch it on, and it's at 1/48. On the HVX when you pull it out of the box it says that it's off (by pro video standards) but in fact it's on - at 1/48.

Panasonic and Canon do not follow the standard usage of the terms shutter off and on. That was my point. I agree with everything you say, Barry.

I was actually responding to Luis's specious claim that the "norm" for shutter "off" is 180° when in fact the norm in pro video for "shutter off" is 360°. Not the "defaults" (which you change within a few seconds of unboxing the camera) but the ongoing terminology used in the menus of the cameras.

Sony's way is the norm, and Panny's way is non-typical (but perhaps useful for the camera's intended purpose) in the parlance of professional video.

 

[sunporchmedia]

I think Sony may have defaulted to shutter off instead of 1/48 (like the Canon and Panasonic cameras do) because "shutter off" avoids the issue entirely. But that's largely irrelevant; that was just speculation based on many people asking "why does the shutter default to 1/24".

Barry, to clarify: Panasonic HPX500 operates just the same as the Sonys. I believe that the Varicam does also. I personally don't like the shutter-off look. I believe it is at least partly a holdover from interlaced betacam video days, before progressive video cameras. But regardless, it does behave like the Sonys and unlike the DVX100 and HVX200 cameras.

 

[Tim Naylor]

Nope. This is probably just a coincidence. The shutter off is set at 1/24 when in 24p because this is the right way and what actually makes sense. Shutter off means no shutter. So the exposure is the same as the frame rate you choose.
60i will be 1/60, 50i will be 1/50, 30p will be 1/30 and 24p will be well, 1/24. This is nothing abnormal and is exactly the same as the Sony high end cameras like the F900 and F23 and they are not CMOS cameras. People used to shoot with those high end cameras would not even noticed that. It's just to people who are used to use prosumer cameras that this stands out. I think the whole 24p standard shutter at 1/48 was introduced in prosumer cameras to dumb it down and make it easier for the less experienced crowed to understand and use.

The whole CMOS aversion is quite short sighted actually. CCDs have their own set of short comings. For example, last week I had to shoot a subject where a 1k light had to be in frame. With the CMOS it was no problem. If it was a CCD the shot would be unusable as there would be a very ugly line from top to bottom where the light was. CMOS also have way more dynamic range for most part. The EX1 has 10 stops of dynamic range. Which other sub 10k camera can claim that? CMOS are great and beat CCDs in many ways. Just choose the right tool for the right job.

We had to rent an EX1 last week for the above mentioned shot and I was quite impressed with the camera. Best sub 10k camera in the market in my opinion as long as you are not shooting something that as Adam Wilt puts it, will shake the camera as if it was in the jaws of a rabid dog. Rolling shutter was never a problem and we did some quite shaky handheld. It sure beats all the small cameras I have shot with. In a recent review by Wilt it stuck up pretty well against RED and the F23.

1/48th is the exposure time of a film camera at 24 fps. With a 180 degree shutter, exposure is half the rotation of the shutter, hence half of 1/24th, which is 1/48th. It's not a "dumming down". It's an exact replication of the cadence and motion blur of a film camera at 24fps. Shooting at 1/24th as "normal" is a misconception that people who never understood how exposure time on a film camera relates to frame rate or basic fractional math. I see this all the time since the introdution of the DVX, folks believing 1/24th is the "cinematic" setting. When in reality it's less sharp, especially with motion. It's motion blur replicates nothing you'd ever seen at a theater. In fact it would be largely considered unacceptable for large screen use.

1/24th is my shutter of last chance - when the light is too low.

Also, check your info on the the F900. It will not go to 1/24th in 24p or 1/30th in 30p. It's defaults in either frame rate are 1/48th and 1/60th. It's lowest settings are 1/32 and 1/40th. I think Sony doesn't want it's high end cameras coming back with soft images. But 1/24th exists with low end perhaps because of the low sensitivity.

CMOS aversion is just a commercial reality. I do a lot of doc and eng work for broadcast and in many situations I cannot use a CMOS chip because of sirens and flashes. Where there is news or big events going down (especially now that everyone has a camera) you'll have flashes. And flashes still look butt ugly on CMOS. Recent job I did for a network, expressly prohibited me from renting a CMOS chip. The specified very clearly that it had to be CCD and tape for that matter. Even in narrative work you're still limited for harsh light changes such as lightning or strobe.

I'll still be purchasing the EX next week for the attributes you site and more. It truly creates a magnificent image. Unfortunately, I won't be able to sell my HVX as I need to be covered for news/event/certain doc work. The best CMOS solution sadly is the most expensive: mechanical shutter ala D 20 or Dalsa. Maybe RED will one day offer the RED Hi Grade with mechanical shutter.