F55: HFR mode - getting noise vs adjusting your exposure

starcentral

starcentral

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This topic deserves its own thread. The topic came up twice in the last day and had to do with the dreaded S&Q mode on the FS7/F5/F55 camera whereby you lose LUT monitoring capability once you switch into S&Q mode.

I've suggested between two different threads that exposure changes when shooting HFR and that you may be introducing up to 4db in gain (hence noise) when enabling S&Q mode - OR - that exposure will change between S&Q on or off and you will have to adjust your iris again to compensate for the differences in light when shooting HFR.

Ok so which is it, it can't be both? Well it can be one or the other:

Angle (when set to 180 degrees) will always expose the frame at HALF the frame rate. So 24fps = 1/48th, 60fps = 1/120th. When I test this on my camera it gets darker once I go from 24fps to 60fps. I would have to use the iris to compensate for this loss.

In speed mode however you might set the shutter to 1/48th if shooting 24fps so whether you shoot 24fps or 48fps you are still exposing with a 1/48th shutter so in that case there is no exposure compensation necessary electronically or manually via iris.

This is the strange part I noticed and I admit I have to go back and test it some more when I get a chance - what I noticed looking at the metadata in Catalyst Browse was 4db gain applied to my S&Q shots which I was surprised to see because I remember having to adjust my iris between having S&Q mode on or off.

Possibly yet another separation between custom mode vs CineEI when it comes to HFR.


What has everyone else's experience been, if any?
 
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My exposure definitely changes. No idea what the deal with some people having gain compensation of some kind switched on. Don't recall that option.

In therms of my workflow - If I know I'm going to use HFR as well as synch shooting on a shot, I expose the sync stuff using the in-built ND filter and go back a notch on the wheel when doing the HFR stuff so aperture/shutter/gain are all the same and the WFM is vaguely in the same place. Has worked well for me so far.
 
Under your shutter menu do you have angle or speed selected?

And if you could, check out the metadata in Catalyst Browse for those clips… somewhere half way down is a heading that reads: "camera master gain adjustment". That is where I saw +4db gain on mine.
 
Varies as I've been seeing what effect different settings have on the shutter bug, but regardless I'm always shooting a 180deg shutter, even if I change it manually. Usually I'd just leave it as angle and 180deg
 
I have had some noisy HFR, but I thought that was simply I hit the SQ button and the image gets dark (as expected with 180 angle) then I open up a bit of iris, often wide open, but that was not enough.. my though on noisy SQ

S
 
As I see it the sensor has to take a few short cuts in order to output 180fps hence the added noise, aliasing an moire. I find it best to expose until the high light warning comes on for HFR shots.
 
I use shutter angle (180) and it gets predictably darker once I engage S&Q due to 180 shutter. I'll have to check CatBrowse to see about gain.

S&Q over 60 is one mode where underexposure creates awful noise. In those situations I end up switching to Custom and going up ISO to feed the sensor more. Going up ISO has yielded better results than a lower ISO but starving the sensor for me.
 
For me, and I switch frame rates a lot, there is absolutely no change in exposure, just an increase in noise in HFR, so I tend to 'lift' exposure in those circumstances.
 
Very interesting. And how is your shutter set Liam? Would love to track down this mysterious gain you're getting applied to the image to maintain the same exposure.
 
Most of the time, it's 180 degree. Sometimes, I sharpen the image with a shorter shutter, but the important point is, the shutter always behaves in a reciprocal manner.
 
Liam Hall said:
For me, and I switch frame rates a lot, there is absolutely no change in exposure, just an increase in noise in HFR, so I tend to 'lift' exposure in those circumstances.
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How can there be no change in exposure if shutter speed changes? Of course exposure changes, all you need to do is look at the waveform and you'll see. The difference is just short of 3 stops when you go from 24fps to 180fps (assuming the shutter angle stays at 180 degree angle), as expected and the same as in any other camera, film camera included. You contradict yourself by saying that "I tend to 'lift' exposure in those circumstances" - it is simply because it is as if you shot at higher EI rating effectively, your neg is thinner which results in increased noise.
 
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I've only used it once, at 180 fps 2k center scan mode. The shot was beautiful. But as I recall, my shutter had been on 1/60 and the camera adjusted it to 1/180 sec. I left it at that and adjusted my exposure with the iris.

So my question is, what would be the reason for using a 180 degree shutter at this frame rate? Seems like a waste of an f-stop.
 
Tom Roper said:
I've only used it once, at 180 fps 2k center scan mode. The shot was beautiful. But as I recall, my shutter had been on 1/60 and the camera adjusted it to 1/180 sec. I left it at that and adjusted my exposure with the iris.

So my question is, what would be the reason for using a 180 degree shutter at this frame rate? Seems like a waste of an f-stop.
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Yes, you could say that it is a waste of an f-stop but it is done to keep specific level of motion blur, usually the pleasing rendering of motion is at 180 degree shutter. But you are right, sometimes it is not necessary. In film days ARRI 435 camera had a feature where you could change the frame rate and keep the same exposure, camera was compensating by increasing (opening) the shutter angle, all done smoothly in sync during the shot. Similar thing was done prior to this invention in "Raging Bull", the ring boxing scenes have frame rate ramping, the loss of exposure is compensated by opening the iris. The side effect of it was the change of depth of field, to mask it most of the ramping shots are shot against background where it is hard to see the change of depth of field (often pitch black background).
 
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At 180 fps/360 degree shutter, a frame is 1/180 sec exposure which is still fast enough to freeze some action and more smoothing blur than 180 degree shutter, so my open shutter would tend toward more blur.

While 180 degree is customary for motion picture rates like 24 fps, it's less relevant at higher frame rates. What comes into play with me is the hand holding rule for 35mm photography, that the shutter should be at least as fast as the reciprocal of the focal length, ie with 180mm lens shutter at least 1/180 sec. At high frame rates, there would not in my opinion be a big difference in blur characteristics between 180 degree vs 360 degree at the frame rate of 180 fps or 240 fps.
 
Tom Roper said:
At 180 fps/360 degree shutter, a frame is 1/180 sec exposure which is still fast enough to freeze some action and more smoothing blur than 180 degree shutter, so my open shutter would tend toward more blur.

While 180 degree is customary for motion picture rates like 24 fps, it's less relevant at higher frame rates. What comes into play with me is the hand holding rule for 35mm photography, that the shutter should be at least as fast as the reciprocal of the focal length, ie with 180mm lens shutter at least 1/180 sec. At high frame rates, there would not in my opinion be a big difference in blur characteristics between 180 degree vs 360 degree at the frame rate of 180 fps or 240 fps.
Click to expand...

Same exact relevance of motion blur as in 24fps, it is just as noticeable.
 
Are you noticing the gain up on CineEI mode Dennis? Or just in Custom?

I don't do a huge amount of HFR work, but I can't say I've ever noticed exposure issues when I've shot it (adjusting my meter accordingly). I'm only shooting in CineEI mode though.
 
broughtonfilm said:
Same exact relevance of motion blur as in 24fps, it is just as noticeable.
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An object moving across the frame traverses half the distance with each doubling of frame rate. If the object is not moving there is no blur. Blur is therefore the displacement of the object within the static frame. There is less displacement and therefore, less blur as frame rate increases. Your point would be; although you have not articulated it this way, is that temporal motion (motion-blur) remains constant. True but the acuity required to discern it is more. It is that characteristic demand to discern with acuity that makes instant replay both invaluable yet flawed. You see clearer with less blur, but because temporally as the frame rate is increased, a dropped pass looks like a catch because the ball spends more time in the receiver's hands.

180 shutter adds very little blur reduction to a frame rate that's already fast enough to minimize blur.
 
If the camera is set to 180 degree then surely your picture has to go darker as your shutter speed will go up.. when you up the frame rate.. the camera is automatically adjusting to a 180 shutter angle.. and your going to need more light to compensate for it.. nothing new there I guess..
No hard and fast rules but over 60 fps do you really need all that shutter to avoid motion blur.. which is why we have it for 24/25/30.. only if your shooting a water fall or very fine detail..
Also check with your dir that they are not going to want to ramp it... much beloved of commercials and 99.9% of all music clips.. ! very high shutter wont good look back at 24 fps.. very staccato .. (well you could say you did that on purpose and put your rate up) ..

Wrote this before the above seeing the above posts ..
 
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Tom Roper said:
An object moving across the frame traverses half the distance with each doubling of frame rate. If the object is not moving there is no blur. Blur is therefore the displacement of the object within the static frame. There is less displacement and therefore, less blur as frame rate increases. Your point would be; although you have not articulated it this way, is that temporal motion (motion-blur) remains constant. True but the acuity required to discern it is more. It is that characteristic demand to discern with acuity that makes instant replay both invaluable yet flawed. You see clearer with less blur, but because temporally as the frame rate is increased, a dropped pass looks like a catch because the ball spends more time in the receiver's hands.

180 shutter adds very little blur reduction to a frame rate that's already fast enough to minimize blur.
Click to expand...

No, I did not say the motion blur remains constant, this can happen only when you double / halve frame rate - for example, you shoot at 24fps with 180 degree shutter and then you go to 48fps but the shutter angle is 360 degree (the resulting shutter speed is the same, so is motion blur), but if if you go past that, the shutter speed is reduced because the shutter angle can't be greater than 360 degree, it can't compensate more.
 
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