How does XF400 handle shutter speed and gain in aperture priority?

Bryan Worsley · November 28th, 2019, 03:23 PM

I don't put 60p on a 30p timeline as a rule, but surely you will only get judder if you let the program convert to 30p by frame deletion. On the odd occasion I have done it (in DaVinci Resolve) for (half-speed) slo-mo, I simply changed the declared frame-rate of the clip (in Clip Attributes) to match that of the project.

Ron Evans · November 28th, 2019, 03:40 PM

I do not like slow frame rates so do not use 30P. However if you put 60P on a 30P timeline with 1/120 shutter you will get judder. It is the fact that each frame is too sharp that causes the judder at slow frame rates. The 180 rule was set to cause motion blur that fools the eye into thinking there is motion. If the image is sharp then the eyes will not be fooled. Hence the rule. If the sample rate is above about 48fps then the eyes perceive as motion rather than a series of still images so there is no need to closely follow the rule as there will not be judder anyway as the frame rate by itself is fast enough for our eyes to perceive as motion. If you want to take stills off the video then of course you need to set shutter to "freeze" the image. At 1/60 there is still the motion blur like 30P of course however there are twice as many frames so the motion will look smoother especially if panning. Slow motion is different to 30P video and yes for a full video intended to run at normal speed frames will be dropped but will be exactly as if the original was shot at 30p with 1/60 shutter. Yes panning shots will look smoother on the original 60P and may judder at 30P because frames are missing. Exactly the problem of shooting slow frame rates whatever the shutter speed.

Bryan Worsley · November 28th, 2019, 06:13 PM

I don't see how 60p shot with 1/60 shutter and imported onto a 30p timeline (so alternate frames will be dropped, unless blended) "will be exactly as if the original was shot at 30p with 1/60 shutter" - if that's what you are saying? I agree its probably the closest approximation you'll get to native 30p with 1/60 shutter in that case, but the motion blur characteristics will be different.

Anyhow, like I said, I don't shoot 60p for 30p projects. My only point was that the older XA/HF-G models don't offer 1/120 sec (or 1/125) as a selectable shutter speed for 60p whereas the 4K models, XF400/405/GX10 included, do offer 1/120.

November 28th, 2019, 03:23 PM	#16
Bryan Worsley Major Player Join Date: Oct 2005 Location: Canada Posts: 439	Re: How does XF400 handle shutter speed and gain in aperture priority? I don't put 60p on a 30p timeline as a rule, but surely you will only get judder if you let the program convert to 30p by frame deletion. On the odd occasion I have done it (in DaVinci Resolve) for (half-speed) slo-mo, I simply changed the declared frame-rate of the clip (in Clip Attributes) to match that of the project.

November 28th, 2019, 03:40 PM	#17
Ron Evans Inner Circle Join Date: Mar 2003 Location: Ottawa, Ontario, Canada Posts: 4,222	Re: How does XF400 handle shutter speed and gain in aperture priority? I do not like slow frame rates so do not use 30P. However if you put 60P on a 30P timeline with 1/120 shutter you will get judder. It is the fact that each frame is too sharp that causes the judder at slow frame rates. The 180 rule was set to cause motion blur that fools the eye into thinking there is motion. If the image is sharp then the eyes will not be fooled. Hence the rule. If the sample rate is above about 48fps then the eyes perceive as motion rather than a series of still images so there is no need to closely follow the rule as there will not be judder anyway as the frame rate by itself is fast enough for our eyes to perceive as motion. If you want to take stills off the video then of course you need to set shutter to "freeze" the image. At 1/60 there is still the motion blur like 30P of course however there are twice as many frames so the motion will look smoother especially if panning. Slow motion is different to 30P video and yes for a full video intended to run at normal speed frames will be dropped but will be exactly as if the original was shot at 30p with 1/60 shutter. Yes panning shots will look smoother on the original 60P and may judder at 30P because frames are missing. Exactly the problem of shooting slow frame rates whatever the shutter speed.

November 28th, 2019, 06:13 PM	#18
Bryan Worsley Major Player Join Date: Oct 2005 Location: Canada Posts: 439	Re: How does XF400 handle shutter speed and gain in aperture priority? I don't see how 60p shot with 1/60 shutter and imported onto a 30p timeline (so alternate frames will be dropped, unless blended) "will be exactly as if the original was shot at 30p with 1/60 shutter" - if that's what you are saying? I agree its probably the closest approximation you'll get to native 30p with 1/60 shutter in that case, but the motion blur characteristics will be different. Anyhow, like I said, I don't shoot 60p for 30p projects. My only point was that the older XA/HF-G models don't offer 1/120 sec (or 1/125) as a selectable shutter speed for 60p whereas the 4K models, XF400/405/GX10 included, do offer 1/120. Last edited by Bryan Worsley; November 29th, 2019 at 12:45 AM.