slow shutter mode

T

themagickite

Well-known member
iv'e been trying to get my head round it but i just can't think a way that you could have a shutter speed slower than your framerate, could someone please explain the slow shutter effect?

also what kind of look does it have?
 
You can easily lower shutter speed all the way down to 1/4, it has little to do with framerate except that the standard is 1/48 for 24p. The effect is more light but more motion blur the lower you go.
 
hmm, but if it's taking 24 (or 25) differenct frames per second, then....?
you wouldn't be able to do this on a real film movie camera would you?

for 1/4 sec, does it take one 1/4sec image and spread it across 6 frames?

that would make sense, but that would make this an effect you can only pull off with video right?
 
why is it that 1/48 is the standard, does it make the image look better? cause when i use it i see no difference. What does it exactly do??
 
So far as I can tell a shutter speed of 1/6 second in 24pa mode records the same frame 4 times. It is very blurry and jerky. It also increases the exposure, so it would be useful in a very dark environment where there's little motion. Of course, you might also want that look for aesthetic purposes.

I think you could get something like the effect in a film camera by shooting 6 frames per second and then duplicating each frame 4 times in post.

1/48 is the standard simply because that's the way film cameras operate. A film camera needs to stop exposing the film while it moves from one frame to the next. I imagine that originally it was easiest to build cameras that had half the time to move film and half to expose it. Current cameras have more options, but I'll let someone who has actually used one expound on that.
 
well 48 is half of 24, and that means the shutter is set to 180 degrees for each frame of video only half of the time it takes to record that frame the ccd is exposed to light

on 25p 50 would look the same

most cine cams have a standard 180 degree shutter, which is why a lot of people trying to get "the film look" use 180 degree shutter (48th of a sec, for 24p) but a lot of cine cams allow you to vary that angle less than 180 for sharper high speed motion, more than 180 for lower lighting conditions (or blurred motion effects) i just can't see how you could get a shutter speed lower than the framerate

if the framerate is 24p, then for each second 24 separate images are recorded. at 48th/sec each frame is exposed for half the duration of recording and playback

the dvx and other cams allow shutter speeds below the recording framerate, which mean that on 24p each frame could be exposed for 1/4 of a second
to me this doesn't add up. each frame in a 24p camera should hold 1/24th sec of time or less recorded at normal motion speed, and played back at normal motion speed, how can you record more time onto a frame than it is exposed for? doesn't make any sense! arg!

i'm sure it's simple enough, and i can imagine different ways in which it could really expose 1/4 sec at 24p at normal motion, but i want to know how the cameras do it
 
For less than 1/24 shutter, it has to either expose at a full 1/24th second and cache a number of frames, blending them together... or it has something to do with how it discharges the CCD's. Either way, I do believe that each frame is different, it's not just repeating frames.
 
It does repeat frames, at least on the DVX and every other cam I've seen. If you're getting a shutter time that lasts longer than an individual frame does, then the cam enters what is called "frame accumulation mode"; it buffers up the frames until it's finished its exposure. The tape (or other recording mechanism) keeps writing out the last frame it's been handed until the new frames are ready. So at 1/30 shutter, in 30fps, you'd get 30 distinct frames. In 1/15 shutter, you'd get 15 distinct frames, each one duplicated once.
 
I stand corrected.

Regardless, repeated frames or not, it's still good if you are speeding it up in post, since numerous frames will be dropped or blended.
 
It doesn't "help". It's just a look. It happens to be the same look that you'd get with a film camera (although of course there are other things that make the result look different). Some people like that, others don't.
 
Well if you used 1/24 it would have alot of motion blur, but usually you multiply the frame rate by 2 and that's what you used to avoid strobing. The 1/48 also is what film cameras use so it helps achieve the film look.
 
1/48 shutter doesn't help anything. It is simply the equivilant to what most films are shot at. 1/48th shutter is the same as film at 24fps with 180 degree shutter.
 
so using the 1/3 shutter speed on the pal dvx would give you 3 frames per second at normal motion speed when played at 25fps (and each single frame of image would last 8.333 frames on the timeline/timecode).

so in progressive mode, would 1 frame of dvx footage shot at this rate be exactly the same as 1/3 shutter speed image on a still camera? (bar any resolution, dof or lattitude issues)
 
Yes, pretty much. Each frame will be held for 1/3 of a second, so each frame will get recorded 8 times, 8 copies of the same frame, with 1/3-second exposure. Played back at real-time you'd get a very posterized-time effect. If you speed the footage up by a factor of 8, then you'd get a frame-accurate simulation of if you'd shot film at 3fps.
 
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