Why is 50p (720p) not 1 stop darker than 25p (1080p)?

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Drcoffee

Well-known member
With the GH1, why is 50p (720p) not 1 stop darker than 25p (1080p)? when using the same shutter?

Cheers
Jon
 
I too heard that it should be like this when I initially got the GH1 and when I tested it out initially it did show that 1080P in same lighting is brighter than 720P.

But later when I tried to do the same thing after few months I did not get the same results. And I'm sure that I did see during that time that 1080P is brighter under same lighting.
 
exposure is down to the iris and shutter speed - for both these frame rates the shutter speed will be 1/30 hence the frame rate has no effect on exposure.

you might be thinking at 25fps it would be 1/25second and at 50fps it would be 1/50second

If this were the case then you would see it slightly darker at 720p. I think panny chose 1/30 as a good compromise of the two.

hope this answers ya question
 
I don't even understand the logic of why anyone would think that framerate should affect exposure unless the film/sensors are unable to be exposed properly in the alloted time.

Think about a photographer. He sets an F8 & 1/60 exposure. Takes a picture, it's fine. Takes another and it's fine. Takes three in rapid succession and they should be darker?
 
I think on a film camera if you shoot 25fps or 50fps at the same shutter angle (180degrees)

25fps frames would be exposed for half of its life (180 degrees) ie. 1/50 of a second.
50fps frames would be exposed for half of its life (180 degrees) ie. 1/100 of a second. (1 stop darker, half as much exposure...?)

is this right?
 
I saw it happen it with my own eyes when the camera came out after someone mentioned about the same thing, but later when I tried it didn't seem the same as before. I wonder why and I never bothered about checking it again...
 
drcoffee2 said:
I think on a film camera if you shoot 25fps or 50fps at the same shutter angle (180degrees)

25fps frames would be exposed for half of its life (180 degrees) ie. 1/50 of a second.
50fps frames would be exposed for half of its life (180 degrees) ie. 1/100 of a second. (1 stop darker, half as much exposure...?)

is this right?
Click to expand...

Yes... shutter ANGLE is a variable. Shutter SPEED is not.
 
I take it you can't video at frame speeds more than 50fps at 1/50 shutter speed then, on a digital camera, as the shutter is constantly open already...?
 
PerroneFord said:
Yes... shutter ANGLE is a variable. Shutter SPEED is not.
Click to expand...

Uh?... Shutter speed is the implementation of 'shutter angle' on the SLR. Frame rate sets the max, shutter speed sets the duration in that time. What can't be done is setting shutter speeds for longer than the frame rate, for whatever reason some may want to do that.

The usual recommendation of shooting at 1/2 the frame rate would yield shutter speeds of 1/50 for 24 (closest to 1/48) and 1/50 for 25 (exact), and 1/60 for 30, and 1/120 and 1/100 for 60 and 50 respectively.

What some people may be doing is shooting at 1/50 for the lower frame rate, and going to almost '360 shutter' angle, when shooting at either 50 fps or 60 fps respectively, and so would not see a 1 stop drop in levels, because they are shooting almost at the same 'shutter speed' as before.

If they would shoot the 60p (50p) at the 'recommended' shutter angle of 180, they would be adjusting their shutter speed to 1/120(1/100) or whatever is close...
 
drcoffee2 said:
I think on a film camera if you shoot 25fps or 50fps at the same shutter angle (180degrees)

25fps frames would be exposed for half of its life (180 degrees) ie. 1/50 of a second.
50fps frames would be exposed for half of its life (180 degrees) ie. 1/100 of a second. (1 stop darker, half as much exposure...?)

is this right?
Click to expand...
Default shutter speed for 50i/50p is 1/50 s. Similarly, default shutter speed for 60i/60p is 1/60 s. Hence no improvement if you shoot 25p with 1/50 s.
 
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