Over-Crank 60fps : Light Loss? at DVinfo.net

Michael B. McGee · May 12th, 2009, 02:48 PM

ok, help me do the math. if i'm shooting 24P at 1/48th or 180 degree shutter and i decide to over-crank to 60fps with "equivalent" shutter speed of 1/120th, am i going to loose 3 stops a light? 1.5 for frame rate and 1.5 for the shutter speed difference. right? so, if i'm lighting an interior and i normally shoot at lets say f/2.0, i'd have to light for a f/5.6 in case i decided to over-crank to 60fps. it that right? please no comments on pumping up gain or filter light loss to consider.

thanks,
Mike

Bob Grant · May 12th, 2009, 04:47 PM

Yes, you will loose light.
If you keep the shutter angle constant then the time the shutter is open for is function of the fps. Double the fps and the time the shutter is open halves hence half the light.

Don Greening · May 12th, 2009, 05:11 PM

Why not confirm your theories by doing a little test with the camera's spot meter activated. I just did a bit of a test myself and set the EX1 @ 720P 24 and 1/48th shutter. I cranked the iris until the spot meter read an even 70%. Then I changed shutter speed to 1/120th sec. and enabled over cranking to 60 fps. The spot meter went down to 42%. I never touched the iris or moved the camera.

- Don

Michael B. McGee · May 16th, 2009, 12:00 PM

Quote:

Originally Posted by Don Greening

Why not confirm your theories by doing a little test with the camera's spot meter activated. I just did a bit of a test myself and set the EX1 @ 720P 24 and 1/48th shutter. I cranked the iris until the spot meter read an even 70%. Then I changed shutter speed to 1/120th sec. and enabled over cranking to 60 fps. The spot meter went down to 42%. I never touched the iris or moved the camera.

- Don

oh boy, does 70% -(minus) 42% = 3 stops?

Steve Phillipps · May 16th, 2009, 02:47 PM

No, you'll only lost just over a stop as the frame rate is irrelevant, it's just the shutter speed that matters. Each frame is exposed for whatever the shutter speed is set to, down to a minimum of the frame rate (ie you can't have 1/25th second at 50fps!)
So looking at it another way, if you set 1/48th shutter it'd be the same exposure for each frame if you shot at 24P or 60P.
Steve

Michael B. McGee · May 16th, 2009, 03:49 PM

Quote:

Originally Posted by Steve Phillipps

No, you'll only lost just over a stop as the frame rate is irrelevant, it's just the shutter speed that matters. Each frame is exposed for whatever the shutter speed is set to, down to a minimum of the frame rate (ie you can't have 1/25th second at 50fps!)
So looking at it another way, if you set 1/48th shutter it'd be the same exposure for each frame if you shot at 24P or 60P.
Steve

your 1/48th statement is false. if you set your camera to shoot at 60fps then 1/60th (360 degree) would be your slowest shutter speed. you're right about frame rate though. i just figured it out. thanks to all who answered.

-Mike

Steve Phillipps · May 16th, 2009, 05:00 PM

Quote:

Originally Posted by Michael B. McGee

your 1/48th statement is false. if you set your camera to shoot at 60fps then 1/60th (360 degree) would be your slowest shutter speed. you're right about frame rate though. i just figured it out. thanks to all who answered.

-Mike

Yeah, what I meant was keeping your shutter speed constant, slipped my mind that 1/48th was slower than 60fps - I'd said earlier that you're limited by your frame rate as to the slowest speed you can use!
Steve

Michael B. McGee · May 17th, 2009, 09:32 AM

cool. thanks steve.

May 12th, 2009, 02:48 PM	#1
Michael B. McGee Major Player Join Date: Nov 2008 Location: Santa Monica, CA Posts: 318	Over-Crank 60fps : Light Loss? ok, help me do the math. if i'm shooting 24P at 1/48th or 180 degree shutter and i decide to over-crank to 60fps with "equivalent" shutter speed of 1/120th, am i going to loose 3 stops a light? 1.5 for frame rate and 1.5 for the shutter speed difference. right? so, if i'm lighting an interior and i normally shoot at lets say f/2.0, i'd have to light for a f/5.6 in case i decided to over-crank to 60fps. it that right? please no comments on pumping up gain or filter light loss to consider. thanks, Mike

May 12th, 2009, 04:47 PM	#2
Bob Grant Trustee Join Date: Nov 2005 Location: Sydney Australia Posts: 1,570	Yes, you will loose light. If you keep the shutter angle constant then the time the shutter is open for is function of the fps. Double the fps and the time the shutter is open halves hence half the light.

May 12th, 2009, 05:11 PM	#3
Don Greening Regular Crew Join Date: Dec 2007 Location: Port Coquitlam BC Canada Posts: 179	Why not confirm your theories by doing a little test with the camera's spot meter activated. I just did a bit of a test myself and set the EX1 @ 720P 24 and 1/48th shutter. I cranked the iris until the spot meter read an even 70%. Then I changed shutter speed to 1/120th sec. and enabled over cranking to 60 fps. The spot meter went down to 42%. I never touched the iris or moved the camera. - Don

May 16th, 2009, 02:47 PM	#5
Steve Phillipps Inner Circle Join Date: Apr 2006 Location: Wales Posts: 2,130	No, you'll only lost just over a stop as the frame rate is irrelevant, it's just the shutter speed that matters. Each frame is exposed for whatever the shutter speed is set to, down to a minimum of the frame rate (ie you can't have 1/25th second at 50fps!) So looking at it another way, if you set 1/48th shutter it'd be the same exposure for each frame if you shot at 24P or 60P. Steve

May 17th, 2009, 09:32 AM	#8
Michael B. McGee Major Player Join Date: Nov 2008 Location: Santa Monica, CA Posts: 318	cool. thanks steve.