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

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.

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?

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

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

cool. thanks steve.