how do camcorders sense / meter light?

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cheeky_chappie

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Tim
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this might be a STUPID question but i'm going to ask anyway :bonk:

did my first video shoot with my new continuous lighting set yesterday, out of the 3 x 500w heads i decided to try using 2 of them, location was a small lounge. for most of the shoot i had 1 x head either side of me and i was standing just behind or aligned with them. sometimes i ventured into the lit scene.

on reviewing the content what i am surprised at is the scenes where i was behind or aligned with the heads aren't as well lit as the scenes where i ventured into the lit scene i.e. in front of the heads. i would have thought both scenes would have been well lit regardless of where i was standing i.e. the camera is looking onto a well lit scene even though it's located just behind the lighting heads.

so my question is where does a camcorder meter from i.e. what's it 'looking' at for metering light? do i always have to be in front of the lighting heads to ensure a well lit scene?
 
very good question actually! I'd love to know too lol.....
 
On a similar note, I've always wondered how film cameras manage aperture when the 'shutter speed' - the 24fps film - never changes? I guess video just changes its light sensetivity but with film, how? Off topic I know but....
 
specialman said:
On a similar note, I've always wondered how film cameras manage aperture when the 'shutter speed' - the 24fps film - never changes? I guess video just changes its light sensetivity but with film, how? Off topic I know but....
Click to expand...

I think that the 24fps is more akin to the frame wind speed on a film slr. The frame moves on, stops, a shutter opens and closes same as a stills camera, then the frame winds on. 24 times a second. Okay - so it means that shutter speeds of slower than 1/25" are out, but that's all. Aperture is same as stills too. And if they want lower-light capabilities they use "faster" film. Same as us luddites with 35mm slr's do.
 
TheBigYin said:
I think that the 24fps is more akin to the frame wind speed on a film slr. The frame moves on, stops, a shutter opens and closes same as a stills camera, then the frame winds on. 24 times a second. Okay - so it means that shutter speeds of slower than 1/25" are out, but that's all. Aperture is same as stills too. And if they want lower-light capabilities they use "faster" film. Same as us luddites with 35mm slr's do.
Click to expand...

That clears that up. Phew, I can get back to normal life now... Cheers Big Yin :D
 
I knew that the shutter was separate from the film transport - don't some cameras use rotating mirror shutters?
 
only Cine camera I've used was a old super-8 that a mate borrowed from college to shoot a mini-documentary project about me and him spending a summer climbing in the alps. Was a wierd thing, strange combination of high precision and extremely clunky. Vaguely remember that it had a through the lens viewfinder and a zoom lens that kept freezing up half way up Mont Blanc/Matterhorn etc :)
 
Steve Smith said:
On a film movie camera, the shutter is usually a 50% opening in a disc which rotates at at 24 rotations per second for 24 fps film speed. This translates to a shutter speed of 1/48s.

http://upload.wikimedia.org/wikipedia/commons/a/ad/Moviecam_schematic_animation.gif

As can be seen in the above animation, the film is advanced whilst the shutter is closed.


Steve.
Click to expand...
Great animation that. Just when you think you understand a topic, two technologies collide and suddenly you're expected to know how hollywood works :)
 
I don't have a technical answer but from using a camcorder it seems to be an averaged exposure for the entire frame.

Shooting indoor family videos in the daytime I have to avoid getting any of the window in the shot as the rest of the indoor scene will be under exposed as soon as bright daylight becomes a small part of the shot.

So I'd suggest you look at the relative brightness of areas in the shot and see if a small bright area is pulling down the rest of the frame.
 
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