ASA/ISO For Canon XL1s

Bill Ravens · July 25th, 2002, 08:02 AM

You're right on, Jeff. CCD's have much less "latitude" than film. That's why they blow out the highlights and muddy up the shadows so much more easily than film. Off of ideal exposure, we pay the price. In any given scene, the range of light to dark values may exceed the CCD's ability to respond linearly. That is to say a CCD is not as forgiving of contrasty scene conditions as film.

Jeff Donald · July 25th, 2002, 08:11 AM

The contrast range could be measured too, using a grey scale like in the Zone System. I did all this 20 years ago when I shot out West with my 4x5. I don't know if I have a good grey scale any more, but I still have my densitometer. This might turn into a real challenge. This will take some thinking.

Jeff

Don Palomaki · July 25th, 2002, 04:20 PM

The major reason for use of light meters with film is that there is no instant feedback to judge exposure. The video camera gives real time feedback as to exposure on the monitor or viewfinder. Zebra helps judge highlight exposure.

Thus a light meter is mostly useful for judging set lighting (e.g., lighting uniformity) before the videocamera arrives.

The 18% gray card means that no reflected (short of a mirror-like reflection of a lamp) highlight will be more than about 2.5 stops brighter (100% reflectance). This concept works well with the way film speed is rated and the typical exposure latitude of film.

Because CCD's have a different response (exposure latitude if you will) than film, the 18% setpoint for exposure will not yield the same relationahip between shadow and highlight detail and the primary items of interest in the scene (the reference to blownout highlights and muddy shadows).

Also, when playing wiht light meter readings, keep in mind that as processing is also a factor in film speed so gain is with video. With video 'gain' corresponds to push (or pull) processing. So check your gain setting as wellas the aperture and shutter speed. 6 dB of gain corresponds to a stop of push processing.

Jeff Donald · July 25th, 2002, 05:05 PM

I'm sure i could amass a large amount of data but to what point would it be useful. Whenever possible, I try to use a waveform/vectorscope. It tells me a whole lot more than a simple light meter does. However, when I'm in the field a waveform/vectorscope isn't feasible. I depend on the zebra pattern now to aid in exposure (and 20 years experience in the field). But at times, I miss, and end up with shadows crushed or worse, highlights blown out. it would be nice to spot meter a highlight and accurately place it in a zone. But i don't think that's going to happen.

Jeff

Bill Ravens · July 25th, 2002, 06:14 PM

Jeff...

For awhile, I tried using the Zone System. I found that my outside, naturally lit scenes changed too rapidly. The system works well indoors when setting up lighting, however. Indeed, the best overall system is the zebra display, I set mine to 90% which gives me about 10% headroom. When I get to my NLE, I might "tweak" certain selected groups of frames using a signal analyzer. Generally, correcting overexposed scenes works better than correcting underexposed scenes. Expose for the highlights and let the shadows fall where they may.

July 25th, 2002, 08:02 AM	#16
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	You're right on, Jeff. CCD's have much less "latitude" than film. That's why they blow out the highlights and muddy up the shadows so much more easily than film. Off of ideal exposure, we pay the price. In any given scene, the range of light to dark values may exceed the CCD's ability to respond linearly. That is to say a CCD is not as forgiving of contrasty scene conditions as film.

July 25th, 2002, 08:11 AM	#17
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	The contrast range could be measured too, using a grey scale like in the Zone System. I did all this 20 years ago when I shot out West with my 4x5. I don't know if I have a good grey scale any more, but I still have my densitometer. This might turn into a real challenge. This will take some thinking. Jeff

July 25th, 2002, 04:20 PM	#18
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,489	The major reason for use of light meters with film is that there is no instant feedback to judge exposure. The video camera gives real time feedback as to exposure on the monitor or viewfinder. Zebra helps judge highlight exposure. Thus a light meter is mostly useful for judging set lighting (e.g., lighting uniformity) before the videocamera arrives. The 18% gray card means that no reflected (short of a mirror-like reflection of a lamp) highlight will be more than about 2.5 stops brighter (100% reflectance). This concept works well with the way film speed is rated and the typical exposure latitude of film. Because CCD's have a different response (exposure latitude if you will) than film, the 18% setpoint for exposure will not yield the same relationahip between shadow and highlight detail and the primary items of interest in the scene (the reference to blownout highlights and muddy shadows). Also, when playing wiht light meter readings, keep in mind that as processing is also a factor in film speed so gain is with video. With video 'gain' corresponds to push (or pull) processing. So check your gain setting as wellas the aperture and shutter speed. 6 dB of gain corresponds to a stop of push processing.

July 25th, 2002, 05:05 PM	#19
Jeff Donald Warden Join Date: Mar 2002 Location: Clearwater, FL Posts: 8,287	I'm sure i could amass a large amount of data but to what point would it be useful. Whenever possible, I try to use a waveform/vectorscope. It tells me a whole lot more than a simple light meter does. However, when I'm in the field a waveform/vectorscope isn't feasible. I depend on the zebra pattern now to aid in exposure (and 20 years experience in the field). But at times, I miss, and end up with shadows crushed or worse, highlights blown out. it would be nice to spot meter a highlight and accurately place it in a zone. But i don't think that's going to happen. Jeff

July 25th, 2002, 06:14 PM	#20
Bill Ravens Join Date: Nov 2001 Location: santa fe, nm Posts: 3,264 Images: 10	Jeff... For awhile, I tried using the Zone System. I found that my outside, naturally lit scenes changed too rapidly. The system works well indoors when setting up lighting, however. Indeed, the best overall system is the zebra display, I set mine to 90% which gives me about 10% headroom. When I get to my NLE, I might "tweak" certain selected groups of frames using a signal analyzer. Generally, correcting overexposed scenes works better than correcting underexposed scenes. Expose for the highlights and let the shadows fall where they may.