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View Full Version : How do I calibrate D70 exposure ??



Jeff Selles
01-28-2005, 08:23 AM
I have a D70 and I'm stumped on how to calibrate the exposure.
Specifically, when I shoot an entire black surface in any mode, D70 pushes the exposure into the white zone, not grey ??

When I shoot an entire white surface or 18% grey card, the same thing happens. The exposure is automatically pushed into white. I'm doing this because I want to determine where the 18% grey card shows up on the camera histogram. I've never seen a camera like this. The Canon 20D adjusts 100% black, white, or grey cards to the exact same grey zone on the histogram just as expected !

- Jeff :confused:

jaykinghorn
01-28-2005, 10:38 PM
Jeff,

It sounds to me like you are using an auto-exposure mode (P, A, or S). It also sounds like the camera may not be metering for Zone V midtones, but to a Zone VI midtone (1-stop brighter, better match for caucasian skin tones) When you say white are you talking about RGB values in the 175 range, 200 range, 255 range? A little more information would be helpful in diagnosing your problem. It may be that you have an incorrect setting somewhere that is automatically overexposing your images two stops.

Best regards,
Jay Kinghorn
RGB Imaging

Samuel Lo
01-31-2005, 09:28 AM
Jeff,

It sounds to me like you are using an auto-exposure mode (P, A, or S). It also sounds like the camera may not be metering for Zone V midtones, but to a Zone VI midtone (1-stop brighter, better match for caucasian skin tones) When you say white are you talking about RGB values in the 175 range, 200 range, 255 range? A little more information would be helpful in diagnosing your problem. It may be that you have an incorrect setting somewhere that is automatically overexposing your images two stops.

Best regards,
Jay Kinghorn
RGB Imaging

Wait, I can't get it. Jay, can you explain a little bit more please? What is Zone V & VI midtone and 175 range?

Thanks.

Samuel :confused:

DownByFive
01-31-2005, 08:36 PM
I've read that the in camera histogram only shows the green channel...Maybe that's something to think about. But that may be incorrect...

jaykinghorn
02-01-2005, 05:52 PM
Sorry, for jumping ahead. Traditional black and white photography based exposure on the Zone System. Zone I is maximum black (without detail) and Zone X is paper white (without detail). Zone V is 50% gray. Most cameras attempt to average the scene based on the assumption that the scene will be of averate reflectance (zone V). This means that if you are shooting a black sheet of paper, the camera will naturally try and expose so that it is gray. Likewise with a sheet of white paper. I doesn't sound like this is actually what is happening with your camera.

A more likely culprit is the over/underexposure adjustment. Most cameras allow you to specify that the camera add or subtract exposure from the meter reading. This is used to compenste for the camera's tendency to render everything as 50% gray. So, for a black piece of paper you would subtract 1 1/2-2 stops of exposure so that the black paper is correctly rendered as black. Conversely, you would add 1 1/2-2 stops of exposure so that the white paper is white in your image. It sounds to me like you may have the camera set to automatically overexpose all of your images.

I hope this helps.
Jay Kinghorn
RGB Imaging