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Is your ISO off on your Digital SLR?
Old 04-25-2007, 08:16 PM   #1 (permalink)
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Hi everyone, I saw Tim Meyer speak at a local event and he had mentioned that his ISO was off on some of his and on some of his students. In some cases up to 2 stops off. He proposed a way to test it. But that info was only for those of us that bought his $2500 seminar lecture series. Anyway, have any of you had problems with the ISO being off. How can I test that? Thank

JP
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Re: Is your ISO off on your Digital SLR?
Old 04-25-2007, 09:10 PM   #2 (permalink)
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Originally Posted by Jaen_Paul View Post
Hi everyone, I saw Tim Meyer speak at a local event and he had mentioned that his ISO was off on some of his and on some of his students. In some cases up to 2 stops off. He proposed a way to test it. But that info was only for those of us that bought his $2500 seminar lecture series. Anyway, have any of you had problems with the ISO being off. How can I test that? Thank

JP
1. One easy way is to put the camera in P mode and set the ISO to 100 and then shoot a shot of a gray card (full frame - fills the view finder). This should give you a single spike on the histogram at about center if your in camera meter is right on. No matter what it gives you, note the shutter speed and fstop.

2. Set the camera to manual. Set the camera to the noted shutter speed and fstop.

3. Adjust the fstop or shutter speed and shoot the gray card again. In this phase you're just making adjustments until the full frame shot has a single spike in the middle of the histogram. Now we know we have a right on exposure at ISO 100 for the gray card.

4. Now change the ISO to 200. Shoot the gray card again. What should happen to the spike? It should move to the right? Why, because we've doubled the ISO? What do we need to do to move it back to the center? Right, we need to stop down by 1 stop. Do that. Shoot again. Is the spike back in the center? If so, then ISO 200 must be accurate. Now go to ISO 400 and repeating the same logic we would have to adjust the fstop by stopping down 1 stop.

So here's how it worked in my test:

iso 100 1/15th at f2.8
iso 200 1/15th at f4
iso 400 1/15th at f5.6

and so forth.

What if the above doesn't work out? Well then you have a problem somewhere?

Personally I've never had that problem or known anyone that has. But if I was selling a $2500 seminar package, I might be able to find some people with that problem!

Cheers,
rfs
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