If we're talking relative values... can I bring this onto a table top with a light source behind a diffuser and simply put the light meter on the other side of the lens?
If we're talking relative values... can I bring this onto a table top with a light source behind a diffuser and simply put the light meter on the other side of the lens?
Sure. Just make sure the light is very diffuse and uniform over the viewing area.
In fact, a defocused subject will give you more uniform illumination than a focused subject,
unless the subject has a very uniform tone and reflectance to start with (like a gray card).
- Leigh
If you believe you can, or you believe you can't... you're right.
If you believe you can, or you believe you can't... you're right.
I'd think it would work fine with both lenses at infinity focus.
Focus point (i.e. bellows extension) is irrelevant if the two lenses have approximately the same FFL.
Even a 10mm difference in FFL should result in <1% error (approximation) for lenses in the focal length under discussion.
If the lenses have disparate focal lengths, then yes they should be focused at infinity for maximum accuracy.
BTW, this does not mean that the test target/subject needs to be at infinity, as discussed above.
- Leigh
If you believe you can, or you believe you can't... you're right.
If both lenses have nearly identical focal distance then, yes, bellows extension is irrelevant. No, the target need not be near infinity focus. In fact, I'd place it very near the lens(es) with them focused at approximately infinity just to blur the target.
Dan,
Have you been drinking?
T-stops are just accurate apertures, used because they want extremely accurate exposures.
They DO NOT measure luminance at the film plane, as I've suggested for this application.
- Leigh
If you believe you can, or you believe you can't... you're right.
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