Greg and others,
I will validate Photosphere and thought about the following testing parameters:
matte saturated colored samples
matte Munsell gray cards
variation of f-stop from 2.8 to 8 (min and max on my digital camera)
incandescent vs. fluorescent vs. daylight (daylight is tough as it varies)
on-axis vs. 40 degrees off axis
colored and gray cards on black vs. white background
sample size around 4 X 4 cm^2 photographed at a distance of 5 meters or so
tested against spot luminance meter 1 degree
Any other suggestions?
Martin Moeck
Hi Martin,
matte saturated colored samples
Don't expect good results, but this is definitely worthwhile.
matte Munsell gray cards
variation of f-stop from 2.8 to 8 (min and max on my digital camera)
You should combine this with the off-axis tests, since vignetting is known to increase at larger apertures. You can actually plot the fall-off as a function of angle from the image center and fit a curve to it for each f-stop. This can then be applied as a correction using pcomb.
incandescent vs. fluorescent vs. daylight (daylight is tough as it varies)
You can use different color-balance fluorescents instead of relying on daylight.
on-axis vs. 40 degrees off axis
colored and gray cards on black vs. white background
sample size around 4 X 4 cm^2 photographed at a distance of 5 meters or so
tested against spot luminance meter 1 degree
The flare measurement we just performed on our camera is one I recommend. Start with a uniform light source, such as a fluorescent fixture with a good diffuser. Capture an HDR image of it, and take a luminance reading at its center. Then, cover it with a black posterboard with a small hole cut in it and capture an image of the hole using exactly the same settings. If the camera lens is perfect, the measurement of the hole should match the original uniform field. It will be lower, and the difference is due to scattering in the lens.
-Greg