I recently got a betterscanning film holder. I am using it in the dry mounting mode. I tape the emulsion side of the film to the dull side of the holder glass and place the glass in the frame with the film base facing downard towards the scanner glass.
I've been trying to determine the optimal height over the scanner glass. I've scanned 4 x 5 Ilford HP5 negatives with the frame at 0.0, 0.2, 0.4, 0.6, and 0.8 mm above the scanner glass, and so far I can't see any differences in how sharp the image is. The images are not quite as sharp as what I can see looking at the negative on a light table under a loupe, but they are all pretty close to that.
It may just be that images formed on HP5 film with my camera and lenses is not going to show enough detail for me to see any differences in that range. But I think my scans capture enough detail to look quite sharp in prints at normal viewing differences. It may also be that there is something else I don't understand.
It would help me if I had some idea of how the optics of the V700 work. The negative image could be considered a subject which the scanner is taking a picture of with its optical system. So there must be something we can call depth of field, i..e, a range of distances the negative can be in which will produce essentially the same result given the capability of the scanner. It would help me to know what to expect if I knew what that range might be.
The scanner is capable of scanning at 6400 ppi, although I don't know if it actually does that for a 4 x 5 negative. I believe it can capture that many pixels, but I don't believe the scanner can resolve that well, which would amount to 1/2 x 6400/25.4 = 126 lp/mm. In my trials I am scanning at 3200 ppi, which would provide 63 ppi, and I doubt it it can actually do even that. I would be surprised if it can even provide 40 ppi optical resolution.
So I would appreciate anything anyone can tell me about the optical performance of the Epson V700 and how that might affect the tests I am doing. How far will I have to raise the frame above the glass before I see degraded performance with typical large format negative films. Also, can anyone suggest another source to scan which will have enoough fine detail to allow me to see a progression?
Anything else of course would be of value.