How sensitive is the Epson V700 to source height above glass?

[Leonard Evens]

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.

[biedron]

Leonard,

check out post 7 in this thread:

http://www.largeformatphotography.in...canner%20focus

Bob

[Leonard Evens]

Leonard,

check out post 7 in this thread:

http://www.largeformatphotography.in...canner%20focus

Bob

I see now why I don't see any differences. I would have to start well over 1 mm and go upp in step of .4 mm before I would start to dee any differences.

But I also clearly need a source with finer resolution.

[D. Bryant]

I see now why I don't see any differences. I would have to start well over 1 mm and go upp in step of .4 mm before I would start to dee any differences.

But I also clearly need a source with finer resolution.

See if you can source a high contrast focus negative. This will make your height adjustment a little easier.

[Heroique]

...It would help me if I had some idea of how the optics of the V700 work...

Leonard, keep in mind that selecting “Film (with film area guide)” activates the lower resolution lens; selecting “Film (with film holder)” activates the higher resolution lens. Typically, the two lenses will have two different optimal scanning heights. (These options are inside the “Document Source” box, for Epson Scan.)

Note to 4990 users: strangely, you also have these options, but the 4990 has only one fixed lens, so it doesn’t matter which option you pick.

[Leonard Evens]

Leonard, keep in mind that selecting “Film (with film area guide)” activates the lower resolution lens; selecting “Film (with film holder)” activates the higher resolution lens. Typically, the two lenses will have two different optimal scanning heights. (These options are inside the “Document Source” box, for Epson Scan.)

Note to 4990 users: strangely, you also have these options, but the 4990 has only one fixed lens, so it doesn’t matter which option you pick.

I work under Fedora Linux, so I can't use the Epson software. I use Vuescan, which I think is superior anyway. I don't know how Vuescan selects the lens to use. I presume it is based on the scan resolution chosen.

[SergeiR]

I work under Fedora Linux, so I can't use the Epson software. I use Vuescan, which I think is superior anyway. I don't know how Vuescan selects the lens to use. I presume it is based on the scan resolution chosen.

it gives you weird option with v700 of regular negative and 8x10 negative

[genotypewriter]

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.

Try the maximum height and the minimum height and one in between. If you do this in a strategic way, you can narrow down on the height that gives the best height fairly easily.

One thing I've noticed with the V700's focus is it comes to a point where you're balancing between low CA and sharp focus. But at that resolution (6400 PPI) the image is not something you'd want to view at 100% anyway.

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.

Don't be too quick to blame the scanner. At 6400 PPI diffraction starts to set in at f/5. So you need to have a lens that resolves 126 lp/mm at f/5 or faster. Not many 4x5 lenses are up to that:

http://www.flickr.com/photos/genotypewriter/6806479707

And not many people shoot faster than f/5 on LF to begin with...

In all fairness, 6400 PPI is equivalent to a 54.8 megapixel full frame 35mm sensor (the current state of the art/D800 is 36.3) ... even if the whole capture process was digital and five-$-figure DSLR lenses were used, you're not going to be seeing many 1 pixel wide details So the V700's pretty awesome in what it does for a few hundred $.

[Leonard Evens]

I've now done 0.8, 1.6, and 2.4, i.e., one, two, and three full turns from base. (I tried to measure the extensions of the white screws with a dial caliper, and I don't get those measurements, but I will use the figures given by betterscanning.) They get progressively sharper. I am not sure what to do now, since there isn'tt much further I can go with the screws provided by betterscanning. The reference provided above showed the optimal distance to be 3.2 mm. I may be able to get that high by one last full turn of the screws, but the support is likely to be pretty wobbly. Also, I won't be able to go beyond that to determine what my optimum is if it is a bit hgiher.

Any suggestions?

[Leonard Evens]

I've now done 0.8, 1.6, and 2.4, i.e., one, two, and three full turns from base. (I tried to measure the extensions of the white screws with a dial caliper, and I don't get those measurements, but I will use the figures given by betterscanning.) They get progressively sharper. I am not sure what to do now, since there isn'tt much further I can go with the screws provided by betterscanning. The reference provided above showed the optimal distance to be 3.2 mm. I may be able to get that high by one last full turn of the screws, but the support is likely to be pretty wobbly. Also, I won't be able to go beyond that to determine what my optimum is if it is a bit hgiher.

Any suggestions?

It is not as bad as I thought. I forgot to take the thickness of the support for the glass in the film holder into account. It added more than a mm to the overall height.

So my last measurment was in fact at about 40 mm above the scanner glass. I've now also tried going down to about 36 mm above the scanner glass, and I can't see any difference from 40 mm. I think the optimal height is between 30 and 40 mm, as noted in the above reference. I may do some more measurements, but if I leave it at about 36 mm, I think it will be more than good enough for scanning 4 x5 negatives.