Colour fringing with V750?

[walter23]

Before I go too far with this, I want to put this into some perspective. I've made beautiful prints from scans with this scanner, at pretty big sizes. I'm just nitpicking and trying to optimize things at this point. Now, on to the question:

Do you guys get noticable colour fringes with your V750? I find these if I scan B&W film in colour mode, etc, at high resolution (~4800 DPI).

This is from a 6x4.5 transparency scan, but I've seen it in detailed crops from 4x5 and 35mm, B&W and colour, both with silverfast and epson scan.

Resized:



Detail (6400 DPI), but also shows up in 2400 DPI scans:



Note the red border along the buildings. This sometimes happens normally with lenses on cameras due to the different wavelengths of light refracting differently through the lens, but in a scanner is this normal or defect? Is there anything I can do to reduce its appearance? Is it an issue of focus? It's not the camera; it appears in scans of B&W negatives if I scan in colour (red fringes on one side of high contrast lines, blue or yellow (can't remember) on the other), and seems to contribute to softness in B&W scans (again, for some perspective, I'm talking at ridiculous enlargement. I've printed 8x10s from 6x4.5 scans that look great).

[Walter Calahan]

The best test is to scan this image on someone else's V750 to campare notes. It might be you've found the limit of this machine. I own a V750 and haven't notice, but then I'm not looking so extremely. Good luck and let us know what you find if you can test on another scanner.

[Doug Fisher]

FWIW, I have experienced this and have had others contact me with the same experience. The has happened scanning on the glass, using the holders, with and without using anti Newton glass, so it can be quite variable/random. Sometimes you can scan a second time without changing anything and not get the problem. Other times, you can just change the orientation of the film ever so slightly and the problem will go away. Others have minimized the problem by flipping the film over and scanning (then re-flipping in Photoshop). I have seen this issue on scans made from a 3170 all the way up to the V series. Some scanners brands may be better than others but this issue isn't limited just to Epson scanners.

Doug Fisher
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www.BetterScanning.com

[walter23]

Okay, thanks Doug. I did have the impression that it was sort of variable (I was pretty sure that I rescanned the same B&W film twice and had it appear and then disappear). At least I won't worry that it's doing anything unusual.

[Kirk Gittings]

I think that much CA would only be visible in a 40x60 print. As far as the CA goes, how do you determine if it is in the film, i.e. CA from your camera lens, vs. the scanner lens?

For those scanning b&w in RGB then dumping all but the sharpest , least noisy channel, usually the green channel, the CA will not be an issue.

[walter23]

I think that much CA would only be visible in a 40x60 print. As far as the CA goes, how do you determine if it is in the film, i.e. CA from your camera lens, vs. the scanner lens?

That's a good point and one that I've considered, but as mentioned it shows up with variable intensity (with scans of the same slides), and more importantly, in B&W negatives scanned in colour. I've also compared a photograph taken with my digital SLR + macro lens to a scan of approximately the same film dimensions and the CA shows up in the film scan but not the macro photograph.

It's not such a big problem that I regret this scanner, but I do want to optimize my workflow to avoid it if that's possible (or exchange it if its a defect with my scanner, which appears not to be the case). I did wonder whether it was an issue resulting from lack of film flatness or bad focus, which I still haven't ruled out (though Doug's response suggests its not).

[Greg Lockrey]

For those scanning b&w in RGB then dumping all but the sharpest , least noisy channel, usually the green channel, the CA will not be an issue.

I've seen other folks talk about copying B&W in RGB and the "dumping" all but the green channel to get the sharpest image. At what step is this done? IE in the scan set up or later in Photoshop?

[Ted Harris]

Greg, it's done in PS.

[Michael Mutmansky]

CA is an issue all the time. Color Fringing will not be an issue with a B&W scan when done as Kirk describes.

The problem with CA is that it is in the source material, and so it will impact the scan, even if it is for a B&W image. Color Fringing (for want of a better term, that's what Ted and I have come to call it) is a result of (probably) parallax errors in the optical system. The are always predominately in one direction in the scanner and not in the other.

If you want to determine whether it's the scanner or the source, rotate the source and rescan. If the fringing appears to change it's preference (which side the magenta or green favors) then you have a problem with CF, not CA. If it remains the same, it is CA in the source. Most likely, you have a combination of both here, which will confound the issue a little.

This looks to me to be more of a CA problem, because the color fringe appears to be about the same on both axis of the building, and that is not how I see color fringing in the scanner normally happening.


---Michael

[Greg Lockrey]

Thanks Ted. I don't play with B&W that often but I thought that it would be a good thing to know.