Soft scans or soft images?

[walter23]

Attached is a pretty typical transparency scan (in terms of sharpness). Scanned at 1200 DPI on my epson V750. Second is a full 1200 DPI crop. Is this normal for this kind of scan? I'd like to get slightly sharper results, but I can't decide if my in-camera technique (or lenses) are failing or my scanner is at fault. It just seems to me that these shouldn't really be falling apart at only 1200 DPI.

I can think of a couple of very obvious variables in camera that could lead to soft images. 1. I use a fairly stiff cable release and my exposures often end up being 2 second "T" exposures. 2. I stop down to f/45 or f/64 for a lot of my shots to ensure adequate depth of field but could diffraction be the cause? 3. Lens sharpness? (caltar II-N rodenstock lenses - 90 and 210 at the moment).

The conundrum is that I have to examine my transparencies with my scanner. I'm happy with the sharpness of my 11x14 and 16x20 B&W prints from the darkroom; I just haven't printed any colour yet (nothing I'm happy enough with to print).


(No criticism on the aesthetic of the image please. It's not a good shot, I know. Just happened to be convenient for this)

[Rob Champagne]

an inch on your screen will be something like 96dpi. An inch in a print is something like 360dpi or maybe 720dpi. That means looking at it on screen is roughly equivalent to a 4 times (or 8 times depending on your chosen print resolutoin) enlargement to how it will look when when printed. Given that scans will be a little soft anyway and your aperture sounds to be a little small for optimum sharpness and your lens may not be the sharpest out there, then it is hardly surprising that what you see on screen is not sharp. It never will be. Just how unsharp is depnds on above factors.
You best option is to print a small test patch and judge that and not your screen image.

[Rob Champagne]

and when you scan at at 1200dpi when your flatbed scanner is capable of much higher resolution, you leave big gaps between each dot which ruins the sharpness. The dot size is not variable on a flatbed in the same way it is on a drum scanner.
Scan at native scanner resolution and then downsize by factors of 2 to get to where you want to be.

e.g. say you want to make a 16x20 print printed at 360dpi. Your file size needs to be 5760x7200pixels.

at the scanners 4800dpi setting, that gives you a file size of 19200x24000. So first downsize would be to 11520x14400 (twice final size) and the second downsize would be to 5760x7200.
Apply a little sharpening before each dowsize. I use 50% 0.7 others mileage may differ and some do the downsize in one go. The downsize loses many small scan artefacts and tiny dust specs. Best to spot it before the first dowsize and don't don't sharpen after last downsize unless you really need to.

Now I can hear you say, but I don't have the RAM for this and it takes a long time for the scan. Well if thats the case, then why didn't you buy a scanner with a larger scan dot size which equates to a lower resolution scanner, because by buying that top of the line epson and not scanning at its native resolution, you are throwing away its capabilities.

[walter23]

Are you saying the scanner doesn't sort of downsample on the fly but rather just discards every nth pixel in its linear sensor?

[Rob Champagne]

Yup! If it were downsampling it would be even slower. But usually when you scan at lower res its a hell of a lot faster which wouldn't be the case if it were scanning at native resolution and then doing the additional process of downsampling.

[walter23]

If the scanner firmware did the downsampling before sending the data to the computer you'd avoid the communication bottleneck which might account for the speed increase... but I'll give your suggestion a try. It rings true because I've noticed that my higher resolution scans look better (and not just because of the obvious higher resolution). I figured maybe it was switching to a different sensor or optics (based on something someone once said on a forum I think), or maybe using finer control over the stepping motor. But when I think about it those explanations don't make much sense.

[Rob Champagne]

For absolute best print quality scan at 6800dpi and adjust print dpi only to obtain print size you want. i.e. no downsize. The higher print res will compress more dots into an inch and retain more original fine detail. I know some people will say you can't see the difference but I urge you to try it if you have the memory available to do it.

[Greg Lockrey]

This has be very enlightening, Rob. I'll have to look at my film scanning with the 750V differently from now on.

[Aender Brepsom]

Rob, shouldn't you be nicknamed "An old dog teaching new tricks"?
I'd like to thank you for the precious information. I guess they are valid for other flatbed scanners too. I'll have to try it.
Really helpful! Cheers

[Ted Harris]

I have to disagree with scanning at 6800 spi. It is pure overkill and what you are actually doing is sapling a lot of data that contains no information. The problem being that the true optical resolution of this scanner is more like 2200 spit according to our tests and the tests of others. So, if you sample at 2400 spi you are capturing all the information on the film. Not to mention that a 6800 spi scan of a full frame 4x5 tranny will give you a really huge file that you will find difficult to impossible to manipulate unless you have a powerful computer system. In fact, when I tested this scanner when it first came out I did try some scans at 6800. Tried some specifically on a MacBook with 2 GB of RAM to see what would happen ... the system consistently crashed. When I scanned on the G5 Tower with 5 GB of RAM all was well if awfully slow.