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by evan-pak

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How can I find a modern flatbed scanner with a reasonably large depth of field? Here "reasonably large" would be something like at least 2mm of DoF above the scanner glass.

Typically DoF is not listed anywhere in the technical specification, and few people are interested in testing it when they are reviewing a scanner.

Based on what I have learned so far, it seems that older scanners often had a fairly deep DoF. For instance, my old (> 10 years) HP ScanJet 4200C performs reasonably well.

However, many modern scanners seem to have an extremely shallow DoF. My guess is that this is related to the fact that older scanners used a CCFL lamp while a modern scanner often uses LEDs. With LEDs, the scanner can be made much thinner. Perhaps the small physical size of the scanner favours a lens that has a shallow DoF?

But this is just a guess, as I don't really know anything about the construction of the "lens" that is used in scanners. Can one somehow explain it in "SLR terms"? Does it make sense to use terms like focal length and aperture in the context of a scanner?

Some background: I am abusing my scanner as a digital camera; I use it to take pictures of nearly flat objects. For example, if you need a quick snapshot of a handmade greeting card (flat decorations glued to a cardboard background, etc.), a scanner is surprisingly convenient in comparison with a DSLR: you don't need to worry about aligning the camera perpendicular to the object or setting up lighting, and you won't have any lens distortion that you need to fix in post.

However, this is possible only if the scanner has enough depth of field above the glass.

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I'm gonna go out on a limb here and say "taking pictures" of flat objects is kind of the definition of a scanner - I'd not call it "abusing" it. – rfusca Apr 11 '11 at 22:24
@rfusca - yes, but he said nearly flat... ;-) – ysap Apr 11 '11 at 22:30
Have you tried the HP Scanjet 4670 See-Through scanner? It is supposed to let you take pictures of objects by simply placing the scanner on top and as such is not expected to be perfectly level... I can't confirm this though, only that I read it somewhere. – Itai Apr 11 '11 at 23:23
@Itai: Thanks, I haven't tried it, but this review (see the very end) suggests that the DoF isn't particularly large. However, no real DoF measurements here either. – Jukka Suomela Apr 12 '11 at 8:07

I'm aware of at least one 3D scanner manufactured by HP called "Top Shot". It uses an array CCD instead of a linescan CCD + scanning mechanism, so it should also capture images faster, although the effective resolution is likely not quite as high as a traditional flat-bed scanner. The downside/upside (depending on your needs) is that the scanner is part of an all-in-one printer.

I've casually played with one and came away impressed, but I don't have any in-depth experience with the product.

Here's a link:

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Using a scanner as a camera is no abuse at all, Scanography is certainly photography and arguably an art form.

In order to achieve the necessary DoF, you will need a scanner with a CCD sensor. The newer (and thinner) ones use a CIS sensor and thus have a very shallow DoF. Just keep in mind that most CCD scanners are going to be more expensive.

You may want to check Robert Louis Fleming's blog, for a lot of interesting approaches to scanography and his quite beautiful results.

There's also a short tutorial for scanography on PhotoGalaxy

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There are scanners that are advertised as having 3D object scan ability. A search at Google came up with an example. I believe the DoF should be deep enough for your needs.

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Thanks, this part looks promising: "You can even scan three-dimensional items up to approximately one inch thick". However, this seems to refer to the physical design of the lid, not the DoF. Did you find any information on DoF? – Jukka Suomela Apr 12 '11 at 7:58
@Jukka - No, I did not, but my interpretation is that they refer to the actual ability to scan non-flat objects, but I may be wrong. – ysap Apr 12 '11 at 8:02

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