Scanner with shallow depth of field

[Steve]

I'm looking for a scanner with a shallow depth of field. Objects 1/4
inch away and further from the top glass surface need to be completely
out of focus. The desired focal plane would be about 1/8th inch away.

The application is to acquire images of crystals formed in a solution
held in a small tube placed on the scanner. There are multiples of
these tubes held within a plate that need to be acquired all at once.
The tubes have caps that must be out of focus or else they obscure the
image. I have tried a Microtek ScanMaker X6 but its depth of field is
too large such that the caps are visible in the image.

Individual tube bottom diameter is 3/16 inch. The overall size of the
plate holding the multiple tubes is 3 x 2 inches. This large overall
size has prevented use of a camera due to the resulting large depth of
field at such a large field of view. A macro or close up camera with
shallow depth of field does not have the ability to acquire the
multiple tubes at once.

 

[Neil Gould]

I'm looking for a scanner with a shallow depth of field. Objects 1/4
inch away and further from the top glass surface need to be completely
out of focus. The desired focal plane would be about 1/8th inch away.

The application is to acquire images of crystals formed in a solution
held in a small tube placed on the scanner. There are multiples of
these tubes held within a plate that need to be acquired all at once.
The tubes have caps that must be out of focus or else they obscure the
image. I have tried a Microtek ScanMaker X6 but its depth of field is
too large such that the caps are visible in the image.

Individual tube bottom diameter is 3/16 inch. The overall size of the
plate holding the multiple tubes is 3 x 2 inches. This large overall
size has prevented use of a camera due to the resulting large depth of
field at such a large field of view. A macro or close up camera with
shallow depth of field does not have the ability to acquire the
multiple tubes at once.

I don't think you'll have much luck with a flatbed scanner. I don't know
what kind of camera you've tried, but 3x2 inches is not too large for
macro photography with the right setup. The depth of field will depend on
the lens used and exposure required. If I'm picturing your subject
correctly I would go with a mid-telephoto and extension tubes or bellows
to get this shot.

Neil

 

[Chuck Tribolet]

I'm not sure you can get THAT small of a depth of field. You're going
to need a very fast lens.

A camera with a macro lens would definitely get the 3x2 area. I'd
recommend the Nikon 105 mm macro lens. They are very common --
ask around, you probably have a friend with one. Shoot wide open.
If that doesn't work, ask around for a fast prime lens. Nikon and
Canon have both made 50mm-ish f/1.4 lenses (fairly common in
the old days of slow film -- I have one somewhere), and I think they
both made an f/1.2 (expensive and uncommon), and somebody made an f/1.0

 

[Neil Gould]

I'm not sure you can get THAT small of a depth of field. You're going
to need a very fast lens.

It's difficult to know how small "THAT small" is without more specifics,
but from Steve's description I was guessing that about a 1" depth of field
with the 3x2" plane of focus is what he's after. This is achievable with a
short tele & extension tubes or bellows. It might not be as easy to
accomplish this with a fixed macro lens. The point is that a scanner is
not the best tool for this task.

Regards,

Neil