DOF in photomicrography

[P3D David C. Glick <xid@xxxxxxx>]

Sam Smith wrote:
>On a similar topic,is there any practical way of resolving the DOF problems
>when shooting through a microscope? 

Hi Sam,

Yes, there are at least a couple.  Oh-- you said practical.  In that case
skip to the next paragraph.   An expensive way is confocal microscopy, which
can function in various modes.   As I understand it, light rays from the
out-of-focus part of the image are excluded; the system can then be focussed
at successive levels within the specimen, each in-focus partial image
acquired, and the images then composited to get a whole, in-focus image.
There's an explanation at http://www.cs.ubc.ca/spider/ladic/intro.html which
is specific to laser scanning confocal microscopy.  I'm not sure whether any
of the variations allow direct-to-film photography or if an electronic
intermediate is always required.  I just did a search for some web sites and
found one with anaglyph stereo images:
http://axon.med.ohio-state.edu/cmif/confocal.htm  and
http://www.zeiss.de/mi/contacts/ecc_cam/ECCLSM.html also has a bunch of links.

A simpler method was written up several (6-8?) years ago in a magazine that
our staff photographer got -- Photomethods?  Since then I've tried without
success to find that article again, although I have seen the same topic
elsewhere.  I don't remember its proper name.  It should work for micro or
macro methods.  It illuminates the subject from the sides (in a plane
perpendicular to the optical axis) using a slit aperture on the light
source.  This is set to illuminate only the depth of the subject that is in
focus; the rest of the subject is not illuminated and does not expose that
area of the film.   The exposure is made, the focus is moved and the
illuminating aperture moves with it, another exposure (or maybe a continuous
exposure) is made on the same film, and so on, building up a complete
in-focus image on film.  They had some good examples in the article.  Of
course the subject has to be motionless while all this happens.  

Does anyone have any more practical ideas?

Dave Glick


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