First, it's the 20Da.

Second, it costs over twice as much as the 20D.

Third, it needs to be fitted with an IR filter for most uses; it is
optimised for astrophotography and in particular the H alpha IR light.

Fourth, Canon state the live preview is only for use with very dim
images; I have not seen any information confirming that it can be used
in this application (though it would be very good to have it so
confirmed).

To the OP

You will find more information on the web if you search using the
correct term, photomicrography. SLRs of any kind (digital or film) are
not necessarily the best devices to use for PM work. However, they are
perfectly practicable.

The Canon 10D and 20D are satisfactory; they have mirror lock-up (which,
as you suggest, is essential) and they will meter quite happily when
used without a lens fitted. They use a CMOS sensor which has a very good
low noise performance. I have used my 10D with extreme ND filtration and
30 second exposures to test this, and the images are perfectly usable.
If you are on a tight budget and don't particularly need to use the DSLR
for non-PM work, then the 10D has more resolution than you will be able
to get from your microscope, and a second hand one will be half the
price of a 20D. The 20D will wildly oversample the image and waste
resolution.

The main drawback I find with a DSLR on a microscope is focussing. The
focus screens on most AF cameras are very poor for manual focussing;
even using a Canon right-angle finder with 2.5x magnification it is not
easy to get really spot-on focussing. In many ways a good compact is
easier to use and will give equally good results in most circumstances.
I use a Nikon Coolpix 995; the later 4500 may be better (4MP). This
family is very popular in the PM community, and you will find plenty of
information on the web about using them on a microscope. The video
output is very useful for focussing.

Tell us what kind of subjects you will be using it for, and what you
want to do with the output and we can maybe give more specific help.

Also, you will find far more expertise in sci.techniques.microscopy and
the Yahoo Microscopes group.

David

That's 20Da.  It's a 20D, hence the D in the Da, with astrophotography
features.  Christ, it shows the D in the headline of the article you
posted the URL to.

Gregh

It's resolution and sensor size would make it the ideal microscopy
camera.
-Rich

I did some tests with my 10D at ISO 1600 and using a crossed polariser
attenuator to give 30 second exposures. Some of the images were placed
in my folder on the Yahoo microscopes group (IIRC, it's called David L).
As far as I know they are still there.

David

Check out this page.  The company makes adapters for various cameras
plus optics to replace conventional microscope eyepieces.

http://scopetronix.com/