Re: Advice on Microscope

From: Richard Knoppow <dickburk@ix.netcom.com>
Subject: Re: Advice on Microscope
Date: Sat, 28 Feb 2004 18:33:16 -0800

> I don't think you can see the actual grains of normal
> film with a standard microscope let alone a low power stereo
> microscope.

Richard, I don't think any of those was intended to be
serious. Sandy's initial post was concerned about processed films
containing image forming grains. Of course, in such a preparation one
wouldn't expect to see tabular shaped crystals. Silver halide crystals
used for X-ray and high speed negative applications are at most a
couple of microns (and everything else smaller) in diameter and you
know the limit of optical microscope...

> You need a magnification on the order of 10,000
> X to see the actual grains and I think that may be low. Most
> of the published pictures of grains are made with an
> electron microscope. What you will see in the stereo
> microscope are the grain clumps one seens in a grain
> focuser.

I am not an microscope expert at all, but based on ones I've used,
real "stereo" microscopes are low magnification models typically used
for dissecting microscope (For dissecting small specimen by hand under
microscope. With a bit of practice, I could easily dissect out tiny
brain of fruit fly larvae and split it in half. This thing is about 30
microns. If you talk to people who research on fruit fly genetics,
they can look at adult flies under those microscopes and single out
virgin female flies almost instantly. This is harder than cutting
brain out.)

Binocular microscopes that go to higher mags have one objective lens
and two eyepieces. It's a lot easier to use this type than ones with
one eyepiece, but neither type would allow depth perception.

Coming back to 3D view, there is a technique to make shadowing in
electron microscopy. Micrographs taken with such technique are seen in
literature.

> These may be actual clumps or stochastic clumps due
> to chance alignment of grains at different depths of the
> emulsion.

After all, I don't know what exactly Sandy's aims are. If he wants to
visually examine something to do with image reproduction, much of
these discussions are irrelevant because enlargers won't give 3D
images of grains, and won't care if apparently large crystals (and
therefore grains) are due to Ostwald ripening, coalescence or multiple
grains at different depths.

--
Ryuji Suzuki
"Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)