[meteorite-list] Circular polarizers and micrographs

From: STARSANDSCOPES at aol.com <STARSANDSCOPES_at_meteoritecentral.com>
Date: Sun, 7 Jun 2009 17:40:21 EDT
Message-ID: <bb9.45830f18.375d8dc5_at_aol.com>

Hi List, Many of you are not at all interested in meteorite micrographs
but quite a few list members have contacted me over the years about various
aspects of meteorite micrographs. Many list members are taking very high
quality shots but have not shared them with the list yet.

In my Meteorite Micrograph Gallery I primarily use three different
microscopes. One of those scopes happened to be set up with a circular polarizer
in the analyzer position. This setup worked well with my Nikon auto focus
camera but I found I had better results with an older camera on my other
scopes.

I set out to figure it all out. Many of you are way ahead of me on this
one but this could save a lot of trial and error for those who have not
given it much thought yet.

This is copied from an advertising site for Hoya filters.
http://www.thkphoto.com/products/hoya/gf-04.html

"Light rays which are reflected by any surface become polarised and
polarising filters are used to select which light rays enter your camara lens. PL
(Linear Polarising) and PL-CIR (Circular Polarising) filters have the same
effect, but it is important that you choose the correct version for your
camera. They allow you to remove unwanted reflections from non-metallic
surfaces such as water, glass etc. They also enable colors to become more
saturated and appear clearer, with better contrast. This effect is often used to
increase the contrast and saturation in blue skies and white clouds.
HOYA's polarising filters do not affect the overall color balance of a shot."

While we are not interested in white fluffy clouds, we are interested in
clear sharp focus and linear polarizers detrimentally affect the focus when
used with auto focus cameras. They can still work but you might need to
take several shots to get one good one.

I have found that you can use any polarizer in the first position (based
on the light path) but the final filter (called the analyzer) is best if it
is a circular polarizer. The auto focus is better and also fast and crisp
so your camera doesn't sound like it is sawing logs trying to find focus.

I just set up all my scopes with circular polarizers in the analyzer
position. This was no easy task as none of the old aus Jena gear had a circular
polarizer option (They were made prior to many auto focus cameras). I had
to take larger sizes of filters to my rock saw and shape them into the
correct size by holding them against the side of the blade and rotating them.

If you attempt a change out you will like the results. You will also
notice the circular polarizers are directional. That is they only work
properly in one direction and not the other. And yes, camera filters are just as
good as original equipment polarizers.

I have a couple shots I would like to share as an example. They were
taken with an auto focus Nikon, through the eyepiece using a circular polaryser
analyzer. I will send them full size to any one who is interested.

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Received on Sun 07 Jun 2009 05:40:21 PM PDT