[meteorite-list] Circular polarizers and micrographs

[STARSANDSCOPES 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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