Monday, March 11, 2019

Cross Polarization in Extreme Photomicrography




Chalcotrichite
This sample is from Ray Mine, Pinal Co., Arizona.  The chemical formula is Cu2o.  It shares the same formula with Curprite.

The reason my pictures of minerals seem to come slowly is because they do.  I'm learning as I go.  The minerals with the formula Cu2O have been an extreme challeng for me.  Without any accomodations the images turn out with the highlights blown.  I've tried several things to keep them from looking like the one below.

Chalcotrichite with blown highlights
The one at the top of this page is about the best I've been able produce.   Here is how I do it.

I place all of my minerals in a FotoDiox Portable Studio, LED 440 to photograph them.  I have incorporated Cross Polarization in this way.

FotoDiox Set up
I have made two filters to mount in the studio between the light and the subject.  The top one is what I call a softbox filter made of white nylon mounted on a frame.  The one underneith is linear polarizing film mounted on a frame.  I add a circular polarizing filter on the lens as shown below.

Circular Polarizing Filter
I can then twist the circular polarizing filter to minimize the highlights.  I also underexpose at least 1 stop. Adobe Bridge has a setting which controls highlights and I minimize that.

Clar Led Light 24B 
The multiple polarizing filters cause a many stops loss of light so some times I add  the above ligyht before closing the lid to augment the light.  In the image at the top of this page I didn't add the Clar Light but I augmented the ISO to 800.


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