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How to photograph small crystals "chatons" without having any kind of reflections ? Answered

I'm trying to inspect the deformation of small crystal chatons by image inspection, and I'm trying hard to minimize the reflections of light done by the geometrical shape of the crystal.
I tried so many different ways and techniques, and i was wondering does the IR imaging do any help for this problem..?!



Best Answer 7 years ago

You gotta really think about what you're asking: Objects that are transparent, with polished surfaces can only be photographed in two ways--via diffraction (light bending as it passes through) or via the reflections off the polished surface, so-called "specular" reflections.

Diffraction effects also include internal reflection ("total internal reflection", etc.)

For many transparent objects (glassware, etc.), both techniques are used together--some light passing through, and a diffused light source for defining the surface.

Diffused lighting will show imperfections in the surface, but will that show the "deformations" you're looking for? I don't know--not enough information. Can the deformations be detected from the surface alone?

Also, these Chalons seem to have an opaque reflective backing, too. So you cannot use diffraction from behind.

A light source for diffraction is usually large and diffuse (and behind the object)-- or it could be a "point source" light. Such a point source could be used from the front to capture diffusion but only by bouncing off the opaque reflective backing... So point-source will probably only produce a bright spot--or several, depending on the internal reflections of the facets. Would that be useful?

One more point--this is technical photography, not artistic. If you want to compare each Chalon to a "benchmark" standard, then it's much easier if the orientation of each one is identical. I.E., each of the seven chalons in one photo will have different angles to lighting and camera, making them harder to compare... Orientation makes a BIG difference with specular reflections.

(A resume isn't an argument, but I have a BFPA in photo-illustration... ;-)

Can the deformations be detected from the surface alone?
-- yes, deformation of shape could be spotted form the front face of the crystal.

your totally right, chatons are covered with a mixed chemical liquid of silver,gold, and some other metals and solvents.
I'm trying to detect and calculate the shapes of polygons and triangles in the picture of the crystal, thats done by detecting shapes and edges in the picture.

yes this is technical photography, not artistic.

I have a potential solution but sharing it depends on your specific end-purpose (ie, scientific, advertising, mfg inspection, etc.) . Can you elaborate on what you're doing that requires characterization of deformations in the chatons? Are you located here in the US?

this is a scientific research in machine vision inspection.
I'm not located in the US.

thanks for the reply.

I see from another reply you made that what I was thinking of would not be suitable for your purpose. I thought you were looking for internal structural deformations rather than facet information.


7 years ago

Im tempted to try a pre-polarized sodium light beam through a coherent
small dia. light pipe illuminating a single facet,  then focus much much
closer to my subject.


Didn't try it before, I'll look for a one i can borrow any try it.


7 years ago

Use a polarizing filter. They are specifically designed to remove glare and reflection from water and glass and such. Even leaves will have reflections so these filters are made just like sunglasses to remove reflection and let only the rich colors through. I use them all the time and they are essential to good outdoor pictures.

Try a very diffuse light source ?

That would be my thought -- a "light tent" or something similar.

I don't think IR buys you anything in terms of reflection control.

You may have to make two or more exposures moving only the light source.