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bobh

Axial lighting

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What kind or quality of glass pane do you use for this? I am getting frustrated because of focussing issues which I THINK are due mostly to aberrations in the reflective glass I am using. It's just an A4 (approx. US-Letter) size glass pane from a very cheap picture frame...

 

I am sure there are better (more expensive) alternatives, but since I don't know much about optics I wouldn't know what to buy.

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That is what I am using. Once in a while I get a focusing problem, but another try and it passes. You could switch to manual focus. But, if you mean there is an aberation in the glass that screws up your focus, then you definitely need to get another piece of glass. Maybe another picture frame would have a better piece of glass. All the glass is doing is aligning light rays with the lens to create an effect. The glass should not create out of focus areas unless in has a really extreme aberation. I would guess that is possible, but I think you would be able to see it. I do have problems at times if I get a reflection on the glass and my autofocus centers on the reflection. I use a black curtain to prevent that.

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I use a high quality glass piece with a thickness of ~ 2mm and a very smooth surface.

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I use a high quality glass piece with a thickness of ~ 2mm and a very smooth surface.

Thanks ... who supplies material such as this? Photo supply stores, specialty optical supplies, or ordinary hardware stores?

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How about window glass? Should be pretty even thickness and good surface. Any easy to obtain.

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Bobh, did you find an acceptable piece of glass? I want to give Axial lighting a try. How do you support the glass?

 

Im using a Nikon D7000 on a tripod pointed down, with my coins sitting on a table next to the tripod.

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Bobh, did you find an acceptable piece of glass? I want to give Axial lighting a try. How do you support the glass?

 

Im using a Nikon D7000 on a tripod pointed down, with my coins sitting on a table next to the tripod.

Sorry I missed your post, Josh ... guess I should start following this forum again!

 

I didn't pursue the matter any further yet; just haven't had time to look for other glass plates, or do much in the way of coin photography at all, for that matter.

 

I support the glass by putting two stacks of books with a gap in between. The glass rests on the books at the left and right edges, and the coin is in the middle. You need to put something at the base of the glass to keep it from slipping, obviously ... taping it to the table is one way, or you can tape a pencil onto the table and rest the glass on that (i.e. on the table but up against the pencil).

 

I found that the trick is to keep everything black (black books, etc.) to avoid any spurious reflections. I had to drape some black material over the camera tripod because I was getting relections of that, too.

 

It's fun! :)

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Sounds like fun, Bobh!

 

Im thinking of making a fixture out of wood strips, and using some picture frame glass. Im trying different lenses, as well. Im using a Nikon D7000. I dont have a macro lens, but my 70-300mm telephoto is working with an extension tube for close focus. seems to work OK, but focus is a bit of trial and error. The tripod helps ALOT! good tip about the black. some black barbeque grill paint should do the trick.

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I've had good luck with microscope slides for axial lighting of cents. I take a small piece of rigid black foam and cut a 45-deg angle in it, then tape the slide to the foam. You need to make sure you put a non-reflective black surface behind the reflector to avoid having it re-reflect up to the sensor...Ray

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I've had good luck with microscope slides for axial lighting of cents. I take a small piece of rigid black foam and cut a 45-deg angle in it, then tape the slide to the foam. You need to make sure you put a non-reflective black surface behind the reflector to avoid having it re-reflect up to the sensor...Ray

 

What a good idea to use the foam support ... thanks! :art:

 

I've been looking around online for laboratory / microscope slildes, but most seem to be no wider than an inch or so. When I have some more time, I'll go to one of the laboratory supply stores here in Zurich to see if they have something a little wider. Some of my coins are 50mm in diameter (2 inches), and to get a good picture of those, you'd need a piece of glass that was at least twice that size in diameter -- and not too thick because that will have a negative influence on the image quality.

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