Axial Lighting - Please help!

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Hi all,

So let me begin with this has been a long long struggle for me trying to achieve perfection, so I've come here to find out if that isn't actually possible after all. I'm talking months of waiting for equipment to arrive, hours and hours of fiddling with angles and lighting.

My aim is to produce a setup that enables me to photograph many 100s of coins, after a lot of experimenting with "normal" lighting I came across Axial or Front Directional lighting and though it could be the answer! I am unable to post links as this is my first post, but a simple google for "axial lighting photography" should give anyone who isn't aware the setup I'm referring to.

The issue I'm facing is what I call "ghosting", this is where (after a lot of head scratching! I've found that there is a duplicate image reflecting down from the back plan of the glass. This can be seen in the first image attached. I've used 2mm and 3mm glass, and the "ghost" image is offset a little further on the 3mm glass which tells me it's coming from the back plane.

I have purchase single sided AR coated glass and the result is actually worse, I have no idea why.

The second image attached shows a much fainter ghost, but it is still there. My main concern here is that i'm trying to produce the highest quality images I can for archival purposes, and this overlay even at say 5% opacity, will cause the whole image to have a slight blur over it.

I'm here really to find someone else who uses this technique and has come across the same problem, or if someone uses the technique without these issues to share their setup with me!

Thanks in advance.


 
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If the ghosting is being caused by light reaching the other side of the glass then the fastest solution is just to prevent that light from reaching it no? Stick something behind it that'll block the light being sent back.

Ultimately though wouldn't it be better to use a different lighting technique? You're always going to end up with lots of light reflected off the surface of those coins.
 
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John
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This problem may be caused by unwanted spectacular reflection off the glass surfaces. You could try using a circular polarizing filter to try and minimize the the effect. If this helps, you could go further and polarize the light source. You can get sheets of polarizing material from Amazon at very reasonable prices.

Photographing highly reflective objects has always been a challenge . Have you tried a ring flash? I'm not sure though it would give you the results you want. Another suggestions is to make a simple rig from white card. a small hole in the center so that the camera lens can poke through you the carefully illuminate the card , ensuring your lights do not shine into the camera lens. ( A lens hood helps .The only drawback is that the illuminated surface of the card is not complete ( due to the lens cutout) this however may not be noticeable if the photographed surface is not a mirrored surface
 
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Steven
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I'm 99% certain this is being caused by light from the camera side. I've seen similar ghosting due to light reflecting off of the sensor onto a lens element or lens filter, but because the thickness of the glass affects the displacement, it must be related to the glass pane being used to redirect the light.
Is there anything nearby behind the camera to reflect light back? If so, flag it. If you have a filter on the lens, try removing it. You could try a different lens that may have better AR coating, or you could try adding a high quality filter with AR coating. Using the thinnest pane of glass you can find will help, but it will also bounce less light. Or maybe angle the lens to relocate the reflection.

The only other thing I can think of is to switch to a white BG... if the BG is already blown out then adding a reflection there will not show up (just like it doesn't show in the BG behind the monkey in the first coin). This might be the easiest answer...

EDIT: I just re-read where you purchased single sided AR glass. Maybe flip it over? Or use it as a filter instead?
 
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Dominic
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Ok, I might be being a bit thick here, apologies if I am, but what is the glass for, is the coin laying on it?
 
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Steven
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Ok, I might be being a bit thick here, apologies if I am, but what is the glass for, is the coin laying on it?
No, the technique uses a plate of glass at 45* between the lens and object... it is used to reflect light (from the side) onto the subject and directly inline with the lens.
 
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David
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Try a Dome light or CDI (cloudy day illuminator), I work in machine vision and an axial light would not be my first choice for this application as surfaces that are dead square (parallel to the camera) will always be reflected back as bright areas, uneven surfaces will appear darker as light is projected away from the camera lens. A Dome light gives very diffused light from multiple directions so evens the coin intensity

I’m not in my office today, but have co-axial and dome lights, red LED versions only, but I could take some monochrome images tomorrow to show the effects, just let me know in this thread.
 
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as surfaces that are dead square (parallel to the camera) will always be reflected back as bright areas, uneven surfaces will appear darker as light is projected away from the camera lens
That's the point... maximum contrast/detail... and no reflection of the camera/lens.
 
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Dominic
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No, the technique uses a plate of glass at 45* between the lens and object... it is used to reflect light (from the side) onto the subject and directly inline with the lens.
Thanks for that, now I know :)
 
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