One niggle: I twitch about the words "spherical aberration" as used here. Ah, I admit I didn't bother investigating the term further and just borrowed it from your post from a decade (!) ago but now, after reading the other (quite helpful) thread you linked, I see I misinterpreted you as saying bot...

Well it's that time of the year again when I decide to revisit axial lighting for no good reason. I've been trying some various setups the past few weeks, partly influenced by this thread that I forgot to follow up on earlier in 2022. Reading through it again, as well as some of the old threads Rik ...

Just an update on this for anyone interested. The fresnel lens approach worked pretty well but I ended up going in a different direction for two reasons: 1. I was still getting this weird fringing around the edge of the coin in the final stack, similar to what the mirror produced, probably partly re...

Here's a close-up of the thread profile from the center of Image 1 (right), not too shabby if I just needed to measure the thread dimensions or characteristics of the thread if I had machined or printed it myself.

I printed a new platform with a larger aperture of 37mm and made a few other small improvements to it. I also printed a "shroud" for the fresnel lens, which doesn't do much except cover it up so light doesn't escape externally and reflect of things and also to align it with the rotation stage and al...

Had another quick play-around today. The iterative process of trying different setups is taking awhile as some things aren't practical to test without printing new parts. I made a new coin platform with a few holes in it to accept some of the lenses I bought. The fresnel lenses seemed to be the most...

The acrylic pedestal acts like a height extension pedestal, but without the fear of the coin falling off. I suppose it would be better for edge reflections if the outer cylinder of the pedestal was rough sanded and painted black to limit reflections back toward the coin edge. I was more curious abo...

There is an excellent and surprisingly high-end You Tube video that shows how to do this calibration. Unfortunately I looked but could not find it. I'll look again but you might try searching as well for axial lighting in coin photography with backlight. I'm terrible at finding such things so I'll ...

I'll see if I can do some testing this weekend and try rule out some other factors. I think if I can leverage the hole inside the rotation stage and place an LED at the bottom of it, I can effectively gain more height between the background and subject, though not as straight-forward as that if I th...

The usual method for doing white backgrounds with coins is to use a white backlit panel. I understand that you tried this but it resulted in undesired reflection off the coin edge, presumably due to placing the coin directly onto the illuminated surface. You could eliminate this problem by setting ...

You will need but a single gobo ring if you make it so that you can reposition it: shade.png Interesting idea, though I mentioned a bit earlier that I had tried a variable "mask" for the background using an 3D printed iris, the issue that prevented me from continuing with that is that the coins I p...

I have been shooting plants against white backgrounds for a few years intensively. In my experience it is far easier to get good results if the background is lighted and not a light itself. Use independent light sources for foreground and bg, one a flash unit, the other continuous light. I prefer c...

I've placed an order for some various Fresnel lenses from this European store: https://optomarket.net/ It seemed quite affordable, four lenses of 50mm in diameter and one holder for about 22 euro + shipping. Definitely in the price range that demands some messing about with, regardless of whether th...

Found some more Fresnel lenses that could be promising. I'm not familiar with data sheets for them so apologies if I get anything wrong. I've found a European supplier of the models in this datasheet (e.g. PL117440): https://download.khatod.com/documents/pl117440-test-report4930576.pdf They're all 5...

Yeah some really great ideas already! I can give blekenbleu's suggestion a go first, though I can't use a lens hood as I have my custom ring flash attached to it and there's only so much I can raise the coin off of the platform before it becomes a bit impractical and the greater the height, the more...