Photography question

[Roerbakmix]

I have two questions for the photography experts on this forum (e.g. @Kaleun96, @dougsmit, @kirispupis)

1) I have a Nikon d3200 DSLR, and have recently bought a nikon 60 mm F2.8 auto focus lens, which I also use for portrait photography (nothing too fancy: monthly photo's of my kids. This was of course the argument to persuade my significant other that I needed this lens, but in reality, I wanted to use it for coin photography...). The problem is the working distance: only about 10 cm. In hindsight, I should've bought a 105 mm. So the question is: are there any (cheap) tricks to increase the working distance? 

2) I use a poor mans DIY setup (with a different, manual focus lens) for axial lighting and black background which works OK, but it's really difficult to get it right each time. I'm considering a totally different approach, much like the ROMA photo's with the grey background, and also similar to the photos of @kapphnwn. Two questions: what material is used by ROMA? Is it just grey paper, or something more special? Second question: would this type of photo allow me to remove the background in e.g. photoshop easily? 

Hope I've worded my questions clearly enough; I've got COVID since a few days and am feeling a bit foggy.  

[Kaleun96]

1) Good question, I haven't come across someone trying to do this before and the only thing that pops into my mind is decreasing magnification. So for a prime lens like your 60mm, that would mean focussing on the coin from further away with the trade-off being that the coin now takes up less of the image. If you've only just bought the lens, you might be able to return it for a 90mm to 105mm macro. Basically the only thing within your control for increasing working distance is increasing the minimum focus distance as you can't reduce the length of the lens nor the flange focal distance. So basically you'd need to change the focal length of the lens and I'm not sure if there's an easy way of doing that without reducing the magnification, increasing the magnification, or altering the optical performance.

2) I think Roma replaces the background for these photos as the coins always seem to be centered perfectly in the same spot and the drop shadows are very similar. They do a very good job of it. In general, a grey background like the one they use will make life difficult for removing later if shooting silver coins, or even some bronze and billon, on the background directly. You want the most contrast between coin and background so the first thing you want to do is raise the coin off of the background otherwise it will cast harsh shadows around the coin and not result in a clear separation between the coin and background. A pure white background is generally best for this, though you have to be careful it doesn't reflect too much light on the edge of the coin or it will "bleed" into the coin's edge and make separation difficult.

I did some experiments with this here, though I forgot to post my final prototype (but you can find it here), which I have been using now for a few months with good results. In the end I just had a big LED COB separated from the coin by a sufficient distance, a diffuser, and some aperture control to help limit the light from bleeding into the coin's edge. You want the light to emit perpendicularly from the COB, rather than spread out and bounce off every surface. A bit complicated for most so I'm not suggesting you try to replicate it, rather just keep the same principles in mind. Shooting with lots of natural light will probably help expose both the coin and background quite well while also reducing shadows.

Though I should also add I was going for near pixel-perfect results with my background removal. For most, and likely including Roma, such results are overkill and you can get by with more imperfection in the coin-background separation. So just try to remember these few principles and you'll probably be OK:

• Contrast between coin and background. The more contrast the better. Not every background colour will work for every coin but white is generally the most universal in my experience. The key to high contrast with a white background is making sure it's exposed correctly, often if you just expose for the coin the background will be under-exposed and thus darker/more grey.
• Control reflections. You don't want any light illuminating the edges too strongly. Often this happens when light bounces off the white background, then bounces off something else nearby, and the hits the coin edge, producing bright spots on the edge.
• Separate the coin from the background. Raise it off of the background to help create separation between the in-focus coin and out-of-focus background. This also helps reducing the shadows from the coin blending the separation between the edge of the coin and the background. The downside with more distance between coin and background is that the background will likely be getting less light, and thus under-exposed, so you may need to illuminate it separately from the coin.

 

[dougsmit]

Since you asked for the cheap answer:  Unless you are making large prints, modern DSLR and mirrorless cameras have a lot of resolution to spare so you can just shoot from farther back and crop the result to get what you want.   My latest camera has 32.5 megapixels and responds well to cropping.  I am not familiar with Nikon models.  

If you want a consistent gray background, replacing is easier than shooting that way.  It helps to have some light reflected onto the edges before starting and there are software routines sold that do cut outs but I only shoot black backgrounds and have very little experience with cut and paste.  Every time I try white or any other color, I say 'why?' and go back to the black I prefer.  I have insufficient interest in the subject to try to figure out how to take every kind of coin photo so I am not good for such questions.  I don't patronize Roma, shoot Nikon or like gray.  Sorry.

I made this slideshow for a local (non-ancient) club 15 year ago.  In it I mentioned replacing backgrounds but have done nothing since. 

https://pbase.com/dougsmit/coinphotobasic