Ultrasonic baths and coins are a bad combination under most circumstances. I could see using one to get dirt off of ancients, but for modern coins, you have to be very careful that you don't actually damage the coin. Also, your lighting problem is either a camera problem or your lights are way too yellow. It's all about the Color Rendering Index (CRI) when it comes to lighting. I believe the Jansjo LEDs have a decently high CRI.
My light fixture was very low because my camera was low down as well. I saw the 10 and 2 o'clock positions in the article and I was there but my height wasn't correct with the light to highlight the coin correctly . It am honored to be complimented by both you guys as this is a totally new thing to me.
I'm just curious.. why did you use an exclamation mark in your date instead of a numeral 1? !894 ????
Like me, quite often, the Shift key got in the way of effective typing. Images this good with very small-sensor cameras like your Nikon indicate some really effective software implementation on the manufacturer's part - in-camera processing to create an image as close to reality as possible despite the small sensor which by definition will be "noisy." It may be that you can back off physically a bit, zoom in a little more, and buy yourself more room to light that way. You'll want to experiment with it a bit to that end. Zooming in increases the minimum focusing distance, though, so before you tweak lighting much you'll have to see how close you can physically come to the coin for a given zoom. And zoom lenses being a compromise, you may lose quality with a closer zoom as well.
I zoomed in as close as I could get before it became blurry. I have it set up on a rig similar to yours mounted on a very short tripod. This light fixture I have is also kind of wide just under par 30 size. This was my first attempt at it and I am going to experiment until I got it down. I also have 2 full size DSLR'S which I really don't think I need. I would rather use this one for this purpose.