Why 90mm+ Lenses For Coin Photos, And Not 40-50mm Lenses?

If you dont get a proper copystand where you can make minute adjustment, you might get away with suboptimal adjustement on the frame by cropping, assuming your camera has a >24MP, it all depend what you want those pictures for ; is it for your own enjoyment, zooming to see full details on your computer screen or is it just for selling?

If you do this purely for coin photography, id put more money on a copystand than on the camera itself

Here's the kind of details on a small 1 cent you can get with a 24MP APS-C sensor (Nikon D5600 who can be bought for USD$250 on the second-hand market) considerably lowered quality so they can be published here.

Those pictures are beautiful. Although the little worm crawling into the king's eye is creepy.

A $300 copy stand is not in the current budget. Maybe someday. I am also a believer in approaching expensive learning curves slowly. I don't want to blow my budget on equipment before I really understand how to use that equipment correctly.

It doesn't fill much of the frame, but when I zoom in, the tiny details on the coin are still quite clear. That's even after the forum software has reduced the file size below 300kB. An American dime is almost twice the diameter of your example coin. Can I ask what camera body you are using with the 105mm lens, and the camera resolution? It must be pretty high if it can represent the coin that well in 10% of the full frame.