When taking a coin photo, it's essential to get a decent depth of
field, which means setting the aperture correctly. I find that f16 works best. The next question is how to deal with exposure time.
It's quite possible to let the camera calculate this. But care is needed. Left unadjusted, a camera will try to balance out the picture so that if colour tones were removed, it would
average a neutral grey. But what we want is for the coin to be correctly exposed, regardless of the state of the background, which is due to be edited out later anyway. Shiny highlights and dark areas can both fool the camera.
Here is a set of 5 shots of a
Sasanian drachm. (Ignore the other coin for the moment.) These are Photoshop thumbnails, and the exposure compensation ranges from one stop under to one stop over at half stop intervals. The best of these is half a stop overexposed.
That other coin is a small bronze of
Pergamon. The next image is a similar range of thumbnails of that coin, and you can see that in this case the best shot is half a stop
underexposed.
As a rule of thumb, this works for me. Bronzes, half a stop under; silvers, half a stop over; neutral tones, no adjustment.
More to come ...