I did something similar back when I first go my camera. I could see the camera switch the plane of focus from the coin's surface to the slab's surface. Not a viable solution. Yes it does (I just looked in the manual). I've never used it. I'll give it a try.
I used the Live View technique and it appears to work well. I find it a bit touchy so I'm going to change my f-stop in order to gain some depth of field. And also adjust the ISO to accommodate the slower shutter speed when I do that. I hope that will make the process easier to deal with.
I find the LV works very well for me. I set the camera on a tri-pod, engage the timer mode, aperture priority (5.6), ISO (64). Exposure time 1/40s........
Two Verilux goose-neck lamps at 10 & 2 o'clock.......white balance set at florescent (daylight......6500K).
Oh, one more thing.......can you close your view finder on your camera Kanga? I always close mine when I do a photo in LV.
If I understand correctly, using LV automatically lifts the mirror used by the view finder, i.e., essentially it's taken out of the process.
Right, but you also want to eliminate any light getting in through the viewfinder and throwing off (maybe) your exposure.
Is it possible with your setup to tether your camera to your computer, and control it from there? That's what I do, and I find it vastly easier than trying to look through a viewfinder or small screen.
I thought I remember you getting a Canon a few months ago. The T3i is a great camera. The tethering software that comes with it is worth its weight in gold. I think for the Nikon D90 the tethering software will have to be purchased separately. It's a shame that a company as large and successful as Nikon can't include this software with the camera. Focusing will never be a problem again for those of us with less than 20/20 vision.
I've got a D810 (Nikon) and the camera can connect to the computer, but only for the purpose of transferring photos.......
There is wireless tethering available for your camera, although it's a little expensive at around $300. https://www.tethertools.com/product/camranger-wireless-tethering-system/ Here is a link to a database of assorted tethering software solutions. https://www.tethertools.com/tethering-software/
You should get a white balance card and use that to white balance the camera (or a white sheet of paper). Just white balance it with the same lighting you'll be using for the photos. It will make a world of difference.