A couple things as I've been doing shooting of coins recently that hasn't been discussed.
1 - looking at your photos, #1 is particular, you are shooting through plexiglass / plastic. This in itself is going to cause detail loss and maybe missed focus. You don't want any "clear" covering over the image subject. Also make sure you aren't using a cheap filter on the lens.
2 - in trying Macro/micro I've found that it requires me to get too close, which is preventing proper lighting. So my next tests may be getting a longer macro lens such as a 105mm so I don't have to be right up on the subject and blocking my lighting. Otherwise, you'll have to crop (chop it up) the image to make it larger.
At some point, as mentioned previously, you'll want to use a Tripod and a remote release.
On Tripod work, if your subject is hanging perfectly vertically then all is good.
I've gone towards taking photos from above with the subject on a flat surface. I've found having a tripod with a "swing" arm able to accommodate this setup helpful, though I have my tripod laying on a shelf so the camera points straight down. A flippy screen (such as on a Nikon d5x00 series bodies) becomes really helpful in this situation as does LiveView - I don't know if the D50 has liveview (see the focusing/image on the rear LCD before you shoot).
that's what I've learned 0.02 cents worth
