Digital Microscope Or Stay With What I Have?

Try taking and posting a pic of an RPM with your current setup. Your pics seem fine as is. I have two scopes and try not to use unless I have to. I like using a point n shoot camera.If you do get a scope,get one that goes as low as possible and not higher than 150x.Also,you can buy a scope for under $20,so if you want to go ahead and experiment.The lighting will drive you
John1

If you are not tethering, are you at least using Live View? If not, you will never get a really sharp image from it at these higher magnifications. Tethering and viewing on-screen automatically forces Live View to be active, which in turn forces the vibration-free shutter EFSC function to be active. This eliminates both shutter shake and mirror slap. If you don't turn on Live View manually, then you will get both of these issues and sharpness suffers.

That said, I assume your ringlight is continuous? If it's a flash, then this helps to minimize both shutter shake and mirror slap if you have the flash trigger set properly.

Yes, I use live view, and I use the timer. The ringlight is not continuous, it also has an offset light (not just the ringlight) which is what I use. I don't use mirror lock up, but I haven't seen any camera shake, and I'm a pixel peeper.

Here is an RPM shot I just took. First is uncropped, second is a 100% crop of the RPM (it's a '56 D/D fyi). If I wasn't lazy, I'd do it again and focus more carefully.

The image looks to be suffering from "100% crop syndrome". This "syndrome" relates to the reduction of detail at pixel level due to Bayer demosaicing. Background is that the Bayer array does not give full RGB information to each pixel. The missing information must be interpolated, and this process results in reduced resolution.

Your camera also has an Anti-Aliasing filter, known colloquially as a "blur filter". This filter spreads information from each pixel to adjacent pixels in the array in order to minimize moire effects. Ironically, this actually helps to improve the Bayer demosaicing problem, but causes a reduction in resolution on its own.

The best way to reduce these effects, and ensure you are getting good final image sharpness, is to downsize the image by a minimum of 2x.

Problem is this will reduce your final image size as well, possibly farther than you'd like. To mitigate this effect, you can use a 2x teleconverter to "spread" the optical information across more pixels. There is very little optical loss in doing this as long as the teleconverter is decent quality. With the magnification effectively doubled, you can now downsize the image by 2x to eliminate the effect of "100% crop syndrome", and the final image will be the same size as the original (without teleconverter) but significantly sharper.

The nice thing about a 2x teleconverter is it simply magnifies the image 2x, while keeping the working distance and lens parameters fixed. You can get a similar effect with more extension, but if the lens is optimized at a lower magnification, its sharpness may suffer. This is especially true for dedicated macro lenses like the OP's 100mm Canon. It is not at all designed to operate correctly when extended an additional 100mm from the camera, and with the coin closer to the lens. This is well outside its design window. It is much happier just having a teleconverter take its 1:1 image and magnify it to 2:1. This is also true for duplication and reproduction lenses that are designed to operate in a narrow range of magnification. I learned this trick long ago using a 105mm Printing-Nikkor, which is happiest right at 1:1, and loses corner performance quickly at higher or lower magnifications. Operating it at 1:1, with a teleconverter, gave me a superb 2:1 image. More general use lenses such as enlarging lenses can be operated with extension at less loss of image quality. In fact, many enlarger lenses will prefer to operate at 2:1 vs 1:1 for instance.

An El-Cheapo Vivitar 2x-1 in M42 works very well for this purpose. They are typically <$20 on ebay. I prefer the newer ones (all black, no aperture ring) but the older ones should work fine as well.

Add-on "diopter" lenses like this one are a gamble. Most I've used don't work all that well.

EOS TC's are going to be more expensive since they generally transfer contacts to control the camera lens. Cheapest ones I see are in the $100 range.

Thanks Ray and Beefer...appreciate the info.