Lots Of Gear Don't Know How To Use It

I'll throw some ideas at you, don't hesitate to ask for clarification.

The best lens you have is that 50/1.8. That's the lens you want to be using those extenders with. I'll take a bad Prime over an excellent Zoom when creating a macro rig, ten times out of ten. Use the 1x only while learning.

Stick the D7100 on a tripod pointed straight down. You can use the corner of a table, or weight one end of a 10" wide board and stick the other end off the table to hold the coin. Drop a pocket mirror on the spot where the coin sits, and compose a shot such that the lens is centered in the image, looking at itself. That makes you square and parallel to the coin.

Aperture Priority, leave it at f/8. Use ISO if needed - you should be good to at least ISO800 - to keep your exposures above 1/100, but there's no need to be faster than 1/250. You probably have too much light if anything but blinding silver wants 1/400, and are getting highlights blown out. Use Exposure Compensation to fine tune. 2-second delay, of course. Don't be afraid to use more extension to reach 1:1 on the sensor, that 50 is a sharper lens than you think.

You'll find direct light better for luster and diffusion better for detail (trading each other off) but this rig ought to be good enough to use rather subtle diffusion - a couple tissue thicknesses or equivalent - to achieve a nice balance.

As long as those extenders work with the 50, you should be in good shape with the equipment on-hand. Of course, you can throw more money in down the road but what you have will get the job done nicely. If the extenders don't work, and I'm unsure they will, spend a few bucks on a reversing ring for the 50 and all of the above still applies.

First off THANK YOU. That was excellent. I do have a set of step up rings I forgot to mention so I can put the macro lenses on the 50 I think. Lighting is a challenge. Tonight instead of waiting for an appropriate response, I bought a ikea clamp on led light to help( when your new to a hobby the excitement level is high). How to use tissue paper without starting a fire? Build a small frame? The speedlight has a built in diffuser I could rip it out but that might get me in hot water, plus it's small. I think the local menards has sheets of opaque plexiglass that could work. Someone also mentioned a styrofoam cup with the bottom cut out in another post here.
My coins alas are large and small, I got a few double eagles. Mostly halves, quarters and dimes. Have not started a penny collection though. mostly inherited, but I've been ripping up ebay for a month.

Use the 50 forwards if you wish for large coins, and reversed with a ring for magnification. Cheap extension tubes are another possibility, although those get expensive when you buy the ones that transmit lens data to the camera - the cheap ones don't do that.

Alone, the 50 will probably do 50% magnification (you won't be able to focus is the lens is closer than that) - a 38mm coin would be 19mm on the sensor. Your sensor on the D7100 is 15.6mm, so at 50% it will hold less than a full 38mm coin. 42% magnification makes a Morgan fill the sensor.

And your image size on a 24MP sensor is 6000x4000. That Morgan you just shot is 4x too large to see all at once on your monitor! And we haven't even started using Macro lenses yet.

For the moment while you're learning the procedure, just use the 50 as you would normally. No added mag lens. Get comfortable with setup, white balance, minimum focusing distance and the shot parameters that work best with your specific equipment. Learn to shoot coins. Then we'll worry about manipulating magnification, because added magnification reduces the size of the "sweet spot" for settings.

I just realized this topic is Don't know HOWLto use it. My bad.
Anyway here is a photo with the D90 (the Mrs. wouldn't give up the D7100. I think things turned out ok. Tell me what you think. My rig is kinda cool, I'll take a photo and show you.

Here is the setup. a Nikon d90 with a 50 mm f1.8 dx refurb lens. I paid $99.00 for the lens 4 yrs ago and it was never used. a cheapo $20 copy stand that wont fit a DSLR. A focus rail from ebay to allow a DSLR to fit. a jury rigged hot shoe extension to stabilize the vertical arm. one Ikea light, and a cheapo hot shoe flexible light that doesn't connect electrically to the camera.

Ha! I love it. I may not be reading this right since I'm on my phone, but it looks like the vertical arm has enough downward travel - and the camera enough upward - so it could become a load-bearing element. That would stiffen things, and frankly you're now working in a realm where little gains like that are important.

So how large are your originals? Are you autofocusing?

I'm thinking the focus rail can slide downward so the bottom actually touches the table and holds weight.

Custom white balance is a capability of all dSLR's. I don't know the specific steps for your camera, but it will involve setting white or gray paper (they make a bespoke 18% gray shaded card for the purpose) where the coin will be, with the lighting set as for the shot. You take a picture of the card and (via some setting) tell the camera that is "baseline." It is then able to correct color in-camera.

The tiny light position adjustments you make for each individual coin won't matter for this, as long as you're close to their final position to begin with.

My Canon is perfectly happy doing this with white printer paper. I don't know about your Nikon, but Ray (rmpsrpms) knows Nikons and will hopefully poke his nose in.

1) Always use the camera's maximum image size and quality. You're going to depend on postprocessing software to downsize the image later. In fact, if you want to go that far eventually, we'll teach you to use RAW files in your shooting. They're raw photographic data straight from the sensor, with no in-camera processing at all.

The reason for this is that cameras are very weak computers. It's preferable to do as much processing as possible on your much more capable desktop computer. Your goal is to do all processing at your computer, and directly upload a completed file.

2) Use only monochromatic shades for background. Preferably black or gray to minimize light reflected back into the lens. Reflected light is a problem in macro photography, moreso than other specialties. Work hard to minimize external light and surfaces that can reflect light back into the lens. Reflected light costs you contrast, and you are going to be adding a little contrast in most postprocessing operations anyway.

There isn't enough wrong with that Quarter image for me to offer any critique here. You're well ahead of the power curve in terms of quality - you seem to have the feel for how the coin needs to look which is a big help. That's teachable but difficult.

Find a well-worn and darker Lincoln - or something similar in your collection - and see what differences it requires for lighting and exposure.

so I tried the WB reading a out of focus white card, but had trouble. So I just took a series of photos with different K numbers with silver coins and pennies. I went with what I thought was the best 3450K. Here is an example