It's not only camera makers who are not shipping manuals with their products. My son got a Vizio TV, and it came with a skimpy Quick Start Guide. Inside, it said that in order to "reduce paper waste," he would have to go online and download the Owner's Manual.

I don't see an Owner's Manual as being a waste of paper. Maybe Vizio is trying to save money. Unless you have the manual on a laptop or tablet, it's not very convenient referring to the manual while working on the TV. Printing 50-something pages puts the expense and "waste" at the feet of the consumer.

Could you please post two pictures (check "store original" for both), of items taken with both cameras. Also please let us know how large the items are for scale. Thanks.

The Nikon system has several "macro" lenses for "super closeups", and other lenses for Nikon cameras have varying levels of closeup performance. The best number to look for is "maximum reproduction ratio", and for your 50mm f/1.8, it's 1:6.6. This means that an object 6.6 times the size of your camera's sensor will fill your picture. With the D5100, the sensor is about 24x16 mm, or approximately 1 x .6 inches. With the 50mm lens, an object 6x4 inches would fill the frame, so you could take a full picture of a 4x6 print. The subject would be 1.5 feet from the lens to take this picture.

One problem is that lenses rarely perform their best at their extremes, and this applies most to their maximum aperture and closest focus distance. So your lens will do better at f/4 than at f/1.8, and focusing at 3 feet than at 1.5 feet. That's why the it does great with the pictures of the grandkids. Macro lenses are designed to perform very near their best at their closest focus distance,

If you really want to get better pictures of your jewelry, you want a "macro" lens. There are a number of options available, depending on your budget. One thing to be cautious about: make sure you get an AF-S lens. There are some excellent older lenses available, both new and used, which are not AF-S lenses, and they are generally cheaper than their newer counterparts. The AF-S lens has it's own focusing motor, which other AF lenses generally do not. They autofocus using the focusing motor in the camera, but your camera doesn't have one. There are many who say they manually focus their macro shots, but I think you at least want the option to autofocus.

To help you further, you could give us some more information:
* Post examples of the jewelry shots from both cameras (again, please use "store original" with each picture).
* Which other lenses do you have for your Nikon?
* Would you consider a macro lens, and if so, what would your budget be? Here is the search result for options at B&H.

http://www.bhphotovideo.com/c/search?ipp=100&atclk=Brand_Nikon&ci=274&Ns=p_PRICE_2%7c0&N=4288584247+4108103566+4109120021

Teddy - this discussion has moved beyond your original question. I'm in the consensus that you'll be happy with the D7100. But, I remain concerned about the need to purchase new lenses and / or sell off Canon related equipment you still have, if any. I'd add an additional caveat regarding the advancement in complexity of the D7100 model vs the Rebel line. I was a bit put off by the learning curve in making the change from a Rebel XTi to a 7D. You'll also have to learn a new camera menu and physical layout where the same controls are not in the same places ...

Regarding the Nikon vs Canon debate this post has renewed, let's look a bit deeper into two details brought up in the discussion so far: pros on the NFL sidelines all have white lenses and Canon gave up on their legacy owners (the FD mount vs EF). I can't find where I was reading about the Canon decision made in late 80s, but the analysis was that Canon made the right decision to move to a system that supports all electronic auto focus as compared to the horse n buggy era of the manual focus FD lenses. I had a camera from that era with two FD lenses that left me on an island of forgotten technology. I didn't embrace digital and fell out of photography as film went out of vogue. The person analyzing this decision said it was Nikon that missed the boat as they didn't think professionals wanted auto focus. So when we look at MNF today and see all those Canons, it can be traced back to the decision to introduce the EF mount and the subsequent line of EF lenses. Canon locked them into the EOS / EF system and kept them there via continuous updates and improvements that made it cost prohibitive to start from scratch with Nikon. Which is one of the underlying issues unstated in the OP's question ...

That same analysis (I'll find it if I can) also pointed to the alphabet soup of Nikon lenses and bodies. The legacy Nikon lenses may mount to all bodies, but will they auto focus? I know it's not that complicated, but to the uninitiated without a decoder ring, it's a guessing game about which Nikon lens works with which Nikon body. There's none of that confusion in the EOS / EF system. Every EF lens, regardless of age, year released or whether it's been discontinued, that lens will work on every EOS body.

There's always going to be a new and better body. But, are you in a system with long-term viability? Of course in Nikon and Canon you are. For the other brands of interchangeable equipment, are those other companies big enough / dedicated enough to continue to fight it out over just a sliver of the overall market share?

(And thanks Baltimore, we needed that L up in Detroit ...)