Edit 4/7/2015 - I still stand behind that this product is better than many of the reviews listed here state, in that these are capable of really nice macro shots, but as I've used them more with other lenses, I have to subtract one star due to how poorly they hold heavier lenses. With a 50mm f/1.8 lens, they stay attached pretty easily, but if you try with a heavier lens, they barely stay attached to the camera. You should not use these with a heavy lens without the lens being constantly supported. No matter how tight I try to make the connection, it separates very easily from the lens. The locking pin doesnt seem to do much.
Otherwise, for the price, if you need a quick fix for a macro shot, or just want to play around with macro before investing large sums of money in a real solution, this is worth it. Just be very careful to not allow your lens to fall off your camera!
Edit 7/19/2014 - I uploaded 4 sample photos I took today using this exact product taken handheld with a Nikon D7000 with a 1978 50mm f/1.8 lens connected to the Fotodiox Nikon Macro Extension 14mm Tube.
I see a lot of negative comments for this product by people who clearly either had the wrong expectations for this, or simply don't know how to use it.
This is a lens extender which allows you to take any lens you have and turn it into a Macro lens (Nikon calls it 'Micro' but its the same thing). Essentially you can get a LOT closer to your subject and take some really extreme closeups. Although this technically will work with any Nikon SLR, and with any lens, you will get much better results if you use it with a "non G" lens.
When a Nikon lens has a "G" in the model name, it means it does not have a manual aperture ring. This means that the aperture of the lens must be set electronically by the camera. This extender does not pass the electronic information from the lens back to the camera, so in essence, your camera does not have any control over the lens whatsoever. That means that neither autofocus or automatic aperture adjustment will work, you must do it manually.
All Nikon lenses have a manual focus ring, but only 'non-G' lenses have a manual aperture ring. Most DSLRs sold today come with G lenses, meaning that if you use them with this extender, the lens will be fixed at its narrowest aperture, which is usually f/22. While this will work, you will get extremely dark pictures, so in order to compensate for it, you'll need to leave the shutter open longer, which increases the chance of blurry pictures without a tripod. If you ever hope to use this extender and shoot hand-held pictures, you really need to find a non-G lens.
The good news is that used non-G lenses are super cheap online. A really good one is Nikon's 50mm f/1.8 lens. This lens is available in D and non-D variants, both will work. The important thing is to make sure it does not have a G in the model name. Search your favorite auction site or classifieds site and you can usually find these used for under $100. Nikon has made many different variants of this same lens over the years, so you can actually find ones from the late 70s or 80s which will work just as well.
There are many other lenses you could also use, some with zoom capabilities, and others with a longer focal range. They will all work as long as they have a manual aperture ring (non-G lenses).
So assuming you have a proper non-aperture lens, you can connect it to this extender and it should connect to your camera easily. Since the lens cannot communicate with your camera, the camera will assume that there is no lens attached, so the only way to use your camera is to either use it in Aperture Priority (A-Mode) or Full Manual (M-mode). Your camera will not work in any other mode.
Its also worth noting that you can use either a DX or FX camera. I own a Nikon D7000 which is a DX camera. I guess I should probably add that although this could work on a film camera, I wouldn't recommend it, since shooting with this ring involves a lot of trial and error to get nice pictures, so you'd waste a LOT of film trying.
This product is actually three different rings all connected together. I don't recommend using them all at the same time or even the 28mm ring, because although this will give you EXTREME close-ups, your depth of field will also be extremely small, plus you would need your subject to be literally less than an inch from your lens, which will introduce lighting problems. I've found that I get nice results with just the 7mm or just the 14mm ring. You can use them in any combination you want, but like I said, the more you use, the more extreme the magnification.
Now that you have your camera with the ring and your non-G lens attached to your camera, you have to decide whether you want to use Full Manual or Aperture Priority mode. I strongly recommend Aperture Priority mode as you can still benefit from the camera's internal auto-exposure detection. In order to do this, you need to go into your camera's Setup menu. On the Nikon D7000, the setting I need is called "Non-CPU Lens Data". I imagine its called the same or similar on other Nikon DSLRs.
Go in there and pick the first lens number if youve never used this feature before. For focal length, set the focal length to whatever the focal length is of the lens you plan to use. Nikon makes DX and FX DSLRs. The FX models are also called "full-frame" cameras and are more expensive. Since most (possibly even all, I'm not sure) non-G lenses are FX lenses, you need to make sure you set the correct focal length here. If you have an FX camera and an FX lens, then just input whatever the focal length of the lens is. If you have a DX camera (like my D7000) and you are using an FX lens, you need to adjust the focal length by 70%. So if you are using a 50mm lens (like I am), you need to actually input 35mm here. If you have a 105mm lens, you put in 74mm.
The next setting in here is "Maximum Aperture". You can play with different settings, but I recommend f/11. Whatever setting you choose here, you must also have the manual aperture ring on your lens set to the same thing. Getting these two numbers to be the same on the lens itself and in the camera setting is important if you want your exposures to be accurate.
Once you have entered your focal length and your maximum aperture, save your setting and get out of the menu.
Now, you are ready to shoot. A couple of more tips while shooting is that I recommend doing this in brightly lit areas. Shooting plants, insects, or flowers is easy to do in direct sunlight. I do not recommend trying to use a flash as chances are the camera itself will be in the way of the light.
Shoot a couple of test photos of whatever you're trying to shoot to make sure things look ok. Don't worry so much about the manual focus of your lens. You'll find that you have much greater control over focus by simply moving the entire camera to keep the image in focus.
Get used to contorting your body and moving the camera around to compose your shots and get them in focus. As I mentioned earlier, using this product involves a lot of trial and error, but once you get a little bit of experience using it, you can get some GREAT results!
So, in summary, I think this is a great product that allows you to shoot some great closeups with lenses you may already own. Even if you have to go online and find a used 50mm non-G lens, the combined price of that lens plus these extender rings is still FAR cheaper than buying a dedicated macro lens.
This extender is made entirely out of metal, is easy to use, inexpensive, and when used properly, works very well. I honestly can't think of any reason not to give it 5-stars, and for those who did, I truly believe they didn't understand what they were buying.