Caution Mounting mistake!

Under 48 customer reviews yet had only a negative (1 star): "unstable intermediate rings" from 25.6.2010.
I did something similar found, but only one of the 3 rings (the ring 20 mm): The camera-side bayonet was screwed not stable, so that the attached lens including intermediate ring clearly hanging down. The reason was as follows: There are 3 screws securing the metal camera-side bayonet ring. However, the above preferred screw must be approximately 2 mm shorter than the lower two screws, as the top hole is less deep. In one of the 3 intermediate rings a long screw was up accidentally been used, for which the hole is not deep enough, so that the screw head the bayonet ring not properly holds. Thus, the ring under load relented about 1-2mm. The thing was easy to fix: screw out, 2mm sawed down and back inside: now holds bombproof, the third intermediate ring, just like the other two!

So after this little rectification (1 star deduction), the product should have been still deserves 5 stars. All automatic functions are wearing. Both types of autofocus (the lens & the camera) function principle. Automatic Blendenuebertragung. Objective data to be moved over as if no extension tubes were used. The rings are very sturdy and the mechanism for locking and unlocking goes perfectly. The rings are a product of Meike from China, and they are absolutely worth their money.

For practical use: with the AF-S Micro Nikkor 105mm (31cm minimum focusing distance) to the D7000 (DX format) I can get a picture of 22mm image width bildfuellend without intermediate rings; with all 3 intermediate rings at the same time I'll come on 12mm image width at the minimum focusing distance (object for about 11cm in front of the front lens).
You can use the rings also to reduce the minimum focus distance of strong Teles. A numerical example (not too useful with my lens): with the AF VR Nikkor 80-400mm (minimum focusing distance 2.3m; at 400mm: image width 112mm in DX format) happens with all 3 intermediate rings at 400mm the following: by the greater distance of the lens from sensor, the focal length will become longer effective from 400mm to 560mm (ie as in the 1.4x converter), so I have now at 2.3m distance an image width of 80mm. Moreover, I can now but sharply up to 1.65m Distance filters (resulting image width 52mm). Note, now, of course, that I in it only can focus from about 4m and 1.65m back and forth with all 3 rings.
For wide-angle lenses are the intermediate rings quickly too thick: the thinnest 12mm ring alone is in a lens with 13mm focal length at infinity focus, the focal point exactly on the front lens. So you can get maximum even the dust on the lens sharp. At 28mm the other hand one could already do something (5cm in front of the front lens).