It worked finally!!!! :D
Continuing the revered theory, here is an exciting experiment I did with my 300mm zoom lens and the 50mm attached reversed to it, I've been trying this for a long time but didn't get it right, until yesterday when I was bored and nothing to do, I thought to give it another try, I found that what I was missing is that the subject must be very close to the lens and almost touching it, and voila!... here it is magnified!! :))
that made me freaked out and I harried to my parents shouting: it worked, it worked!!... and started to jump from a place to another to try different things to see how they look like, Pa got excited, Ma didn't know what I'm talking about but was happy for me, and my brother called me crazy, LOL!!
Now, seriously, how to do it:
there are several ways to attached the two lenses, the zoom to the camera and the other one (what ever it is) reversed to the zoom, there are rings already available for this purpose, or you can make your own one with some extra lenses caps, cut and glue.
what I did is simply sticking the two lenses hoods together with a tape, then put it backwards to the zoom lens, and from the other side the 50mm lens (see the photos below), and I didn't need to cut or paste anything.
keep the camera very steady, because it will be very sensitive to any simple shake and the photo will become a little shaky, and instead of moving the camera, move the subject slowly until you see the details (except when the subject is alive!! LOL!), the self timer may help is this case.
as mentioned before in the previous method, don't forget to put some folded safe paper in the aperture opening of the reversed lens to keep it wide open.
now what I've experienced when trying all different focal lenghes, both in the zoom and the 50, when putting the zoom at the highest focal length (here 300mm) it will give you even more magnification, and also it will give you its full frame, while when keeping it at the smallest focal length (here 75mm), it will appear as a spotlight, and of course less magnification, the other lens is better to be at its highest focal length.
you won't really tell what's the best until you try every possibility.
it will be better if you have a zoom lens with not very big focal length (like 135 or 200), because you will still be able to see the whole subject and with the whole frame of the camera.
in this photo I capture a little diamonds (fake of course :P ), with focal length 300mm, below is the same jewellery with 75mm, you can see the difference.
hope that will help, and hope I didn't talk too much, LOL!!
See a lot more cool examples Here, where the last one is my eye :))
Here is a very good tutorial to do the whole thing :)