This is one of the oldest, and most affordable tricks, for close up photography: the reverse ring. With this $10 adapter that you screw into the filter threads on the front of your 50mm lens, you can turn it around and mount it to the camera face first. By doing so, you increase the magnification of the lens substantially.
We used this trick in the film days, but it was hard to predict results with it. Since the lens is reversed, you don't have autofocusing or auto exposure. But now, thanks to Live View on most DSLRs, you can see exactly what you get before pressing the shutter button.
Also keep in mind that with most of today's autofocus lenses, you don't have an aperture ring to control depth of field. So you're shooting wide open, often creating a bit of a "Lens Baby" look.
But since the lens is reversed, you can use any make or model glass that has the right filter thread diameter. So that old Pentax 50mm you have in the closet that does have an aperture ring, can now be pressed into service on your modern DSLR.
And like many of these types of techniques, an hour or two of experimentation can spur your creativity and lead to something really interesting.
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