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Forum: Pentax K-r
02-21-2012, 04:26 PM
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A longer prime on the camera, a short prime reversed on it. You can get some pretty crazy magnification this way. For example, a 28mm reversed on a 135mm will get you almost to 5:1. Divide the shorter focal length by the longer one to figure out magnification, assuming both are focused to infinity. So, a 50mm reversed on the end of a 100mm would be 2:1 (nice round numbers to visualize).
Of course you can mix it up and try reversing zooms, or using a short prime reversed on a zoom lens. Behaviour of them gets less predictable that way though, with regards to working distance and such. Also keep in mind the effective aperture, using a slow zoom will cause some additional loss of light and might make focusing tricky.
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Forum: Pentax K-r
02-21-2012, 02:00 PM
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This is the one I got, works fine. You have two choices, either get one that matches the two lenses you want to use (so if one has a 49mm thread and the other a 52mm thread, you get a 49-52 reversing ring), or you can use step up/down rings to make it compatible. I do the latter, as I play around with a variety of lenses. The bit of extra extension from the step rings doesn't seem to interfere at all.
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Forum: Pentax K-r
02-20-2012, 07:13 PM
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Go for it. Just about any lens, even the really, really bad ones are worth $20, just for the experience.
If you're at all into macro, remember that some really junky lenses are really sharp when reversed... You can get a reversal ring or adapter (one lets you stick a reversed lens on another lens, the other directly to the camera mount) for $3-5 on Ebay.
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