Tom Abrahamsson of RapidWinder.comIt is almost never that an inventor improves on a Leica product so that it is better than the original Leica product. Tom holds that distinction with his RapidWinder for Leica M rangefinders -- a bottom mounting baseplate trigger advance. In addition Tom manufacturers other Leica accessories such as his very popular Soft Release and MiniSoftRelease shutter releases. Tom is well known as one of the true Leica rangefinder experts, even by Leica.
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If you go to Flickr and use the tag "Orion 15 20mm f6.0" -thre are plenty of samples with the lens, both in Kiev mount and Ltm. It is a good lens, some rather significant fall off though - but no more than many other vintage wide angles. It is quite sharp - the Topogon design is still a quite respectable. Both Nikon and Canon used a similar design in here 25mm's - as did Zeiss with the originalTopogon 25. The Orion 15 is probably "throttled" down a bit from 25 to 28 - which would improve edge performance.
If you are looking for one, try to find a black anodized one - less 'sticky" focus helicoid. The chrome ones can "bind" a bit if not used regularly.
For some reason I have problem uploading to RFf at the moment. Don't know why - hence the reference to Flickr.