Strange m42-OM adapter with corrective optics

[Alfonso B]

http://www.ebay.com/itm/Pentax-PU-t...854581?hash=item465e6c1df5:g:xcsAAOSw2xRYfaPn

I found this strange adapter on eBay. Seems like there's correction optics to increase flange focal distance of a M42 lens by about 10mm to allow infinity focus on OM bodies. Is the element a negative apocromatic doublet, like an opposite version of a close-up lens? Does it significantly affect focal length or image circle?

That lens group could be useful with infinity reach issues, experimenting with those ultra fast x-ray lenses..

 

[radi(c)al_cam]

http://www.ebay.com/itm/Pentax-PU-t...854581?hash=item465e6c1df5:g:xcsAAOSw2xRYfaPn

I found this strange adapter on eBay. Seems like there's correction optics to increase flange focal distance of a M42 lens by about 10mm to allow infinity focus on OM bodies. Is the element a negative apocromatic doublet, like an opposite version of a close-up lens? Does it significantly affect focal length or image circle?

That lens group could be useful with infinity reach issues, experimenting with those ultra fast x-ray lenses..

You're basically right, the trick is as follows: These adapters are usually some sort of 1.1–1.3x tele-converters. But given the USD 6.00 price and the obvious lack of a maker's name or brand, I wouldn't expect too much in this particular case 😉

 

[Alfonso B]

Thanks for your thoughts. While possibly not forged by elves, it could still be usable with x-ray lens applications as they usually have pretty small exit pupil diameters and could also benefit from increased image circle, at least on ff. But you coud no longer claim to have a magical 0.85 lens..