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02-08-2012, 01:00 AM   #16
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QuoteOriginally posted by Lowell Goudge Quote
I would tend to think you would to look at maintaining the element to focal plane / sensor geometry or distance of a Pentax system but the element to mount (for the lens mount ) of a canon system. Maybe you can make some minor adjustments by moving the TC group either forward or backward in the TC
seems you were right about moving the group of glass. I got a minolta teleconverter (only needed 2mm adjustment instead of 3.5mm like the canon). I was rather frustrated to find, that while the mount was just a flange that screwed to the lens like most lenses, the tube containing the glass was attached to the mount only again. unlike the other one where it could only be attached in one position, this group of glass threaded into the mount and used a lock ring. I threaded the group of glass forward quite a bit ( I think it came close to hitting the glass on the lens but not quite). The result was not only infinity focus, but WAY past infinity focus. That was with an unmodified minolta mount hand held to the pentax camera so it would have been macro only had the group not been screwed forward. I guess since the group threads to the mount, my only option would be to flat the mount, and attach a pk adapter over it. I suspect it would still work. Unfortunately the 1.5x kiron for the canon is not like this, and will have to be cut way back unless I can come up with another plan. I found out that my minolta body is a maxxum too (no good for playing with md lenses). No big deal on the camera as it was in a lot of 5 bodies for 15$, so no big loss.

Thanks for the suggestion. It might really help with some adapters if I ever get any finished.

02-22-2012, 08:19 AM   #17
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@Lowell Goudge, thanks again for the recomendation about moving the group. While it didn't help with the first one, it was just the trick for the second one.

Just in case anyone is interested, here is my progress. The first one (vivitar canon fd 2x) is complete and the mount is attached by epoxy. It is a loss at faster apertures at least (IQ is terrible). It could be the lens (acquired from an unknown source and may have had fungus removed, I don't remember). For canon I should have removed 3.5mm but wound up removing about 6mm trying to get infinity focus so that may have caused issues too. I now know it could be the converter was not well matched to shorter lenses. Mechanically it is a complete and working unit though with infinity focus.

The second one is showing promise. I do not have a fast minolta lens to test with and there is no daylight right now (dark, overcast) so no conformation of focus from the camera. The only minolta lens that has not already been converted to pentax had the aperture ring loose and no detente ball, so I'm trying to hand hold a heavy lens to the camera, hold the aperture ring turned to wide open, and focus all a the same time with not enough light. Despite it all, after taking several shots, the lens shows promise. the few close to proper shots seem to show no major issues including bad IQ, with an f3.8 lens anyway. I have an f3.5 minolta lens on the way (I would like something like a 50mm 2.0 to test with but I'm broke right now). It is complete except for attaching the m42 adapter to the lens. I have decided to try and find a better way than epoxy to attach it. I'm thinking along the lines of 2-56 screws but I'll have to find somewhere to order a tap and screw that doesn't cost a fortune.

Since I'm stuck on attaching the mount right now, I think I'll move on to another canon one (if I have one, if not, I have some on the way). I'm really hoping to find another with the glass threaded where its position can be moved. I'll test the minolta out more when I have better daylight.
02-22-2012, 08:40 AM   #18
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It seems I might have some good news too. It looks like the group of glass can be threaded as a unit in the canon fd kiron 1.5x. I won't know how far it can be threaded or if it will do me any good till I rip it apart and tear the baffle out (the baffle prevents it from threading more than a little bit).

I also just got the thought. The baffle is gone on the one that works poorly, and the epoxy is a bit shiny. I read on a bird photography forum about people adding baffles to some teleconverters to improve IQ. I wonder if the reflective surface of the epoxy is causing problems?

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