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10-11-2010, 11:24 AM   #1
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Old Minolta Rokkors on a Pentax?

My dad has some Minolta lenses from the 70's that I recently found that I am interested in using on my K100d. First here are the two lenses:
Minolta MC Tele Rokkor-QD 1:3.5 135mm Prime
Minolta MC Rokkor-PG 1:1.4 50mm Prime

I really like the 50mm, as it works fine if I just hold it up to my camera's lens port (is that what it's called? ) but needless to say that really isn't feasible for continued use. I love the feel of these lenses, and from what I understand through a few review I found, this is some pretty good glass from Minolta.

I believe they are very cheap now, I see the 135mm going for $80 on ebay, and the 50mm for around $40, so I'm not really interested in selling, I would rather use them myself.

I have looked and looked, but is there a way to convert these to the Pentax mount without shaving them down? They are still my dad's lenses so I don't want to ruin them if he ever decided to use them on his old Minolta SRT Super again.

I already ordered a 55mm adapter so I could use the 50mm for some reversing ring macro on my Pentax, as it is far better than my current 50mm for macro. I am hoping I can coax the 135mm to work for this as well, but it seems to have an EXTREMELY close focusing distance when reversed.

Please let me know if there is a way to make this work. A lot of sites I have seen have said things about the focal plane needing the Minolta lenses to be shaved, but with the 50mm when held up to my K100d, it seemed fine, even at infinity. So any clarification on that would be appreciated as well. Thanks so much guys, and sorry for the long windedness.

10-11-2010, 04:45 PM   #2
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The registration distance is shorter than Pentax uses, so you can't use them without an optical adapter.

The lenses are basically useless unless you use an old Minolta camera (the registration distance is different than what the current Sony Minolta mount uses.

Minolta Lenses on Pentax - Pentax Forum
10-11-2010, 04:51 PM   #3
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QuoteOriginally posted by soppy Quote
is there a way to convert these to the Pentax mount without shaving them down?
No. Here is why. The distance from lens mount to frame (film or sensor) is called the registration. Longer-registration lenses can be put on shorter-registration cameras and can still focus to infinity. Shorter-reg lenses on longer-reg cameras can't. Canon's mounts are shorter than most, so Nikon and Pentax and Minolta lenses can be mounted there. But you're out of luck. Minolta register: 43.7mm. Pentax register: 45.46mm. About 2mm must be shaved off to achieve infinity focus.

I think optical adapters exist, but while they don't exactly suck, they do diminish the image quality, spoiling whatever was special about the lenses. They also act as short teleconverters, stretching the focal length. A non-optical adapter could be cobbled together, but the adapted lens would only focus for closeups. Or you can just reverse them and use them for macros, as you're doing. Oh yeah, the working distance for a reversed lens is its register: 43.7mm.

I know where you're at. I inherited some fine Minolta MC glass that I can't adapt or otherwise use except for closeups. I could sell the lenses, because Canon and Panasonic and Olympus users can mount them on their short-register bodies. But I'll wait till next year when the sales prices will be better.

I'll repeat some advise I got: Put them on the SRT-101 and run some film through it. Good luck!
10-11-2010, 05:02 PM   #4
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Yeah I was just about to say, I'll stick to using them for Macro and probably pick up some film and see how I fare without all the digital help. Time to bust out the 30 year old manual to find out how to work the thing lol. Thanks for the replies guys, much appreciated.

10-11-2010, 05:39 PM   #5
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I've got an adapter en route from Hong Kong even as we speak. I've only got two lenses, one of which is that marvellous Rokkor 50mm f/1.4 (MC) and the other a Formula 5 (??) 200mm f/3.5 (this was bought for me as a birthday present, it worked beautifully on the old film cam but I've no clue about its heritage or reputation).

I don't expect to get the same quality, I keep hearing that the addition of glass to the adapters makes the quality "less", but given that my film cam (an SRT303) is defunct and serving only as a place to locate the Rokkor (I have no cap for its rear) I reckon I have nothing to lose by having spent $30 on something which can get these lenses back into use again.

I'll post some shots when I can.
04-12-2011, 09:00 PM   #6
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Hi Kyteflyer, just wondering how the optical adapter worked for you?
Thanks man.

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