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01-29-2013, 03:42 PM   #1
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"A" Series 28/135 Zoom on a Spotmatic?

As I've previously mentioned on the forum, many years ago I was right into LX, I had all the accessories etc, & one of the lenses I used, was the A28/135 zoom, a really big piece of glass, quite heavy, but it suited most of my needs, & was the lens I was able to use covering most situations. I sold all of my LX stuff/lenses years ago, but kept my mint SP11, & then I bought a ES11.
If I ever see a M42 45/125 zoom, mint with all access, case etc, I may purchase it, but another alternative would be the A28/135?
So, I was just wondering that if I bought the genuine Pentax M42 to K Mount "converter" (which one should I get?), how would the 28/135 work on my two Spotmatics.....would the exposure/focussing systems etc work the same with this lens as with M42 items?
Thanks, Pickles.

01-29-2013, 03:57 PM   #2
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That would be very cool, but I don't think it's possible. You can adapt a screwmount lens to fit a K-mount camera, but not the other way around, AFAIK.
01-29-2013, 03:59 PM   #3
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You can't really go the other way (K to M42) without some surgery. The first K mount cameras are pretty closely related to the late Spotmatics, so maybe an extremely clever parts swapper could make a K-mount Spotmatic, or change the lens mount, but it would be a lot easier to get something like a KM and use that.
01-29-2013, 04:30 PM   #4
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Just get a KX or MX. Even a K2 should be less than $150 (plus a likely necessary CLA). M42 lenses are easily adapted to a K-mount camera but the reverse isn't possible, the mouth opening isn't wide enough. The adapter would have to be outside the body, and that makes the flange focal distance too long.

01-29-2013, 07:40 PM   #5
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You can save some on the A28-135, though, once you find one. Despite your recommendation, mine didn't sell for a lot, and I believe one went pretty cheap here recently. How many Pentax lenses can you buy for only 16.4 grams per dollar? That's would be $10 for an A28/2.8
01-29-2013, 09:00 PM   #6
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The diameter of the K mount is slightly larger than the diameter of the M42 lens. It was purposely designed in this way, so that the K to M42 adapter could fit inside of the camera's K mount bayonet opening, thereby allowing the M42 lens to screw into the adapter. In this way the M42 fits flush with the K mount adapter and the camera's K mount. This design ensures that the M42 lens maintains the proper reregistration distance and thus will be able to achieve infinity focus.

Some (non original Pentax) adapters have a flange that sits on top (or outside) of the camera's mount and these are the adapters that interfere with the M42 lenses ability to focus to infinity, since the registration distance is artificially lengthened (by the width of the adapter's flange).

Unfortunately, this design does not support the reverse, since the K lens would be too wide for the M42 mount opening of the Spotmatic.

Hope that helps.

01-29-2013, 10:05 PM   #7
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Thanks so much, all of you, for your replies. I now understand very well, that it CANNOT, happen!
Cheers, Pickles.

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