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11-17-2009, 05:05 PM   #1
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Modify a 50mm 1:1,2

I have both a Pentax M 50mm 1:1,2 and a A 50mm 1:1,7
And i want to use the 1:1,2 with most ease on my K-m.. Is it possible to rebuild the lenses so i get the 1:1,2 with automatic and the 1:1,7 without? with the parts that i have within the two lenses?
I dont have the lenses with me now so i cant inspect them,sorry is it is a stupid question..hehe

11-17-2009, 05:11 PM   #2
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Don't do it.

It's not a simple case of drilling a few holes in the lens mount to add electrical contacts. The aperture actions of the two lenses are different.

Modifying M-lenses into A-lenses have been topics of many threads. No one has reported a successful case yet.
11-17-2009, 05:11 PM   #3
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Not so much what you need to do with the lenses, but rather what you need to do to your cam:

vietlh81: How to convert the K-M lens to KA lens
11-17-2009, 05:15 PM   #4
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QuoteOriginally posted by RawheaD Quote
Not so much what you need to do with the lenses, but rather what you need to do to your cam:

vietlh81: How to convert the K-M lens to KA lens
Does anyone know if there's any adverse effect on doing this when using a normal A lens? Would be interesting if I can use this method on my M40/2.8

11-17-2009, 05:20 PM   #5
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QuoteOriginally posted by Andi Lo Quote
Does anyone know if there's any adverse effect on doing this when using a normal A lens? Would be interesting if I can use this method on my M40/2.8
The adverse effect is that it doesn't work.

Sure, you can trick the camera into thinking that the K lens is a KA -- you still don't get accurate control of aperture from the body.
11-17-2009, 06:22 PM   #6
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the bottom line is that you will be ruining a lens worht hundreds of dollars to create a lens that does not perform worth a s#!% in A mode.

I converted a 50mmF2 (XR Rikinon) to an A lens by adding an A contact and coding the apertures to match the correct KA lens contact pattern.

did it function, yes, but metering went from -1 stop under exposed to +2 stops over exposed due to the above mentioned differences in aperture control.

It just is not worth it.


If you go out and get an SMC-A 50mmF1.4 it will cost less than the devaluation of the SMC-50mm F1.2
11-17-2009, 06:55 PM   #7
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QuoteOriginally posted by Balticthor Quote
I have both a Pentax M 50mm 1:1,2 and a A 50mm 1:1,7
And i want to use the 1:1,2 with most ease on my K-m.. Is it possible to rebuild the lenses so i get the 1:1,2 with automatic and the 1:1,7 without? with the parts that i have within the two lenses?
I dont have the lenses with me now so i cant inspect them,sorry is it is a stupid question..hehe
BTW, there is no "M" version of the 50/1.2, although there was a "K" (officially, just called "SMC Pentax"). So I assume that's the one you have, and not in fact an "M" lens? Not that I think that you are making this mistake, but many people confuse 1:2 with 1.2...
11-17-2009, 11:46 PM   #8
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QuoteOriginally posted by RawheaD Quote
Not so much what you need to do with the lenses, but rather what you need to do to your cam:

vietlh81: How to convert the K-M lens to KA lens
I don't know how current that site is, however it's saying that doesn't work on digital

11-18-2009, 12:55 AM   #9
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As the others said above, it's not as simple as just adding an A contact.

I tried that on my K50/1.2 lens: drilled a hole at the right location, put an A contact there. The camera recongnized the lens as an A lens, but when I used the rear wheel (on my K7 camera) to adjust/control the aperture, the metering wasn't as expected from an A lens. It did stop down the lens though, but the aperture I set on the camera wasn't really the one I got from the results. Sometimes the metering could be way off.

After that trial, I gave up on the idea and just keep using the lens as a full manual one instead.

Last edited by frank; 11-22-2009 at 09:39 PM.
11-20-2009, 03:46 PM   #10
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Hmm..so a couple of people already tried this.
..and all the while I thought that nobody has and wanted to have a go at it myself!
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