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02-09-2010, 09:47 AM   #1
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Crazy idea: M-A hybrid?

would it be possible to make a hybrid M-A lens? My idea would be to combine the complete aperture/ring/mount assembly from an A series lens with the rest of a M series lens. Is it possible?

02-09-2010, 09:58 AM   #2
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there have been a ton of threads on conversion of K mount lenses, whether these are SMC or SMC-M lenses, or third party lenses into KA mount

while on film cameras this permitted matrix metering to be used with K mounts. on DSLRs this is not the case.

Mechanically, the aperture on K mount lenses has the diameter change linearly with the activation lever, where on KA mounts it is the area.

as a result, you cannot modify the lens with the contact data and have the AV mode expsoure work correctly.

Several, myself included have tried.

the precision is +/- 1-2 stops.
02-09-2010, 12:16 PM   #3
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I think you misunderstood what I was trying to say.

What I am suggesting is take from an A series lens the entire aperture assembly, linkage, electrical bits, blades, and ring, and somehow install it in an otherwise M series lens. Is it physically possible? Is the construction of, let's say, an M 50 f2 and an A 50 f2 close enough to allow this?
02-09-2010, 12:20 PM   #4
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I take it you in essence want an M lens that can autoexpose?

02-09-2010, 12:41 PM   #5
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QuoteOriginally posted by jboyde Quote
I take it you in essence want an M lens that can autoexpose?
Basically. I think the M lenses are better looking and more durable, but I want to have the auto functionality.

Lets put it this way, if money wasn't an issue I'd go Zeiss or Voigtlander and be done with it.
02-09-2010, 01:08 PM   #6
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QuoteOriginally posted by Steve Beswick Quote
I think you misunderstood what I was trying to say.

What I am suggesting is take from an A series lens the entire aperture assembly, linkage, electrical bits, blades, and ring, and somehow install it in an otherwise M series lens. Is it physically possible? Is the construction of, let's say, an M 50 f2 and an A 50 f2 close enough to allow this?
All you really want to replace is the outer plastic bits of the A lens with the equivelents from the M lens. If you have the same models of A and M lenses then try it and let us know who it goes.
02-09-2010, 01:14 PM   #7
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QuoteOriginally posted by MattGunn Quote
All you really want to replace is the outer plastic bits of the A lens with the equivelents from the M lens. If you have the same models of A and M lenses then try it and let us know who it goes.
Huh. I didn't think of doing it that way.

Now all I need is a little free time and two lenses!
02-09-2010, 01:22 PM   #8
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QuoteOriginally posted by Steve Beswick Quote
I think you misunderstood what I was trying to say.

What I am suggesting is take from an A series lens the entire aperture assembly, linkage, electrical bits, blades, and ring, and somehow install it in an otherwise M series lens. Is it physically possible? Is the construction of, let's say, an M 50 f2 and an A 50 f2 close enough to allow this?
you're right

I mis understood.

OK, I get the point of what you want to do, but unless the aperture assembly is from the same focal lenght lens it will ot be sized correctly.

Unless the A series lens was destroyed, I would be more in favor of taking the M series elements out and mounting them in the A series lens body. That is, of course, assuming the lenses internally are the same. I don;t think they are.

02-09-2010, 01:36 PM   #9
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Unless you got the A lens for free it seems like a bit of a waste to turn two lenses into one

Also, A lenses are built pretty damn well. Except for maybe the 50/2 and 50/1.7.
02-09-2010, 02:23 PM   #10
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Easier way

What you can do else is to make the camera just act like it has a A-series lens attached by closing the contact between lens and body. I'm using it on all my non-A lenses and it works just fine.
Here' an older article that shows how to do:
vietlh81: How to convert the K-M lens to KA lens
And here my own which should be updated but still everything written there works.
https://www.pentaxforums.com/forums/do-yourself/73144-how-make-non-lens-work-like-lens.html
But by now I'm only using them semi-automatic meaning that I have full A-lens features but still a manual aperture ring. Works great except for really fast lenses - doesn't work on my SMC 50 so I use it as if it were a M42 lens. Don't fully mount it so aperture is fully independent of the camera.
02-09-2010, 02:25 PM   #11
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I don't think it'll work. You might get extremely lucky and find some pair of lenses that are close enough, but I would not risk a lot of money on it. Here's one example, the M and A 50mm f1.7s:



The aperture mechanism that you can partly see on the right is upside down and concealed on the left. Not even the five chrome mount screws are the same. I'd say except for the elements, these two have no common parts, and I'm not sure about the elements. If you had a late M design, maybe, like a late M50/2 built in Taiwan - but you wouldn't gain much in construction, since those lenses had already started using more plastic.
02-09-2010, 02:28 PM   #12
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QuoteOriginally posted by Just1MoreDave Quote
I don't think it'll work. You might get extremely lucky and find some pair of lenses that are close enough, but I would not risk a lot of money on it. Here's one example, the M and A 50mm f1.7s:



The aperture mechanism that you can partly see on the right is upside down and concealed on the left. Not even the five chrome mount screws are the same. I'd say except for the elements, these two have no common parts, and I'm not sure about the elements. If you had a late M design, maybe, like a late M50/2 built in Taiwan - but you wouldn't gain much in construction, since those lenses had already started using more plastic.
dave, I would agree, maybe make an A lens that was really bad with fungus or damaged elements by swapping the M elements.

by the way, it looks like a lot of oil in the M lens you show. this should be dry. how are the aperture blades?
02-09-2010, 02:38 PM   #13
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QuoteOriginally posted by Just1MoreDave Quote
I don't think it'll work. You might get extremely lucky and find some pair of lenses that are close enough, but I would not risk a lot of money on it. Here's one example, the M and A 50mm f1.7s:



The aperture mechanism that you can partly see on the right is upside down and concealed on the left. Not even the five chrome mount screws are the same. I'd say except for the elements, these two have no common parts, and I'm not sure about the elements. If you had a late M design, maybe, like a late M50/2 built in Taiwan - but you wouldn't gain much in construction, since those lenses had already started using more plastic.
Those photos confirmed my fears. Bummer. Thanks for the photos!
02-09-2010, 04:56 PM   #14
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QuoteOriginally posted by Lowell Goudge Quote
dave, I would agree, maybe make an A lens that was really bad with fungus or damaged elements by swapping the M elements.

by the way, it looks like a lot of oil in the M lens you show. this should be dry. how are the aperture blades?
It's not unusual to have grease there; the inner surface of the aperture ring is greased. I think it's pretty typical to take the mount off a Pentax lens and have it look like that. The aperture blades are fine, probably for three reasons:
  • I might be right about the grease being OK. Just look at the amount of exposed grease in your M100/4 (from the really long focus helix) sometime.
  • The M50/1.7's blades are really well shielded from oil migration, even better than other Pentax lenses, which are generally better than third-party lenses.
  • This lens is not really worth selling because it's got a tiny chip in the front element and it's a bit worn looking. I have an F50/.7 so I don't take photos with it. It just sits in a drawer until I take it apart to show photos of something. It's usually at 68-78F. Remind me this summer and I'll leave it in my truck on the dashboard for a week. That should be a good test.
02-09-2010, 11:05 PM   #15
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QuoteOriginally posted by Just1MoreDave Quote
It's not unusual to have grease there; the inner surface of the aperture ring is greased. I think it's pretty typical to take the mount off a Pentax lens and have it look like that. The aperture blades are fine, probably for three reasons:
  • I might be right about the grease being OK. Just look at the amount of exposed grease in your M100/4 (from the really long focus helix) sometime.
  • The M50/1.7's blades are really well shielded from oil migration, even better than other Pentax lenses, which are generally better than third-party lenses.
  • This lens is not really worth selling because it's got a tiny chip in the front element and it's a bit worn looking. I have an F50/.7 so I don't take photos with it. It just sits in a drawer until I take it apart to show photos of something. It's usually at 68-78F. Remind me this summer and I'll leave it in my truck on the dashboard for a week. That should be a good test.
You can leave that lens in my truck for a week - just don't be surprised if it disappears in that time!
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