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11-09-2010, 06:44 AM   #1
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A*85/1.4 weird electrical contacts

I just came across an A*85/1.4 lens having a pretty strange bayonet mount. Its electrical contact pattern is that of a 1.2-22 lens (no plastic isolators, A-Pin only) instead of that of an 1.4-22 lens, which does have one plastic contact
(see figure 2 and table 1 on Features and Operation of the Ka Mount for the different contact patterns).
Mounted on a camera it shows a maximum aperture of 1.2. The aperture blades do not close until something smaller than 1.4 is set though, so it really is not an 1.2 lens .

I took a comparison picture with an A50/1.4 on the left and an A50/1.2 on the right.
Looking at the A50/1.4, there is the A-Pin and one plastic contact. The two extra contacts on the A50/1.2 are made of metal, so the resulting pattern is the same as on the blank A*85 in the middle.
Also notice the shape of the slot at the base of the aperture lever which is straightened on both the A*85 and the A50/1.2 but not on the A50/1.4.

Now, what the heck is this mount and where does it come from? It is not that of an A50/1.2 unless there were some of them produced without the two extra metal contacts. Was it maybe coming out of the Pentax factory this way? Has anyone ever heard of other SMC-A lenses having a wrong contact pattern?

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11-09-2010, 06:53 AM   #2
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Hmm, that is pretty strange! I don't have a copy of the lens handy right now, but I can check how it behaves later on!

One thing is for certain- there are a few A lenses which chronically under- or over-expose on DSLRs. Either there's a hardware limitation somewhere, or the internal lens data for certain A lenses is off.

I tested the A 15mm F3.5 on the K-7, K10 and MZ-S and both overexposed by one stop whenever the lens wasn't wide-open. The super program and pz-1 didn't have this problem, however!
11-09-2010, 07:05 AM   #3
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Now that you mention it: Compared to green-button-stop-down-metering the lens overexposes about 1/2 stop when the aperture ring is set to A except for that "virtual" 1.2. I suppose this is due to the wrong contact pattern, at least that would make sense to me since the camera assumes an 1:1.2 lens wide open for calculating the exposure.
11-09-2010, 07:09 AM   #4
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Sounds like someone performed a repair on that lens with a 1.2 mount instead of a 1.4 mount...

11-09-2010, 07:28 AM   #5
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Or someone was trying to modify the lens to mount on a Canon or Nikon.
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11-09-2010, 07:29 AM   #6
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QuoteOriginally posted by Clinton Quote
Sounds like someone performed a repair on that lens with a 1.2 mount instead of a 1.4 mount...
That's what I thought at first, but the 50/1.2 is the only A1.2 lens I know of. Do samples of the A50/1.2 without those two extra metal contacts exist? Or is it possible to get blank mounts with that specifically shaped slot from somewhere else?
11-09-2010, 07:36 AM   #7
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My A* 85/1.4 has one insulated contact like your photo on the left.

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11-09-2010, 11:20 AM   #8
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What about the shape of that aperture lever slot? For this lens the plastic part of it is shorter than the metal part and protrudes a bit (clearly visible on the left side of the slot), they do not really seem to have been made to fit together. But then again, that is the case on the A50/1.2 as well, just not by that much...


Anyways, does this lens have some extra value for collectors now?

11-09-2010, 02:18 PM   #9
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I think you have a modified non-A mount. The hole of the A-pin is different to other the hole on other A-lenses.

My A*85 have 1 isolated, the A-pin and one metal-pin.

I have the A50mm 1.2, A*85mm an A*135mm all have this shape of that aperture lever slot. But the shape of your A*85mm is a little bit different.

If you have problems with metering, i would try to build the isolated pin.
11-09-2010, 03:16 PM   #10
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You are right, it looks a bit different on this picture but I guess that is just because the A* lens was not set to "A" whereas the other lenses were. So the pin was recessed.
When I compared the pins on the actual lenses, they looked perfectly identical to me. But maybe I can take some close-ups later, so you guys can take a look as well.

However, are there any non-A mount lenses out there having such a lever slot shape? Since all of my K lenses and 50% of my M lenses have a mount locking notch that extends to the edge of the lens mount (it was changed at some point if I remember correctly), there cannot be that many lenses to choose from.
The plastic part could have been swapped since the screws always seems have the same position, but I can hardly imagine anyone being able to shape the metal part without any optical flaws from a standard k-mount (and then forgetting about the plastic contact, but that is another story )


In which way does the shape of the slot differ? Any chance you can take a pic of yours? That would be great!
11-10-2010, 06:46 AM   #11
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There you go...
Maybe I should have cleaned the lens before taking pictures

Lens is set to A on the second, third and fourth pic.
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11-10-2010, 02:14 PM   #12
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Here are two shots of my A50mm 1.2:
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11-10-2010, 02:18 PM   #13
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And some shots of my A*85:
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11-10-2010, 04:19 PM   #14
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Thanks a lot, feaverbeaver!

But I am still not sure what you meant by saying that the slot on "my" A* looks different. Your lenses have that plastic ring and lever protection shield removed, but except for that, I cannot see a difference. Is that what you meant? Or am I missing something?
11-10-2010, 06:52 PM   #15
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QuoteOriginally posted by 721 Quote
Thanks a lot, feaverbeaver!

But I am still not sure what you meant by saying that the slot on "my" A* looks different. Your lenses have that plastic ring and lever protection shield removed, but except for that, I cannot see a difference. Is that what you meant? Or am I missing something?
I removed the shield only for the photos of the slot. On the first photo from your A*85 it looked like self made, but on the last photos it looks like the slot on my lenses.
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