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07-28-2011, 05:25 PM   #1
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Can someone help ID this mount?

I'll try to post a shot of it shortly, but it basically looks exactly like a K-mount except instead of a bayonet, it has a small round rod. The lens even fits on my camera and focuses to infinity as any K-mount lens should - except this thing seems to not want to close down its aperture at all. Turning the aperture ring does nothing, as does fiddling with the rod that normally would be where a bayonet would be located.

So is this a broken K-mount lens, or did I somehow get something entirely different (yet close)?

FWIW, it came mounted on an A3000 camera. I was interested in the lens rather than the body, but I'm wondering if I didn't wind up with a body being more than the lens situation here. I paid hardly anything, so I'm not returning it or anything, but I'd like to know if the lens itself is salvageable either by replacing the mount or going in and fixing what may be broken.

The lens in question is an Underground 28mm f2.8.

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Last edited by Sagitta; 07-28-2011 at 05:44 PM.
07-28-2011, 07:57 PM   #2
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Ka mount

compatibility chart

http://www.mosphotos.com/PentaxLensCompatibility.html

http://kmp.bdimitrov.de/technology/K-mount/Ka.html

http://www.mosphotos.com/PentaxLensesExplained.html

Last edited by Clicker; 07-28-2011 at 08:05 PM.
07-28-2011, 08:15 PM   #3
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So it SHOULD be working then, but is not. I'm guessing the aperture is broken somehow?
07-28-2011, 09:06 PM   #4
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That thing looks more like an MD (or MC) Minolta mount to me.


Last edited by Blue; 07-28-2011 at 09:20 PM.
07-29-2011, 12:04 AM   #5
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Check this:

SLR Lens Mount Identification Guide

Also, try posting a straight shot of the mount - it's hard to make out details from this angled shot. I noticed a pin and that's about it.
07-29-2011, 12:37 AM   #6
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QuoteOriginally posted by Laurentiu Cristofor Quote
Check this:

SLR Lens Mount Identification Guide

Also, try posting a straight shot of the mount - it's hard to make out details from this angled shot. I noticed a pin and that's about it.
Straight on it looks exactly like a K mount - except instead of a bayonet it has that funky pin. I'll try to post a better shot in the AM - its getting late and I need to head off to bed here.

EDIT: I just checked, and the lens apparently WILL stop down on the A3000 (or at the least it will change the exposure settings as I twist the aperture ring)... so I have a lens that will work with an old Pentax film camera but won't work with a modern DSLR. Weiiirrrrrd. I also tried an old Pentax-M 50mm f2 and it worked the same way on the A3000, so I guess I just have a lens that won't behave with a modern camera here.

Last edited by Sagitta; 07-29-2011 at 12:48 AM.
07-29-2011, 05:33 AM   #7
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I really don't think that is a K-mount lenses based on the post looking aperture lever which looks like a giant pin. I agree a pic from the mount end is needed.
07-29-2011, 05:51 AM   #8
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QuoteOriginally posted by Blue Quote
That thing looks more like an MD (or MC) Minolta mount to me.
That was my first reaction, but OP says it fitted onto a PK camera, which an M/MD lens would never do. Does one of the bayonet blades have a notch in it? If so, it's definitely M/MD. BTW that round pin is an aperture pin, not a bayonet. On a PK or NI or various other mounts it would be a flattened flag, not a pin. I've never seen a round pin on a PK lens -- but I haven't seen every single PK-mount lens, so ?quien sabe?

07-29-2011, 06:01 AM   #9
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QuoteOriginally posted by RioRico Quote
That was my first reaction, but OP says it fitted onto a PK camera, which an M/MD lens would never do. Does one of the bayonet blades have a notch in it? If so, it's definitely M/MD. BTW that round pin is an aperture pin, not a bayonet. On a PK or NI or various other mounts it would be a flattened flag, not a pin. I've never seen a round pin on a PK lens -- but I haven't seen every single PK-mount lens, so ?quien sabe?
The minolta does have notch it one of the blades. I have a MC and MD on hand and both have the notch. They definitely would be too small to make attachment to the Pentax film body. Also, the alignment dot on the lens pic appears in the wrong orientation. To that aperture pin/post. I don't know much about Petri but they also have post like pin for the aperture.
07-29-2011, 10:42 AM   #10
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QuoteOriginally posted by Blue Quote
The minolta does have notch it one of the blades. I have a MC and MD on hand and both have the notch. They definitely would be too small to make attachment to the Pentax film body. Also, the alignment dot on the lens pic appears in the wrong orientation. To that aperture pin/post. I don't know much about Petri but they also have post like pin for the aperture.
Yes, Petri also has a pin -- those on my 55/1.8 and 35/2.8 (I have had two of each) are thinner. Both also have a 6mm-high metal rim; the pin sits just inside that, and none such is visible in the photo above. The Petri bayonet has a small notch next to its index pin; the bayonet is too large to fit in a PK mount, and the blades are shorter. The lack of the rim rules this one out as being Petri IMHO. Until we see a better picture, I'll say this one is M/MD (Minolta).
07-29-2011, 10:54 AM   #11
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Older Minolta MC/MD

A clearer picture may help, but the rounded aperture pin indicates Minolta MD/MC to me - I've not seen this type of pin anywhere else.
07-29-2011, 11:09 AM   #12
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QuoteOriginally posted by RioRico Quote
... Until we see a better picture, I'll say this one is M/MD (Minolta).
Total sidebar:
If I ever try to teach someone photography, when they start to act like they know everything, I'll ask them to photograph a lens mount. It's a tricky subject.

My guess is, it's a K-mount, the maker saw no reason that round pins wouldn't work for an aperture lever (me neither) and the blades are stuck. The A3000 has an uncrippled mount, so it can read the position of the lens's aperture ring and adjust exposure. Amazing tech that was not included on Pentax DSLRs.

I've seen Undergrounds on eBay but never heard of anyone using one.
07-29-2011, 12:38 PM   #13
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Newer shot here. Futzed with the levels so the details could be seen in the image. I think Just1MoreDave is right about it just being a bizarre K mount with stuck blades - holding the thing up next to another lens, everything looks the same except for that crazy pin in lieu of a bayonet.

07-29-2011, 01:11 PM   #14
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QuoteOriginally posted by Sagitta Quote
Newer shot here. Futzed with the levels so the details could be seen in the image. I think Just1MoreDave is right about it just being a bizarre K mount with stuck blades - holding the thing up next to another lens, everything looks the same except for that crazy pin in lieu of a bayonet.
I am going to rule out the MD/MC mount of Minolta. However, it has some similarities to K-mount. However, the small lug next to the lever(pin) seems to be filed down or small to non-existent. There is a possibility that someone put a pentax mount on another lens, perhaps even an MD. It does have the slot and slider like a k-mount.


Edit: Here is what an Underground 28mm k-mount is supposed to look like.

http://cgi.ebay.com/Pentax-fit-Underground-28mm-f2-8-lens-PK-mint-/170656026...item27bbe44ea4

Last edited by Blue; 07-29-2011 at 01:52 PM.
07-29-2011, 01:48 PM   #15
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QuoteOriginally posted by Blue Quote
I am going to rule out the MD/MC mount of Minolta. However, it has some similarities to K-mount. However, the small lug next to the lever(pin) seems to be filed down or small to non-existent. There is a possibility that someone put a pentax mount on another lens, perhaps even an MD. It does have the slot and slider like a k-mount.
Yes, a better picture, and I agree with you, it could be a mod. I've seen numerous PK lenses but none with a round pin. I *have" seen M/MD lenses with a flat flag, from 3rd-party makers, not from Minolta.

So for instance my Kiron-made 85-210/4.5 has a flat flag -- Kiron likely didn't rebuild the entire assembly for similar mounts (where the aperture-link flags move in the same direction), but just changed the bayonet piece and called it good. (Nikon flags move in the opposite direction.)

QuoteQuote:
Edit: Here is what an Underground 28mm k-mount is supposed to look like.
Did you mean to insert a photo here?

Darn, now I'll have to gargle for UNDERGROUND PENTAX and look for pictures of lens butts. Grumble...
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