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05-18-2012, 07:18 AM   #1
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Plastic Lens Mount and Green Button

I recently got a K-5, my first Pentax DSLR, though not my first Pentax camera. (I own a K1000 and two MX bodies.)

I have read and understood the post by Adam on shooting K and M lenses (without the A capability) using the Green Button and so on. Works great!

So I finally got around to trying out a cheap old used manual focus Vivitar 28mm lens that I own (that works fine with my old film bodies). But the Green Button does not make the body meter; and the DOF Preview function (on the on/off switch) doesn't make the lens stop down. The settings on the top display blinks. Worried, I went and tried my various other lenses (with and without A capability) and everything is OK. Just this 28mm lens doesn't work.

The only thing I can figure out that makes it different from all my other manual focus lenses is that it has a plastic mount. Is the K-5 using the metal mounts of even non-A capable lenses to tell if there's a lens mounted? Maybe the camera thinks there's just a plastic body cap on, so it won't meter. (Though it will shoot wide-open only.)

If so, has anyone gotten past this? Maybe a bit of aluminum tape strategically placed on the lens's mount?

I mean, I can l can live without ever using this lens with the K-5, if I have to. It's not a great lens, so no terrible loss really. But I was surprised to see this happen. Any thoughts?

05-18-2012, 07:23 AM   #2
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No difference if plastic or metal mount . That lense could be defective or missing some contact
05-18-2012, 07:29 AM   #3
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I had trouble with ext. tubes because they were painted black would not recognize there was a lens so I had to sand down to bare metal where it would short the contacts so yes I think the plastic mount is the issue.
05-18-2012, 07:33 AM   #4
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QuoteOriginally posted by bobmaxja Quote
No difference if plastic or metal mount . That lense could be defective or missing some contact
There are no contacts on it at all-- it's a pre-A K-mount lens. Works perfectly fine on non-"crippled" K-Mount film bodies. Only the K-5 won't stop it down for some reason. I don't hear the K-5 even trying to stop it down.

So that's why I'm thinking it's the plastic mount-- I think all the Pentax lenses with plastic mounts also had the A contacts-- which the K-5 would read and know there's a lens attached. Makes some sense to me, anyway.

05-18-2012, 07:35 AM   #5
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QuoteOriginally posted by hangman43 Quote
I had trouble with ext. tubes because they were painted black would not recognize there was a lens so I had to sand down to bare metal where it would short the contacts so yes I think the plastic mount is the issue.
OK, great, someone else who has experienced something similar!

Yeah, no metal anywhere on this cheapie lens mount. Lucky that sanding helped out with your extension tubes.
05-18-2012, 08:19 AM   #6
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The camera doesn't have anything shorting the contacts. You can try to resolve this by using a bit of foil to re-create what others achieve when they sand the paint off. Just stick it between the lens and the camera body contacts and you should be right to go from there
05-18-2012, 08:41 AM   #7
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QuoteOriginally posted by Chaos_Realm Quote
The camera doesn't have anything shorting the contacts. You can try to resolve this by using a bit of foil to re-create what others achieve when they sand the paint off. Just stick it between the lens and the camera body contacts and you should be right to go from there
Definitely worth a shot, for the next-best-thing to free. Sounds like my guess was correct, and this will do the trick. I'll try it tonight...
05-18-2012, 09:03 AM   #8
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Bits of tinfoil get lost when changing lenses. Something a bit more permanent is needed.

A couple years ago I took myself to a hardware store (in a resort town -- no great discounts) and bought a 100-foot roll (just under 2 inches wide) of Nashua-brand metal ducting tape for about US$4. This is shiny on one side, with paper-covered adhesive on the other side. Cheap, and plenty of it.

To use it for CIF purposes etc, I cut strips about 6cm / 0.25in wide, then cut them in half (25cm / 1in long). I peel back the paper and apply a strip to a lens base such that it will cover the A contacts at the 6-8-o'clock positions of the camera mount. I do this with any plastic- or paint-base lens whose base is wide enough to cover those contacts.

This works fine on lenses. DO NOT apply this tape to macro tubes, T-mount adapters, other such pieces with totally flat bases. The thickness of the tape is enough that the piece WILL jam on the mount, more an annoyance than a danger, but still to be avoided. I just use a file to scrape paint from such pieces.
_____________________________________

That's good for CIF (catch-in-focus). But CIF isn't your problem. Your lens won't stop down. I've had various lenses with this problem. It's likely that your lens aperture mechanism needs maintenance or repair.

* Maintenance (1): Look for oil on the iris blades. Any visible oil could make the blades stick together. Some here have successfully disassembled lenses and cleaned the blades. That is beyond my skill level. Have fun!

* Maintenance (2): I had one lens where the iris blades were misplaced, overlapping in such a way that the aperture wouldn't close. I took off the base and slightly pushed the blades, and they snapped into place. I was lucky.

* Repair: Does the aperture ring move freely, with no resistance or click-stops? Then a tiny ball-bearing has escaped its position. Good luck finding it. If you set the aperture to mid-range (around f/8) and push the aperture link, does the iris stay open? Then the linkage is broken. Repair is needed. You now have a subject for surgical exploration, or for target practice.

Manual-mode usage with Green Button to stop-down a lens is entirely mechanical. Electrical contacts (or lack thereof) play no part. Check the mechanics of the lens. Good luck!

05-18-2012, 11:20 AM   #9
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Also copper paint should work, right?
05-18-2012, 11:24 AM   #10
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If it's conductive it will work.

Also, stop down metering WILL NOT work unless the contacts are shorted - the reason is simply because the body will not allow it as it see's there is no lens attached. (On the newer bodies that is, may be different with older digital bodies I can not recall)
05-18-2012, 11:29 AM   #11
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QuoteOriginally posted by joe.penn Quote
If it's conductive it will work.

Also, stop down metering WILL NOT work unless the contacts are shorted - the reason is simply because the body will not allow it as it see's there is no lens attached.
It is usually used as a shield and grounding so yes, it's very conductive. I think it's pretty durable too and I think it would handle the mounting, but I can't say 100%. At least you can paint it thin.
05-18-2012, 01:22 PM   #12
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QuoteOriginally posted by joe.penn Quote
Also, stop down metering WILL NOT work unless the contacts are shorted - the reason is simply because the body will not allow it as it see's there is no lens attached. (On the newer bodies that is, may be different with older digital bodies I can not recall)
I have a PK-M Hanimex 28/2.8 with non-conductive paint on its base. (Serial number starts with 11 so I don't know the maker.) I normally have a strip of metal tape on the base as I described above, for CIF. As a test, I just now removed the tape and mounted the lens on my K20D. M-mode plus Green Button works fine and CIF doesn't. I replace the tape and both work.

So, shorting the contacts is necessary for CIF, but not for stop-down metering and exposure. That's on the K20D. Your camera may vary.
05-18-2012, 01:28 PM   #13
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QuoteOriginally posted by RioRico Quote
That's on the K20D. Your camera may vary.
Kx and K5 it will not stop down without the contacts shorted - I wan't sure if the older bodies were different or not, I too foil the contacts for CIF and for stop-down when using my "non A" extension tubes.
05-19-2012, 02:03 AM   #14
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QuoteOriginally posted by joe.penn Quote
Kx and K5 it will not stop down without the contacts shorted - I wan't sure if the older bodies were different or not, I too foil the contacts for CIF and for stop-down when using my "non A" extension tubes.
the same with K7
05-20-2012, 10:42 AM   #15
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So, I gave it a shot with just a piece of aluminum foil to short out the contacts, as though it was a metal non-A mount. And sure enough, the lens works just fine, just like my other non-A capable K-mount lenses.

QuoteOriginally posted by RioRico Quote
Bits of tinfoil get lost when changing lenses. Something a bit more permanent is needed.

A couple years ago I took myself to a hardware store (in a resort town -- no great discounts) and bought a 100-foot roll (just under 2 inches wide) of Nashua-brand metal ducting tape for about US$4. This is shiny on one side, with paper-covered adhesive on the other side. Cheap, and plenty of it.

To use it for CIF purposes etc, I cut strips about 6cm / 0.25in wide, then cut them in half (25cm / 1in long). I peel back the paper and apply a strip to a lens base such that it will cover the A contacts at the 6-8-o'clock positions of the camera mount. I do this with any plastic- or paint-base lens whose base is wide enough to cover those contacts
I will definitely do this. A cheap hack, and then there's surely other things I could use that tape for around the house.

QuoteOriginally posted by RioRico Quote
That's good for CIF (catch-in-focus). But CIF isn't your problem. Your lens won't stop down. I've had various lenses with this problem. It's likely that your lens aperture mechanism needs maintenance or repair.
No, the lens is fine. Nice snappy aperture blades; stop-down lever moves easily; smoothly functioning aperture control ring; etc. Works just fine with my old K-mount film bodies. It was just the plastic mount fooling the K-5.

QuoteOriginally posted by joe.penn Quote
Kx and K5 it will not stop down without the contacts shorted - I wan't sure if the older bodies were different or not, I too foil the contacts for CIF and for stop-down when using my "non A" extension tubes.
And that was exactly the issue.

Thanks everyone!
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