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03-16-2015, 09:28 AM   #1
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How do you enable green-buttoning with non-proper-metallic mounts again?

I tried a search but my search-fu is weak.

I have an old cheap (actually, it probably cost me negative dollars) lens but it has a black plastic and metal mount on it. Whatever the material is, its not making proper contact with the electronics on the camera, so I need to figure a way to allow it to do so (short of swapping mounts, which I don't want to tackle here). I know you can put tinfoil between the lens and mount, but is there a better, more permanent solution I can employ? If so... what?

This isn't a lens I want to sink any huge amounts of time into, but it would be nice to see how it behaves if I can get it to stop down.


Last edited by Sagitta; 03-16-2015 at 04:37 PM.
03-16-2015, 09:38 AM   #2
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Well, if it is plastic then you can't "scrape off the black" like you can with anodized mounts. So I'd go with foil or copper tape. There is such a thing as conductive paint/ink, but I think it would probably get scratched off and create dust that could get into things. Foil tape is easy enough, will only increase the cost of the lens by a couple of bucks, and generally is permanent if you are careful with it. (It increases the friction, so it tends to get squeezed and adhered pretty well.)
03-16-2015, 09:53 AM   #3
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Original Poster
QuoteOriginally posted by vonBaloney Quote
Well, if it is plastic then you can't "scrape off the black" like you can with anodized mounts. So I'd go with foil or copper tape. There is such a thing as conductive paint/ink, but I think it would probably get scratched off and create dust that could get into things. Foil tape is easy enough, will only increase the cost of the lens by a couple of bucks, and generally is permanent if you are careful with it. (It increases the friction, so it tends to get squeezed and adhered pretty well.)
I tried sticking tinfoil in there, and it only half worked. I started getting prompts for dropping the lens down to f/1.2 (I wish...) as well as adjusting aperture and the like, but nothing was happening when I tried metering. I'll have to pick up some proper tape somewhere and see if that solves anything. I'd be more annoyed if the lens was actually worth anything, but so far... meh.

I suspect its a Cosina rebadge of some sort (this one is branded Promaster - its an 85-210 macro zoom). Since I paid basically nothing for the lens (part of a $12 lot win on fleaBay, part of which was a 50mm f/1.4...) I'm not really upset more than I'm mildly annoyed about the situation with the lens.
03-16-2015, 09:55 AM   #4
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Tape will work much better. Another option is just to remove the lever and then it will work like an m42 and you stop down yourself with the ring. (And you can use Av mode)

03-16-2015, 10:15 AM   #5
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What camera are you using that makes a difference. Some bodies still make a meter reading even though doesn't stop down. Lenses like this with a black mount are a bit like a t-mount but those don't have an aperture lever. All the old early PK's with a black mount I have encountered were metal bayonets. But scraping off the black anodising tends not to leave a clean enough surface for consistent connection. Note that it is just the data connection you need to short see here.
Overall I'm with vonBaloney.
03-16-2015, 12:27 PM   #6
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Foil tape is your best bet. It is only a semi-permanent solution as the tape will eventually peel off from being rubbed during mounting and dismounting. You can find foil tapes at auto parts stores. As noted before you only need to short out the 7th or data pin.

Your tin foil must be intermittently shorting the "A" pin as otherwise you should just have the F- - in the viewfinder. With all the pins shorted the body is signaled that a the max aperture is f/1.2 and the min is f/22
03-17-2015, 11:19 AM   #7
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QuoteOriginally posted by Not a Number Quote
As noted before you only need to short out the 7th or data pin.
I am quoting this last for emphasis. Shorting any of the other contacts, particularly the "A" contact may cause unpredictable results.


Steve
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