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05-15-2011, 11:54 AM   #1
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use of screw mount lenses on K-x

Hello,
I have a K-x and have a screw mount adapter. I've put on a Fujinon screw mount lens on the K-x but from my understanding, I cannot control the aperture. I am stuck at 1.8.

Am I correct or am I doing something wrong?

Are there old screw mount lenses that can be installed on K-x whose apertures can be changed?

Thank you for your time and help.

05-15-2011, 11:58 AM   #2
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You have to use the aperture ring on the lens to adjust the aperture. Then, follow these instructions to meter: https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html

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05-15-2011, 01:02 PM   #3
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The fujinon lenses don't have an auto/manual switch like Takumars - you're going to have to rig a way to keep the aperture pin on the lens base permanently depressed. often you can take off the rear mount to access the mechanism.
05-15-2011, 02:02 PM   #4
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For what its worth - On my lens (different lens but same problem), I hold the pin in with aluminium tape (available at hardware stores).
I cut a piece the right shape over the pin (with a reasonable area to stick on) and then coloured black with a permanent marker.

Works well for me - had it on for over a year now and no sign of it wanting to let go. If your lens does not have sufficient area to stick the tape down (the Auto Takumar 35 f3.5 does) then it may not work.

05-15-2011, 10:57 PM   #5
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Thank you so much for the replies. It never crossed my mind to just keep the pin in with something, so that is actually very helpful. And thank you for the link.

Another question: If I'm understanding correctly, there are lenses that do not need to be "rigged," whose apertures can be controlled through the controls of the DSLR?

If so, when browsing for lenses, how do you know which ones those would be?

Thank you again.
05-15-2011, 11:15 PM   #6
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I've tried taping down the pins but it doesn't work for me. Some adhesives hate me.

No, screwmount lens apertures cannot be controlled by ANY cameras -- except maybe some variant M42 systems with specific film bodies and lenses, maybe those with extra pins. Standard M42-auto lenses only have the single pin, which stops-down the lens to the aperture you've set. So the most an M42-auto camera can do is stop-down the aperture. The user must still twist the aperture ring themself. That's so on dSLRs also. The bodies just have no way to change the f-stop.

I own a K20D, a couple PK-mount film cameras, and several M42-mount cameras, some with aperture automation (auto stop-down) and some without. I have stopped buying M42-auto-only lenses because they only function fully on M42-auto film bodies. Otherwise, they're a pain.

Note: I've read of a costly M42-PK adapter with an internal flange that holds the pin in. No in-camera aperture control, but at least auto-only M42's would be usable on dSLRs. Maybe I'll look for one of those, when I have money again.
05-16-2011, 01:35 PM   #7
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RioRico, the foil tape I have (cheap from hardware sore) has industrial grade adhesive that really sticks. The foil is thick enough to stay fairly flat.
So I guess it depends on the brand etc.
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