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04-18-2009, 05:16 PM   #1
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How to stop down an M42 on a K-mount camera

Sorry for the newbie question but this has been bugging me. I have several m42 lenses, some of them Takumars. Anyway I want to mount them on my Program Plus, Super Program, KM, ME Super (and others) cameras. I know the automatic/aperture priority functions won't work using these lenses, but what is the step by step procedure to use these lenses on the k-mount cameras shooting in the cameras' manuals modes by "stopping down" the lens?

If I use my m42 lenses with the manual/auto switch, do I just put the lens on manual mode switch? What about some of my m42 lenses that do not have such a switch on the lens. I have a Mamiya SX lens that does not have the manaul/auto switch.

BTW, I do have a genuine Pentax lens adapter.

04-18-2009, 06:32 PM   #2
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For lenses with the switch, just set it to manual. Look through the viewfinder as you move the aperture ring and you can easily see the effect of the blades closing down.
04-18-2009, 06:59 PM   #3
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QuoteOriginally posted by scimitar12 Quote
Sorry for the newbie question but this has been bugging me. I have several m42 lenses, some of them Takumars. Anyway I want to mount them on my Program Plus, Super Program, KM, ME Super (and others) cameras. I know the automatic/aperture priority functions won't work using these lenses, but what is the step by step procedure to use these lenses on the k-mount cameras shooting in the cameras' manuals modes by "stopping down" the lens?

If I use my m42 lenses with the manual/auto switch, do I just put the lens on manual mode switch? What about some of my m42 lenses that do not have such a switch on the lens. I have a Mamiya SX lens that does not have the manaul/auto switch.

BTW, I do have a genuine Pentax lens adapter.
With the switch set to Auto, the aperture will remain open until the aperture pin is depressed. On Manual, the aperture follows the ring even when the pin is not depressed, so you need to set the lens to Manual. Lenses without the Auto/Manual switch are Manual. You can see this with the lens off the camera by turning the ring while looking through the lens.

There is an additional type of lens that appears to have two aperture rings. One of the rings will have detents like a normal aperture ring, but turning it does nothing unless you turn the second ring with it. This is called a preset lens. You calculate the aperture and set it on the ring with detents. The second ring will rotate freely between the preselected aperture and side open. You can flick the ring between wide open and stopped down without looking or counting clicks.
04-18-2009, 08:16 PM   #4
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Thank you for the help. Just the info I was looking for!

04-18-2009, 08:31 PM   #5
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Does Manual mean that the switch is covering the word manual or is the word manual showing?
04-19-2009, 04:24 AM   #6
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QuoteOriginally posted by Fl_Gulfer Quote
Does Manual mean that the switch is covering the word manual or is the word manual showing?
The word (or letter "M") should be showing. This is very easy to verify by merely moving the aperture ring and seeing if the blades move or not.
04-19-2009, 10:59 AM   #7
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Thanks Mike
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