Two reasons for using foil with M42 lenses.

Started Jan 18, 2010 | Discussions thread
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brandrx Forum Pro • Posts: 28,337
Two reasons for using foil with M42 lenses.

The below applies to K20D. K10D and earlier models do not have a Catch-in-focus setting. It is "just" already there with manual focus lenses only. The menu item #36 can be another number or no number in other cameras. It is "Using aperture ring" in the custom menu. The point is: If you have a "Catch-in-focus" setting in your custom menu then set it to = 2. If you have a "Using aperture ring" setting in your custom menu then set it to =2.

The following was written for the K20D. However, except for the item #34 and #36 it should apply to all Pentax DSLR's.

(1) - Go in to the custom menu item #34 and set to = 2. Also set custom menu #36 to = 2. Now leave both of these setting at = 2 and you will never have to even think about them again. Item #34 allows you to do Catch-in-focus (aka focus trapping). Item #36 allows you to use K, M, and M42 lenses, also A type lenses when used in the non-A position. Without menu item #36 = 2, you will not get the request for entering focal length at turn-on. In fact, you will not be able to use K, M, or M42 lenses at all.

(2) With menu itme #36 set = 2 then you can now use the M42 lens and get focus confirmation. However, even if you do not have focus confirmation you can still take the shot, OOF, even if you have AF-S selected. To correct this minor malfunction, that is the reason for the foil. See (3) below.

(3) There are two reasons for using aluminum foil, or scraping the paint off the rear of the lens. Reason #1 - You can use the M42 lens to do Catch-in-focus. With the switch on the side of the camera set to AF-S the shutter will not fire unless the lens is in focus. Reason #2 - You can use the M42 lens with the Pentax-F 1.7X AF Adapter.

I hope this helps.


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'Every day when I get up the first thing I do is grab one of my Pentax DSLR cameras and run to the mirror just so I can start the day off with a double dose of beauty.' ~ brandrx

Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

Ron ~ Retired.

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