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03-14-2012, 08:54 AM - 1 Like   #1
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Kr: short contacts to change aperture when using M42 lens ?

Hi,

I am using Pentax K-r with some K mount lens (aka the -M lens) and M42 lens. I'd like to trick the camera so that

(1) I can use the -M lens and M42 lens normally
(2) The camera can see my lens as the -A lens so that I can change the aperture on the body to fix the exif data (instead of remembering or writting them down on a paper.) Surely when I modify aperture settings on the body, the real aperture on the lens won't change. All that I want is to provide a simple way to record the aperture information in the exif data.

I've taken a look on the internet with no success. I want to know some specifications of the K-AF2 mounts (this document Features and Operation of the Kaf2 Mount lacks some details or I must miss them somewhere). If you have any ideas / documents or links, please help .

Thank you very much


Last edited by icy; 03-14-2012 at 08:59 AM.
03-14-2012, 09:01 AM - 1 Like   #2
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You probably want to look at the Ka mount details more than KAF2

Features and Operation of the Ka Mount
03-14-2012, 12:51 PM   #3
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I am not sure there is a way to do this but if you figure it out please post the solution. I am sure several 100 people on this forum would be delighted.
03-14-2012, 01:01 PM   #4
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You would have to short the contacts per the largest aperture of the lens you have mounted, this changes per lens, then also make the A contact. The remaining issue is on k-M lenses the camera moves the aperture lever assuming an A lens is mounted. The movement of the lever is not common for Km and KA lenses so the aperture would not be set correctly on M lenses. On M42 lenses you would have to set both the lens and camera while shooting in manual. You would have to meter with the lens open then change apertures. I would think it would be better to alter the lens. Add a small screw to make the A contact and nail Polish to short the aperture contacts. Good luck let us know how things work

Hans

03-14-2012, 01:02 PM - 1 Like   #5
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I've seen this mentioned on the forum here, but can't find anything offhand. The closest I've found is this mod, which isn't what we want here, but it does discuss which contacts do what. Presumably, fooling the A pin (third from the top, looking at the camera mount) by shorting it would make the camera think it had an A lens on, and let you select the aperture. There may also be other pins that must be insulated rather than shorted.

QuoteOriginally posted by hnikesch Quote
On M42 lenses you would have to set both the lens and camera while shooting in manual.
This is what we're talking about with M and K lenses, too. OP doesn't expect it to set the aperture, just to record the data to EXIF.
03-14-2012, 01:03 PM   #6
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I'm pretty sure this is not possible, though i think the number of people interested would be closer to several thousands if it could be done

m42 lenses don't even cover the contact so not a hope in hell with those attached.

I think before it was crippled as a mount the camera would move a lever to meter to get a read so you didn't need the green button, that disappeared decades before anyone was even thinking Exif

EDIT : I will add the only company that has done something along this line is Leica where they can chip an older lens to identify it AFAIK. and it isn't available for every lens either.

Last edited by eddie1960; 03-14-2012 at 01:08 PM.
03-14-2012, 05:55 PM - 3 Likes   #7
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Not only is this possible, but I've made the mod to my camera. It takes less than 5 minutes to do, and less than 5 minutes to undo - although so far I have found NO reason to undo it.

The 3rd pin from the left is indented so that it is only shorted when a A lens is in the A position. If you examine an A lens, you'll see the pin stick out in the A position, and retract when the aperture is set manually. You can try to cram a small wad of aluminum foil into the depression on the lens mount, but there is a better idea (not mine - I don't deserve the fame).

Remove all the screws holding the lens mount to the body. Lift straight off the body. Now cut a thin strip of aluminum foil about 6 inches (15cm) long - thin so you don't short the neighboring contacts. Fold the foil to about triple thickness - you need to be thick enough to fill the void and no more - so how many layers depends on the thickness of the foil.

Lay the strip over the contact with the extra to the outside of the mount (no excess on the optical (inside) of the mount). Carefully press the mount back into place - watch that the thin metal piece behind the mount is where it belongs. The mount will cut the foil sort of like a paper hole punch and the 'chad' should remain lodged in the mount hole on top of the contact pin. Put the screws back in place and snug them down. Tear the excess foil off from outside the mount.

Now your camera will think EVERY lens has an automatic aperture, AND that the lens is in the A position. Cool. Really cool. No more "F---" in your display. You will always see an aperture value displayed. But don't let this new found power fool you. You have also now acquired a new responsibility.

If your lens is not in or doesn't have an automatic aperture position ('A'), it is up to you to manually match the aperture your camera thinks it will be using with the actual aperture setting on the lens. You can do this by either adjusting the lens to match the camera, or by changing the camera so the displayed aperture matches the lens. Remember to always meter with the lens wide open. I went the next step and changed the green button function into a stop-down depth of field preview.

Some of us old farts really get into taking a 21st century computerized camera and turn it a 50+ year old match-needle wonder.
03-14-2012, 06:53 PM - 3 Likes   #8
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Do what JimJohnson said above: Here's a step by step photo series.


I think a piece of thin copper wire pulled from a lamp cord would work well as a substitute for the aluminum foil.

In use, I turn the ewheel f-number as low as it will go and manually preset the lens' aperture. The EXIF is wrong but the exposure is right because the camera doesn't try to close the aperture (I've told it to use the open aperture.)

03-14-2012, 06:59 PM   #9
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Thank you all so much for the great details and instructions.

I will trick my camera and give support soon. This hacker's way will make Pentax camera more fun
03-14-2012, 07:01 PM   #10
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Jim is correct and that will work, but you will still need to insulate the correct contacts on the lens so the camera knows what aperture wide open on your lens is.

Hans
03-14-2012, 07:26 PM   #11
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I forgot to mention that when the camera thinks the Lens is in "A" mode that P-TTL flash works. This is a great benefit and may be reason enough to fool the camera!
03-14-2012, 07:28 PM   #12
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QuoteOriginally posted by newarts Quote
I think a piece of thin copper wire pulled from a lamp cord would work well as a substitute for the aluminum foil.
I wouldn't try using copper wire. It is harder than the aluminum foil and may damage the lens mount when you press it back into place. The foil is easily cut forming the 'chad' within the contact hole on the lens mount.

I personally don't have a strictly manual lens to test. So my 'A' lens are always at full open until the lever is pressed. With the green button programming set to stop the lens down, I can see that the lens stops to its manual setting.
But if you have a strictly manual lens, you should be able to use either Av or M mode, set the aperature wide open during metering, then use the e-dial to adjust to the desired f/stop, lock exposure and finally set the lens' aperture to match what the camera says.

Regardless - fooling the camera into thinking all lens are using an automatic aperture harms nothing and allows you to see what the camera thinks is the aperture.
03-14-2012, 07:32 PM   #13
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I really love this thread. Great tips.
03-15-2012, 01:50 AM   #14
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with this trick all M lens will become A like
03-15-2012, 06:00 AM   #15
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Here is a link for altering the lens contacts and it's effect on metering

Hans

http://www.robertstech.com/matrix.htm
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