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09-28-2012, 07:43 AM   #1
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Problem with Pentax 1.7x AF adapter

Hi there,

I just won the original 1.7x AF adapter from ebay, it can do AF with all K mount MF lenses on my K5, but it doesn't work with my T mount converted mirror, the AF does not function, it also does not mount my converted Leitz Summicron-R 50/F2 via K adatper, the mount does not fit, I know Leitz has at least 3 types of mount. Beside that, the other reason is all non working lenses have no aperture coupling level. I tried all camera settings but still no dice, I really hope to make my mirror work with the AF adapter, that is the reason I purchase it in the first place, I do casual wildlife shooting occasionally, can't afford any of those 'cannons', so a cheap and small mirror with AF adapter should fit the bill, any tricks ?

09-28-2012, 08:47 AM   #2
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Something just pop up on my mind, since the mirror is not like ordinary lens made with glasses, to compensate the effect of temperature on the metallic mirrors, the farthest focus point is 'over shoot' and go beyond infinity. So if I can find a super thin K to Kaf adapter, to fit in between the T to K mount and the camera, to make the mirror to mimic a standard AF lens, I might be able to regain AF via the said AF adapter, am I just dreaming ?
09-28-2012, 09:24 AM   #3
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Those small and cheap mirror lenses usually have a fixed aperture of f8.0. Place the F1.7x AFA behind the lens, the aperture value rises to f13.6. There is no AF system that will work at such dismal aperture. AF system's threshold seem to be about f6.3 if you go by the stated maximum aperture for the super zoom lenses at the telephoto focal length.
09-28-2012, 09:30 AM   #4
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Right, even my mirror is f6.3, the combination still won't work, but my f5.6 zoom did work.

09-28-2012, 09:32 AM   #5
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Most likely, your mirror lens is simply "too dark" (most are f/8) for the camera body's phase-detect autofocus to work at all, and adding the 1.7x in front of it will lower the amount of light even more.

I've actually had pretty good luck using live view on my K-5 and it's (slightly pokey) contrast-detect AF with the 1.7x AFA and my Tokina 500/8 mirror, but I had to pretty much nail focus beforehand and use the AFA to micro-adjust. Which camera are you using?

Also, do you have the camera body's custom function to "use aperture ring" set to "permitted?" Without this, any non-automatic aperture lens (Summicron, etc.) simply won't work on the camera as the meter has no idea what the lens is doing.
09-28-2012, 10:28 AM   #6
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After playing around with my 50mm SMC MF lens, which works perfectly with the AF adapter, I know I could make the mirror works with the adapter, by adding a pin somewhere on the T mount, to provide a fake f no. to the camera, but where to put it is the question. I wish there is one such T mount available somewhere but I couldn't find yet. For the converted Summicron, it just won't fit into the adapter, but fits fine directly to the camera I still don't know why.
09-28-2012, 10:57 AM   #7
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I have not looked at this in detail as my AF adaptor, which I have had since new in 1991, has never been used on a cheap mirror or on converted mount lenses, BUT

there are issues with later pentax gear not working as expected when used in conjunction with non conducting (painted or anodized) mounts. Case in point is vivitar auto extension tubes, they dont work on th eK5/7 unless you sand a patch to contact the pins on the camera.

I suspect you need to do something similar with your converted mount lenses.

but as others have said, even so, you will not get reliable autofocus with a combined aperture below F6.7 which means using an F4 or faster lens.

you may get some success with an F.56 lens but only on the latest cameras and only in bright light.,
09-28-2012, 12:32 PM   #8
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Yes I think you are right, there is definitely something to do with the electrical contacts.

I first tried to move the aperture coupling level by hand on the AF adapter and the camera, but only "--" shown on the LCD, not the expected f no., but when I fit a SMC MF lens to the camera and lock in 'A' mode, I can select aperture via the camera's thumb wheel, and the AF works. Then I compare the contacts on difference lenses, and check the conductivity with a DMM, I hope you can see my photo upload in here.

I only have 2 AF lens, let's count from CCW view from bottom. The 4th contact is missing but remains insulated on the telezoom, while the 6th contact also missing with exposed metal so it is short circuit to the camera. One the short zoom only the 6th contact missing and also short circuit.

Now on the 2 MF lens, the Samyang only has one contact on the 4th position, and it is short to chassis, and very slightly recessed from position1-3 so also will cause short circuit to the camera, 5th the same bare metal fully exposed, but 6th is insulated. On the SMC 50/f2 there is only one contact on the 5th position, and it is insulated only when NOT in 'A' mode, this is what makes the lens able to do AF with the adapter.

Now back to the T mount, it is painted so I assume non conductive, but should I sand the whole contacting surface, or just the 5th contact position ? it looks like short circuit won't hurt the camera, so I guess I will take the risk to shine it up and see what comes !

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09-28-2012, 12:41 PM   #9
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Yeah, you have to short the pins -- the lens has to have a conducting surface. You can just put foil tape on the T-mount lens. You can even use m42s with some foil tape.

Last edited by vonBaloney; 09-29-2012 at 09:51 AM.
09-29-2012, 03:56 AM   #10
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Yo need to short the pins on the K5 and K7. I don't know why Pentax changed this in their program, but earlier bodies did not care if it could not find a connected lens. I suspect it has to do with not wanting to move the aperture lever if it does not find a lens. But any way. The real contact to shor tis the 7th, thie data pin. This tells the camera nothing is connected. It may be they are also passing data through the other pins now, not just aperture coding.
09-29-2012, 07:11 PM   #11
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Two steps - first make your camera think all lenses are A-series-
https://www.pentaxforums.com/forums/pentax-k-r/178928-kr-short-contacts-chang...ml#post1867401

Second, short & insulate other contacts so the camera thinks there is a suitable aperture range-
http://www.robertstech.com/matrix.htm

For what it's worth, I use Magictape for insulators. I don't drill divots in my lenses as the above site suggests. This link shows pictures, scroll up a couple posts for the text instructions-
https://www.pentaxforums.com/forums/22-pentax-camera-field-accessories/113756-pk-extension-tubes-post1965895.html)
09-30-2012, 08:53 AM   #12
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I sand the whole contacting surface of the T adapter but didn't help to regain AF, after close inspection on the AF adapter, I found contact #4 is very slightly recessed, so I decided to stick a tiny piece of Tin foil on the T mount to short that contact, and yes that worked, I gain AF on my mirror now ! although it hunting around hardly stop right on the spot, at least I made it work, I will try on other brighter T monocular later.
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