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06-22-2022, 10:59 PM   #1
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Adding SDM pins to a teleconverter

Hi all,

I had a shower thought today that I might go forward and explore for myself. If you have any thoughts on the matter (or experience) please share it!

My thinking goes like this:
There are plentiful and cheap teleconverters available in k mount that are only KAF. These teleconverters have all the data pins of the current iteration of the k mount as well as the screw drive socket for F and Fa series lenses. What they lack are the power zoom / SDM contact pads of the later KAF2 mount. Because of this, such teleconverters are unable to drive autofocus on lenses that rely on lens based af motors.

Could an adequately motivated person add the SDM pins to one of these KAF teleconverters to create a homebrew KAF2 version?

I was planning on giving it a shot and making a proof of concept prototype with my Sigma 1.4x DG using sugru, soldering wire, and patience.

Any thoughts?


Last edited by Gerbermiester; 06-22-2022 at 11:05 PM.
06-23-2022, 12:28 AM   #2
pid
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i think it is more than the pure physical contacts. I think there it needs a little piece of software to work fast and properly. You can see the difference between the original HD 1.4x Converter which works fast and precise and the old Tamron AF- 1.4x Tele Converter which has the contacts and is also working with SDM lenses but very slow and uncertain. For me it indicates, that there is some software needed to work as expected. But give it a try!
06-23-2022, 12:29 AM   #3
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Not sure of the "plentiful supply" of suitable cheap teleconverters … maybe they're more widely available in your area than here
This application is likely to be relatively high current, so the actual electrical contacts will need to be of good quality, probably gold plated and the interconnecting wires not too thin.
After that it's just a simple case of precision engineering
Sugru would seem to not be an ideal choice of material, being apparently flexible, I'd be more inclined to make parts from a rigid plastic then glue these into place with a strong adhesive.
Good luck
06-23-2022, 06:35 AM   #4
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QuoteOriginally posted by Gerbermiester Quote
Hi all,

I had a shower thought today that I might go forward and explore for myself. If you have any thoughts on the matter (or experience) please share it!

My thinking goes like this:
There are plentiful and cheap teleconverters available in k mount that are only KAF. These teleconverters have all the data pins of the current iteration of the k mount as well as the screw drive socket for F and Fa series lenses. What they lack are the power zoom / SDM contact pads of the later KAF2 mount. Because of this, such teleconverters are unable to drive autofocus on lenses that rely on lens based af motors.

Could an adequately motivated person add the SDM pins to one of these KAF teleconverters to create a homebrew KAF2 version?

I was planning on giving it a shot and making a proof of concept prototype with my Sigma 1.4x DG using sugru, soldering wire, and patience.

Any thoughts?
Usually the thoughts I have under the shower disappear down the drain. I always look down and see one after the other good ideas take their way to the world . On the other hand, interesting idea, I like the thought and think of how much time and trial and error is involved and is it economically beneficial to do so. Or should I just buy the teleconverter that has all those possibilities on board and will deliver good instead of cheap looking results. I would do this only with a high quality teleconverter to get the best results. Thank you for sharing your idea!

06-23-2022, 09:36 AM   #5
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It would help to know which lens or lenses you have in mind to use with this wondrous new converter. Something like a 200/2.8 prime would work well, a 70-300/4-5.6 zoom not so much. You will be losing one stop of light and contrast and the AF sensor in the body needs everything it can get. Speaking of bodies, which one did you have in mind? I would not use a new K3 III for this sort of work...
06-23-2022, 10:53 AM   #6
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Thanks for the input so far!

I've got three teleconverters of the KAF type that just keep on showing up with package deals for used equipment. The Sigma mentioned in the original post is pretty good and the only version I actually bought as a standalone purchase. (A whopping $20 Canadian).

I'll be playing with my unconverted da*300mm f/4 to test the results.

If there's success, I'll go ahead and cast a better copy out of resin.
06-23-2022, 11:43 AM   #7
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The pins in the mirror box are spring loaded to help prevent binding and to account for any differences in tolerances. How are you going to achieve this?

06-23-2022, 01:50 PM - 1 Like   #8
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QuoteOriginally posted by Gerbermiester Quote
Thanks for the input so far!

I've got three teleconverters of the KAF type that just keep on showing up with package deals for used equipment. The Sigma mentioned in the original post is pretty good and the only version I actually bought as a standalone purchase. (A whopping $20 Canadian).

I'll be playing with my unconverted da*300mm f/4 to test the results.

If there's success, I'll go ahead and cast a better copy out of resin.
beware of the sigma converter, it only works on lenses that have a recessed rear element, because its front element protrudes into the lens bore.

the lens bore at the mount needs to have an internal diameter of 35 mm and the rear element of th e lens needs to be recessed 15mm
06-23-2022, 02:54 PM   #9
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QuoteOriginally posted by Not a Number Quote
The pins in the mirror box are spring loaded to help prevent binding and to account for any differences in tolerances. How are you going to achieve this?
Good question. I don't know yet. Any ideas?
06-23-2022, 05:20 PM   #10
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I often find myself progressing the thought to the easiest option being selling the not needed and picking up the desired article. I have been able with patience to pick up the converters 1.5 and 2 with the pz contacts for $50 aud each. I couldn't possibly manufacture the contacts and insert them and be sure that they would work for that dollar value to me. Also I have enough challenge finding time to use the equipment without manufacturing bits that can be bought. And I am not you, so happy figuring it out and best of luck.😊
06-23-2022, 10:30 PM   #11
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QuoteOriginally posted by Joetitch Quote
I often find myself progressing the thought to the easiest option being selling the not needed and picking up the desired article. I have been able with patience to pick up the converters 1.5 and 2 with the pz contacts for $50 aud each. I couldn't possibly manufacture the contacts and insert them and be sure that they would work for that dollar value to me. Also I have enough challenge finding time to use the equipment without manufacturing bits that can be bought. And I am not you, so happy figuring it out and best of luck.😊
Thanks!
This is just for a lark.
Success is unlikely, but I'll see how it goes.
6 Days Ago - 1 Like   #12
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Ok I'll play the game a little.
Look at the camera database and find out which of the mz series has the pz pins. The mz are notorious for breaking down and being sold for parts, even given away. This should give the pins with springs spaced correctly.
Your turn ☺️
6 Days Ago   #13
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QuoteOriginally posted by pid Quote
i think it is more than the pure physical contacts. I think there it needs a little piece of software to work fast and properly. You can see the difference between the original HD 1.4x Converter which works fast and precise and the old Tamron AF- 1.4x Tele Converter which has the contacts and is also working with SDM lenses but very slow and uncertain. For me it indicates, that there is some software needed to work as expected. But give it a try!
Having both convertors , I can confirm the same lens behaves different on the tamron. The pentax convertor provides the corrected focal length, the tamron not; and maybe other info needed for focus system. With the tamron focussing seems to need more iterations, maybe he needs the focal length to estimate the "throw" to the right focus point... maybe the lens provides some other info like x rotations of screw drive = y advance of focus and something similar for sdm, electric motors to assist body to determine focus.

Having the tamron acquired recently, I need more tests to make a better judgement...but the difference is obvious. But the sdm focus works, so electrical it's OK, but the control of focus is more hesitating...
6 Days Ago   #14
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QuoteOriginally posted by Joetitch Quote
Ok I'll play the game a little.
Look at the camera database and find out which of the mz series has the pz pins. The mz are notorious for breaking down and being sold for parts, even given away. This should give the pins with springs spaced correctly.
Your turn ☺️
That's really quite clever! I'll have to do some scrounging.
6 Days Ago   #15
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QuoteOriginally posted by mlag Quote
Having both convertors , I can confirm the same lens behaves different on the tamron. The pentax convertor provides the corrected focal length, the tamron not; and maybe other info needed for focus system. With the tamron focussing seems to need more iterations, maybe he needs the focal length to estimate the "throw" to the right focus point... maybe the lens provides some other info like x rotations of screw drive = y advance of focus and something similar for sdm, electric motors to assist body to determine focus.

Having the tamron acquired recently, I need more tests to make a better judgement...but the difference is obvious. But the sdm focus works, so electrical it's OK, but the control of focus is more hesitating...
It might be due to quality of electrical connection reducing current flow??? Who volunteers to pull their da 1.4 apart to find out😁
After thinking about it I would think that the data pins have the chip to correct FL and focus action and the pz contacts are "dumb".

Last edited by Joetitch; 5 Days Ago at 01:42 AM.
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