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12-08-2020, 01:17 PM   #1
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Question for the Engineers: HSM non-Pentax to Pentax? More of a mind game

Recently I've been thinking, which is always a recipe for disaster, if it's possible to convert a non-Pentax HSM lens to K mount... Like Sigma's mount change service but on older, non-Global Vision lenses. The EX lineup. I also suppose that this has been discussed before.

Now, I'm talking about taking a lens manufactured by Sigma with an HSM module built in, like for Nikon, removing the mount, reworking the wiring to make it compatible with a Pentax KAF3 mount, adding shims to adjust for 1.04mm register difference, and mounting a KAF3 mount to it. Of course it would need to be reprogrammed to be usable on a Pentax camera but otherwise I think it's technically feasible.


Assuming Sigma manufactures their products to a high degree of interchangeability, with the major difference between the mount variations being the autofocusing module, rear barrel, lens mounts, programming, and lens adjustments to account for differing register, it seems rather doable on the surface. Practically very difficult but otherwise technically doable. What do you guys think? And I'm also not too sure that this is the best forum to post this but this is my best guess.

12-08-2020, 01:49 PM   #2
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It may be technically doable but is it worth the cost?

It is a big operation, so if it is made by a professional, it will be pricey.

The bigger issue is the electrical link: Sigma's contacts and Pentax's ones are not at the same place. Moreover, electrical voltage may be different.
12-08-2020, 02:20 PM   #3
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QuoteOriginally posted by MikeyBugs95 Quote
Like Sigma's mount change service but on older, non-Global Vision lenses. The EX lineup. I also suppose that this has been discussed before.
Sigma has offered mount exchange for the older models too, but the model must have been available in Pentax as well as the other mount. Sigma might be your best resource if you have a specific lens in mind.


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12-08-2020, 02:40 PM   #4
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QuoteOriginally posted by tryphon4 Quote
It may be technically doable but is it worth the cost?

It is a big operation, so if it is made by a professional, it will be pricey.

The bigger issue is the electrical link: Sigma's contacts and Pentax's ones are not at the same place. Moreover, electrical voltage may be different.

That's why it's mostly a thought experiment for me. I might actually try this with a cheap lens that I could pick up from eBay. About the link, true... It might be able to be remedied by using a Sigma Pentax mount HSM lens. But then another problem of screw hole alignments comes into play as well.


QuoteOriginally posted by stevebrot Quote
Sigma has offered mount exchange for the older models too, but the model must have been available in Pentax as well as the other mount. Sigma might be your best resource if you have a specific lens in mind.


Steve
Actually I do have a lens mind: the 300mm f2.8 EX. But I wouldn't be able to go through with this, or through Sigma, at the moment. The problem is that the Pentax lens is screw driven, it's one of the older APO EX/EX DG lenses so I don't think they'd add an HSM module to the lens. I also just spoke to a Sigma rep and they don't change mounts on these older EX DG APO lenses. They're not designed for it. They said it might be possible to do it personally but they don't it themselves.

That's why I'm going through this thought experiment of taking a Nikon mount lens with HSM and converting it over to Pentax including HSM, thinking that, all things being equal, it would might work because you'd be taking a lens that is produced in multiple mounts, already has the electronics in place and if it's truly meant for mass production, then the base of all the variants would be the same and should be possible to convert assuming you could acquire the spare KAF3 mount. Then all that would really be required would be to change over the rear barrel, if needed, and mount, rework the electronics and reprogram the lens. Ideally at least.


Last edited by MikeyBugs95; 12-08-2020 at 02:58 PM.
12-08-2020, 03:12 PM   #5
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Try Sigma lens mount service
12-08-2020, 03:14 PM   #6
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As an engineer, I CAN do almost anything like that. It would be more expensive for someone who was not Sigma to do it, since reverse engineering all of the control protocols would be the longest, most expensive part, and Sigma already knows all of that.

Most companies burden engineering cost at somewhere between $200 and $300 per hour. Say it would take 80 hours of engineering time for Sigma to do it, someone would have to buy ~ $20,000 worth of that service just to break even. If I did it, I'd want about 3X that many hours, so if you write me a $60,000 check, I would accomplish what you wish.

This answers the question why companies don't do things that seem like they would be easy to do; even small investments in manpower actually end up being very large outlays in money.

Last edited by Kozlok; 12-08-2020 at 03:20 PM.
12-08-2020, 03:28 PM   #7
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QuoteOriginally posted by rr1736 Quote
Try Sigma lens mount service
They only do that for the Global Vision lenses. Which the 300mm f2.8 EX is not.

QuoteOriginally posted by Kozlok Quote
As an engineer, I CAN do almost anything like that. It would be more expensive for someone who was not Sigma to do it, since reverse engineering all of the control protocols would be the longest, most expensive part, and Sigma already knows all of that.

Most companies burden engineering cost at somewhere between $200 and $300 per hour. Say it would take 80 hours of engineering time for Sigma to do it, someone would have to buy ~ $20,000 worth of that service just to break even. If I did it, I'd want about 3X that many hours, so if you write me a $60,000 check, I would accomplish what you wish.

This answers the question why companies don't do things that seem like they would be easy to do; even small investments in manpower actually end up being very large outlays in money.
Oh I know. Which is why I'd be thinking of doing it myself, if I do it. At least I don't have to pay myself.

12-08-2020, 03:35 PM   #8
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QuoteOriginally posted by MikeyBugs95 Quote

Oh I know. Which is why I'd be thinking of doing it myself, if I do it. At least I don't have to pay myself.
If anything comes of your Frankenstein project, Mike - let us know!
12-08-2020, 04:01 PM   #9
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QuoteOriginally posted by clackers Quote
If anything comes of your Frankenstein project, Mike - let us know!
What I'm thinking of doing is getting a cheapo Sigma HSM Nikon mount lens and trying it on there. Really the one thing I wouldn't be able to do is reprogram the lens to work on Pentax which admittedly is a huge problem. So obviously nothing would come out of it yet... But maybe someday.

But it brings up another question... How would I be able to read, and possibly, edit the lens' firmware?

Last edited by MikeyBugs95; 12-08-2020 at 04:08 PM.
12-08-2020, 04:01 PM   #10
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QuoteOriginally posted by clackers Quote
If anything comes of your Frankenstein project, Mike - let us know!
Think I would just pick up a lightly used Nikon.


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12-08-2020, 04:10 PM   #11
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QuoteOriginally posted by stevebrot Quote
Think I would just pick up a lightly used Nikon.


Steve
True... But I like a challenge. And tinkering.
12-08-2020, 05:23 PM   #12
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You lost me with thread title by saying, "More of Mind Game". I don't do well with those.
12-08-2020, 05:54 PM   #13
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Nice project, If you have the tools and patience, and of course a little knowledge. I think you can do this if you are confident. I'm looking forward to seeing the results.
12-08-2020, 11:39 PM   #14
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This is a hugely complex project because of the HSM and firmware. Even if you figure out how to interface with the lens electronics you won't know what firmware parameters need to be changed, or if the firmware has to be completely reprogrammed from scratch to accommodate Pentax communication protocols.

Someone did something related for Canon. It's not a mount swap, but a more limited firmware replacement that lets old Sigma lenses work with newer Canon bodies:
RECHIP - All About The Rechip

Martin Melchior's homepage: Conversion of an old Sigma lens to work with newer Canon bodies
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