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Has anyone converted a lens before?

Forums Forums Get Technical Hardware Has anyone converted a lens before?

Viewing 6 posts - 1 through 6 (of 6 total)
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  • #1853
    orionid
    Participant

    So, I have one remaining lens from my old-school pentax days. It’s a Sigma 200mm Tele-macro with a Pentax K mount. The optics are in perfect condition, and It’s falling into the category where its value is higher than its worth. I’ve seen the same lens on the bay sell for $25-ish, but I can’t justify that in my mind. Not only did I learn to shoot with this lens, my dad took some amazing photos with it, including of the space shuttle Challenger. That being said, I’d like to keep and use it.

    Herein lies the problem. I switched to nikon with the purchase of my first dSLR in 2006.

    Nikons have a fairly deep focal plane, as does pentax, which makes it easy to adapt their lenses to shallower bodies. *glares at canon and micro 4/3’s users* But the reverse is almost impossible.

    Here are my ideas so far. I’d primarily (if not almost exlusively) use it as a dedicated macro, so I’m not concerned about losing infinity focus.

    1) Google-fu shows that there’s no plug-and-chug pk-nikon adapter commercially available. At least not from a reputable brand. The bay has cheap, chinese adapters with a lens element to allow infinite focus, ranging from $28-60. I’m not too keen on hoping for good optical quality out of a $30 lens.

    2) Find a cheap, possibly broken, sigma lens from the same (early 80’s) time-frame with a nikon mount, and change the mounts. My logic is that the manufacturers, in effort to save costs, would use as many interchangeable parts as possible, thus making the nikon mount on any lens the same as the nikon mount as any other, and any lens with multiple formats available to be the same lens with different mounts. I don’t know if this can/has been done, and google-fu doesn’t uncover much in this realm. Has anyone else tried anything like this?

    3) grab two sets of cheap, chinese extention tubes off the bay, at $10 per set, one with PK and one with Nikon. Swap the mount rings on one. As a side effect, there will still be two usable nikon tubes (which I could give to Kestrana, since I already have a set of Kenkos).

    Any experience in this realm would be greatly appreciated.

    #29206
    sleeping
    Participant

    Have you thought about buying the PK – Nikon adapter and removing the internal optical element? That would basically turn it into a very short extension tube. If you don’t want a lot of extension that might be the easiest thing to do?

    #29207
    ravnostic
    Participant

    Oh sure, I do this sort of thing all the time!

    *snort*.

    But really, if it’s anything like optics in telescope lenses (and really optics across the spectrum are the same in essence), then the #2 idea might lead to chromatic abberation, or focal diffusing (center focused, less so the further from center you go), or other aberations, which in themselves might actually be kinda cool, if unpredictable. The # three seems most viable to me, but stuff like this is well beyond stuff I’ve contemplated.

    But I’ll be following the thread to learn about it, and would be interested in what you decide to do and how it turns out.

    Thought: Buy the same lens on ebay for $25ish, and use that for your experiments, keeping sentiments regarding your dad’s lens safe and sound.

    #29208
    orionid
    Participant

    I did think about that briefly, but I don’t know if the diamater of the element’s mount is wide enough to prevent vignetting without the glass in place.

    #29209
    sleeping
    Participant

    Yeah, it looks like you’d need to remove that entire flange probably. Not sure if that could be removed in a reversible manner, but you could probably dremel/hacksaw it out.

    #29210
    orionid
    Participant

    So…….

    I got the fleabay adapter from hongkong. The lens elements were held in by a threaded ring that came right out. Initial tests were not so great, as the flange that held the lens elements caused an effective increase in f/stop without the bonus of a greater DoF. So I grabbed the dremel and widened it all the way out to the mounting ring. Now it works like a champ. The fleabay adapter was pretty solidly built, and I added a kenko 12mm extension tube to it today and took it out for a test drive. Initially, focus was extremely soft, at best. Then I popped the lens it up to f/11 and hooked up the flash, and I couldn’t be happier. Examples are in the gallery.

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