Adapting a lens that has no focus?

Discussion in 'Beyond the Basics' started by Yan Lauzon, Oct 27, 2018.

  1. petrochemist

    petrochemist TPF junkie!

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    I don't think I've ever seen one!

    Can you recessed your lens deeper into the helicoid? There are M42-M52 helicoids and even some at M65 IIRC.

    My 50/1.2 projector lens is mounted so the rear of the lens would have stuck out the back of the helicoid & adapter - there was some spare metal behind the last element that I've trimmed off so it's now roughly flush with the back at the helicoids shortest.


     
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  2. Yan Lauzon

    Yan Lauzon TPF Noob!

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    Recessing it inside the helicoid isn't something I considered yet. How do you attach it inside?
    The lens is thin and may fit within something not too wide. Maybe I can adapt the body to screw in the adapter directly?

    On another note, I found out a supposedly 10-13.5mm helicoid made by a company named pixco, but nowhere I see them available in Canada. I wonder if it's a US venders with a bad inch-cm conversion...
     
  3. petrochemist

    petrochemist TPF junkie!

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    It's the middle one of these three, with a stepping ring glued (hot melt) to the barrel about an inch back, where there happened to be a convenient ridge.
    [​IMG]3 projectors small by Mike Kanssen, on Flickr

    The other two both fit the same helicoid (a 35-90mm long M42-M52 model) via similar means.
     
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  4. Yan Lauzon

    Yan Lauzon TPF Noob!

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    I'll take some measurements and shop yet again for parts...

    Sticking a stepping ring isn't a bad option if it fits. Thanks for the idea.
     
  5. petrochemist

    petrochemist TPF junkie!

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    I like to keep a good stock of different sizes available for things like this (as well as for filters). There are an amazing variety of them available, many at nice low prices, if you can wait a few weeks. If required a little tape underneath or a little gentle sanding can sometimes adjust the fit of one that's not ideal. Nothing complicated needed, its the adapters that go behind the lens that get tricky to jury rig.
     
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  6. Yan Lauzon

    Yan Lauzon TPF Noob!

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    Trying things with my lens today... The way it is built wont adapt well to a m52. The whole thing is a bit less than 60mm diameter. If I stick it to a m65, it will have to be on the aperture ring, so I'd ave to turn the whole lens from the tip for aperture. I still don't know how I'd make it hold in place.

    I tried to open the lens in case I could change some properties, but it's been tampered with in the past and one screw is broken in place, so that won't happen

    I got into thinking... 10mm isn't huge. I almost get there with just unscrewing the m42 adapter.

    Maybe all I need is a m42 macro extension ring
     
    Last edited: Dec 16, 2018
  7. Yan Lauzon

    Yan Lauzon TPF Noob!

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    In case anyone is curious...

    I did find a set of m42 focus adapter ring set (and a cheap one at that) that had a thin enough ring, and gave it a try. Works to get focus. Not easy by any means but does work rather well.

    I'd still prefer a thinner helicoid... But the one I managed to see with interestingly low thickness specs was just uneconomical, so unless I get a good deal, the focus adapter ring will have to do.

    This lens is rather sharp given the correct circumstances!
     
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