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Engineering an arpeture control M42 to micro four-thirds adapter

Discussion in 'Adapted Lenses' started by burdickjp, Mar 5, 2013.

  1. burdickjp

    burdickjp Mu-43 Veteran

    Feb 25, 2013
    So my wife is the shutter bug and in a quest to do more things together I decided to pick up a camera. Being an advocate of open standards, open source, and industry collaboration of course I was going to get something in the micro four-thirds form factor.
    So a few weeks ago I grabbed an Olympus PEN EP-2 from Amazon, body only, and a kit lens.
    Being an engineer at heart ( and pursuing such as a career ) I also picked up an M42 lens adapter and started hunting down manual lenses. I'm the kind of guy that prefers operations to come with trim adjustment knobs, and don't like things happening automatically when I can do them myself. I drive stick. I run Linux. Naturally I'd opt for manual lenses.

    While the selection of preset lenses isn't bad, I'd like to use some of the auto lenses, and while using them in a stop-down mode also isn't bad I don't see why an adapter can't be made which can push the aperture pin. I went looking for one, and couldn't find it, so please stop me if they do exist.

    So being the hacker I am, I pulled the lens mount off my EP-2 and threw it up on the optical comparator:
    Subscribe to see EXIF info for this image (if available)

    Subscribe to see EXIF info for this image (if available)

    I then dropped the coordinates into a least-square fit scipy module and had it spit out the closest circle. I plugged the coordinates into FreeCAD and am now close to having a model of the camera side of the interface.
    Subscribe to see EXIF info for this image (if available)

    Next will be the M42 mount ( easy, of course ) and then comes the fun part: the aperture control mechanism. I'm a rather busy student, so don't expect this to happen tomorrow, but I'm definitely having fun with my new camera!
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  2. Ulfric M Douglas

    Ulfric M Douglas Mu-43 Hall of Famer

    Mar 6, 2010
    Keep updating!
    Show some milling ...
  3. F1L1P

    F1L1P Mu-43 Veteran

    Jan 2, 2010

    btw. how "primitive" is that machine? It gives you width and height (silhouette) of the projected object and would be similar to placing camera mount on a regular flatbed scanner or does it give you complete " 3D scan" of the mount? :drinks:
  4. I don't want to stop you because what you're doing is very cool, but M42 adapters with an internal flange to depress the aperture pin do exist.

    Subscribe to see EXIF info for this image (if available)

    The one on the right with the flange is a $5 M42 to EF adapter stacked with an EF to m4/3 adpater. I assume that they would be available in a single M42 to m4/3 unit, but at the time I was using the lenses on both Micro 4/3 and Canon EOS bodies.
  5. burdickjp

    burdickjp Mu-43 Veteran

    Feb 25, 2013
    Yep. My novoflex has that flange. What I'm looking at is making it move which would in some ways emulate the functions of a preset lens.

    That piece of equipment at the top is called an optical comparator. The lens has an extremely short depth of field, meaning the shadow on the screen is only in focus for a distinct distance away from the lens. The digital read-out to the right is in millimeters, which means it reads to a thousandth of a millimeter, aka a micrometer, aka a MU-meter. This is VERY precise!
  6. HarryS

    HarryS Mu-43 Top Veteran

    Jun 23, 2012
    Midwest, USA
    Are you looking just to have a manual control on the aperture pin or did you want to have electrical control, allowing one to focus wide open and have the lens stop down for exposure?

    The latter is possible, but it would require reverse engineering the signal protocol between lens and camera. If I still had access to a logic analyzer, that would be fun (as we engineers/ex-engineers define fun) to figure out.
  7. burdickjp

    burdickjp Mu-43 Veteran

    Feb 25, 2013
    manual. Similar to what Novoflex has for some of their adapters, but oddly not for the M42 one...
  8. Ramsey

    Ramsey Mu-43 Top Veteran

    Jan 9, 2013
    Zagreb, Croatia
  9. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    Oh man, go all the way, go electrical.
  10. Stephen

    Stephen Mu-43 Regular

    Jan 2, 2013
    It would be quite feasible to have a M42 auto diaphragm on a 4/3 mount, the adaptor would have the release built in which also would close the diaphragm, and an electric switch fire the shutter. The switch could be a small micro switch unit inside the adaptor itself. This in appearance would be about the same as the Exakta external shutter release, but could be a lot neater.
    Some other bayonet auto diaphragms could be arranged in this manor.
  11. burdickjp

    burdickjp Mu-43 Veteran

    Feb 25, 2013
    Wow. I'm just looking to have a ring on the adapter which pushes the aperture pin when turned. Easy.
  12. burdickjp

    burdickjp Mu-43 Veteran

    Feb 25, 2013
    I got some more work done on this yesterday. I quickly came to the end of my understanding and patience for FreeCAD, so had to fire up my Windows 7 virtual machine and open Solidworks.

    I redid the work I'd done before and then started into my initial design for the actual stop-down actuator. I've already got something a liite different in mind, but this conveys the general idea of the assembly.
    Subscribe to see EXIF info for this image (if available)

    The helical grooves will be moved by pins which are located on a ring. Rotating the ring should move the actuator axially, thus actuating the stop down of the lens by depressing that curious little pin on the back.
    The straight grooves will contain two rubber rings. These should keep some friction in the assembly, which will prevent the actuator from moving around too much on it's own.

    Next on the list is the M42 threads, which may end up being the way the whole thing will be held together. Unfortunately, it's not as easy as one would think.
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