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"Strange" M42 mount question...

Discussion in 'Adapted Lenses' started by davehg, Jun 3, 2013.

  1. davehg

    davehg New to Mu-43

    7
    Jun 3, 2013
    Hello. I am hoping you can help me. I have been experimenting with adapted manual lenses. I just bought a Sigma XQ 28mm f2.8. It was sold with an M42 mount advertised. However, when it arrives there are some irregularities with the mount when compared to my Helios and Hanimex lenses. I posted photos showing the difference.

    1. Is this a M42? It does screw down to a certain point, but the square "pin" and blade (flange? - see the photos), means it will not screw down enough to actually depress the infinity-focus pin. I noticed this on another M42 on sale at ebay by the way, so any background information would be helpful to me and appreciated!

    2. If not what is it?

    The lens is in *MINT* shape, so I am loathe to give up on it. Any help would be appreciated!

    Thanks

    Dave
     

    Attached Files:

  2. davehg

    davehg New to Mu-43

    7
    Jun 3, 2013
    I just noticed there is a NEX forum so I did post there, but I imagine this could be an issue for any user of adapted lenses so I will keep the post open here as well.

    Again, any insight would be appreciated! Thanks!
     
  3. slothead

    slothead Mu-43 All-Pro

    Aug 14, 2012
    Frederick, MD
    I notice that in your last image you mention the lip that keeps the lens from being fully screwed. It appears to me that you ARE fully screwed. :biggrin: Good luck with it, I certainly can't help.
     
  4. KS11

    KS11 Mu-43 Veteran

    411
    Jan 31, 2011
    Busan/Hong Kong
    IIRC some manufacturers such as the rare and weird olympus m42 camera (before the om1) had a pin to make it a quasi m42 olympus proprietary mount. You can try to file those nubs down so they can work on your adapter.
     
  5. davehg

    davehg New to Mu-43

    7
    Jun 3, 2013
    Slothead: Well thanks for the honesty! I did smile. It's strange, for the NEX some M42 adapters appear to not have that lip, so I may not be just done in just yet. If I can get one without it, a bit of epoxy may well fix the issue! :D

    It's annoying, because My Helios 44M and my bargain-basement Hanimex 135mm are fine...it's just this one that is the problem child!
     
  6. davehg

    davehg New to Mu-43

    7
    Jun 3, 2013
    KS11: Thanks for the advice. It sounds rather scary to do that. It would take quite a bit of filing to get the larger protrusion filed down and the thought of the filings getting in the lens scares the hell out of me!
     
  7. KS11

    KS11 Mu-43 Veteran

    411
    Jan 31, 2011
    Busan/Hong Kong
    Before you hack it though, do those protrusions do anything? Auto or manual Aperture or whatnot? If not file away like there's no tomorrow....
     
  8. burdickjp

    burdickjp Mu-43 Veteran

    235
    Feb 25, 2013
    What about finding an M42 adapter which doesn't have that lip?
     
  9. davehg

    davehg New to Mu-43

    7
    Jun 3, 2013
    Not that I can determine. The small one definitely does not, and the larger one does not depress but as you move the aperture ring it does move. Also, there is not an auto/manual switch, but my Helios doesnt have one either.
     
  10. davehg

    davehg New to Mu-43

    7
    Jun 3, 2013
    I looks like I will need to grind/file them down. I found out I need the spring-load pin. I am pretty sure I have this figured out. The spring-load pin that compresses on the lip on the adapter allows the aperture to be controlled by the ring on the lens, and if not depressed the aperture stays wide open. I suspect the protrusions are for the camera body to control it, the smaller stationary one being a "stop", and some sort of motor rotating the larger to open/close it. That is pure conjecture but the only thing that makes sens to me.
     
  11. RobWatson

    RobWatson Mu-43 Hall of Famer

    If it were me I'd modify the adapter and leave the lens alone. Maybe even dedicate a modified adapter to the lens.
     
  12. Petrochemist

    Petrochemist Mu-43 Top Veteran

    651
    Mar 21, 2013
    N Essex, UK
    Mike
    I've never heard of an infinity focus pin on M42. I think you'll find its an auto aperture pin of which there were several designs.
    Most close down the aperture to the set size when the pin is pressed in, but keep it wide open if the pin is not pressed. A manual/auto switch on the lens often exists as well which disables this function.
     
  13. davehg

    davehg New to Mu-43

    7
    Jun 3, 2013
    Agreed. If you look at the later posts I did make the correction. I ended up taking out the dremel and grinding those protuding parts down flush. The lens seems to work when doing some quick tests. I do need to take it shooting. Then we shall see. I paid $40 for it including shipping, so if it is a fail, I am not all that concerned. I was just trying to score a cheap 28mm to play with. Sigma actually makes those 19mm and 28mm natives for NEX and M43, and I can score one of the remaining first gen models for around $150, or even less.
     
  14. dwig

    dwig Mu-43 Top Veteran

    621
    Jun 26, 2010
    Key West FL
    After years of only having stop down metering on their cameras, Pentax (then Asahi) added two tabs to rear of their lenses. One was a fixed index tab and the other was connected to the f/stop ring. The position of the f/stop tab relative to the index tab signaled the set f/stop to the body's meter. This coupling was used in the Spotmatic F, the ES, and the ES-II.

    When adapting the Asahi/Pentax Takumar brand m42 lenses, any version, you are best off choosing an adapter that does not have the plate that presses the stopdown pin. The lens's own A/M switch will provide the necessary function and allows full aperture viewing and focusing with a simple flip of the switch to close to the chosen shooting aperture. In effect, the lenses act as a "pre-set" lens rather than manual.

    Adapters with the plate to press the pin won't work with the Takumar lenses that have the extra tabs. I believe these lenses are all branded "SMC Takumar". There were very few third party lenses that offered these tabs for full aperture coupling with that last set of m42 Asahi Pentax bodies. If you encounter any and if they have their own A/M switch then you should use an adapter without the plate. If they lack the A/M switch then some modification is in order. Removing the tabs on the lens is one option.