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Thread: Trouble with Computar lens and RJ Camera adapter

  1. #1
    thearne3
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    Trouble with Computar lens and RJ Camera adapter

    I have now collected a couple of Computar lenses (25mm and 12.5mm) and have made the unpleasant discovery that my RJ Camera C-mount adapter is not the same as the hawkpen adapter for my lenses.

    The first 'shoulder' on the lenses is 30mm (no problem). The second shoulder is ~38mm, which is easily filed down to 37.2mm. However the third shoulder is 39.2mm and, unlike the hawkpen adapter, there is no 39.2mm notch in the RJ Camera adapter, so this wider shoulder must be filed down to 37.2mm as well.

    I have only done the 25mm lens. I filed down the outer two shoulders so that all three shoulders add up to 3mm of total depth (measured from the base of the screw mount toward the front of the lens) with diameter less than 37.2mm. The lens appears to be fully seated, but still only focuses to about 5' max at f1.3.

    Has anyone been able to achieve infinity focus with this lens and the RJ Camera adapter?? Is the issue the lens, the adapter, or am I wrong and the lens isn't fully seated?

    Thanks for any insights...

    Tom

  2. #2
    Senior Member Y.B.Hudson III's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    Not a scientific reply..However, I have modified Computars, Navitars, Fujinon lenses to fit the Hawk II. I subsequently bought a RJ and found that none of my modifications worked on it... I'm not into self abuse, so I just use the RJ for lenses that don't require
    modifications. For what it's worth...I have a Xenplan 25 that works unmodified on the Hawk II, but doesn't fit the RJ.
    Last edited by Y.B.Hudson III; 5th September 2009 at 00:17.

  3. #3
    turbo
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    Re: Trouble with Computar lens and RJ Camera adapter

    The Computer 25/1.3 can be made to fit the RJ adapter, but requires a good bit of milling.

    http://forum.getdpi.com/forum/attach...1&d=1252876738


    When completely seated a couple of threads should extend beyond the end of the adapter.

    http://forum.getdpi.com/forum/attach...1&d=1252876738


    or buy the hawk.
    Last edited by turbo; 13th September 2009 at 14:03.

  4. #4
    echols
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    Re: Trouble with Computar lens and RJ Camera adapter

    Where can you buy the Hawkpen c mount adapter?
    thanks
    echols

  5. #5
    Senior Member pellicle's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    Hi

    Quote Originally Posted by echols View Post
    Where can you buy the Hawkpen c mount adapter?
    thanks
    echols
    eBay ... here is his profile.

    I use his adaptor with small modification to the computar ... search for my thread on that here :-)

  6. #6
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    Re: Trouble with Computar lens and RJ Camera adapter

    Although this is not exactly on topic, I have the Hawkpen C-mount (Bolex version) and Robot flange and an RJ Camera 4/3 to M4/3 adapter and OM to 4/3 adapter and must say the Hawkpen C-mount adapter is better made.

    The older 2-part adapter for the OM lenses does not align as well as it should but is adequate. I was thinking of getting the newer 1-part OM to M4/3 adapter but am not sure if the quality is as good as it should be based on the 2-part one.

    I am not into machining lenses so haven't bought any C-mount lenses. The grub screws used to hold and align the Robot flange on the Hawkpen adapter are so small that I would probably buy a second adapter rather than chancing breaking the heads of the screws.

  7. #7
    Senior Member pellicle's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    Hi

    Some time ago I put up a page here to address mounting issues on the Computar with the HawkPeng adaptor ... its a no go on the RJ adaptor without the sorts of lathing seen above

  8. #8
    MrAdrenalin
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    Re: Trouble with Computar lens and RJ Camera adapter

    Hi Y.B.Hudson III,

    Could you post some pictures and a guide for the modification of the navitar 75mm 1.3 to get infinity with the hawk adapter? Is there anything special you need to think about for the modification of the fujinon lenses (especially the 50mm 1.4)?

    Best regards,

    Magnus

  9. #9
    Senior Member Y.B.Hudson III's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    Magnus, no problem... off the grid today, I will post pics tomorrow...



    Hudson

  10. #10
    thearne3
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    Re: Trouble with Computar lens and RJ Camera adapter

    Thanks for the encouragement, Turbo, I now have both the 25mm and 12.5mm Computar lenses working with the RJ adapter - They even almost align vertically! However, still fine tuning infinity focus...

    BTW, I have been using a small three-sided file for the work - makes a very clean notch. Couldn't find anyone locally with a lathe - that would have been perfect!

    Happy hacking!

  11. #11
    turbo
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    Re: Trouble with Computar lens and RJ Camera adapter

    Quote Originally Posted by thearne3 View Post
    Thanks for the encouragement, Turbo, I now have both the 25mm and 12.5mm Computar lenses working with the RJ adapter - They even almost align vertically! However, still fine tuning infinity focus...

    BTW, I have been using a small three-sided file for the work - makes a very clean notch. Couldn't find anyone locally with a lathe - that would have been perfect!

    Happy hacking!

    What I did was build a pilot to center the base of the mount (removed from lens) in a drill press. Start the drill press to get the mount spinning and then use a dremel to grind away, stopping frequently to measure.

  12. #12
    MrAdrenalin
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    Re: Trouble with Computar lens and RJ Camera adapter

    Hi again Y.B.Hudson III,

    I guess you just been busy but still looking forward to the pictures.

    Best regards,
    Magnus

  13. #13
    Senior Member Y.B.Hudson III's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    Magnus, yehh trucks breaking down, cows calving, but "The pics" should be up be up by 15:00 GMT, thursday 24 September...

    regards, Hudson

  14. #14
    Senior Member Y.B.Hudson III's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    Navitar 75mm 1.3... for Hawk II adapter...




    1 unscrews, 2 lifts off...


    0.8mm ... finished dimension.







    on my example of this lens...it focused past infinity, I'll continue with how to adjust the lens for infinity collimation tomorrow...

  15. #15
    thearne3
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    Re: Trouble with Computar lens and RJ Camera adapter

    Hudson -

    Just a nudge...some of us are very interested in 'Part 2'! Your efforts are very much appreciated.

    Best,
    Tom

  16. #16
    Senior Member pellicle's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    yes, and your image story is quite compelling and well executed!

  17. #17
    Senior Member Y.B.Hudson III's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    yehh, thanks...will post part two in a couple days...I have some cowboy stuff to finish up first...




    regards, Hudson.

  18. #18
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    Re: Trouble with Computar lens and RJ Camera adapter

    ouch! That's the part I am thinking of and I dare not to do.

    I knew that, GF1 and EP-1 have no such a problem deal to the area in front of the sensor is larger. I used to think of open it wider but now I think I can skip it.

    Thanks so much, Hudson!

  19. #19
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    Re: Trouble with Computar lens and RJ Camera adapter

    I am trying to mount a Navitar 75mm 1.3 to c mount adapter for m4/3s. Does anyone know what has happened to the illustrative images and also the rest of this thread which seems to just end abruptly?

  20. #20
    Senior Member pellicle's Avatar
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    Re: Trouble with Computar lens and RJ Camera adapter

    Quote Originally Posted by turbines View Post
    Does anyone know what has happened to the illustrative images and also the rest of this thread which seems to just end abruptly?
    not exactly, but if you don't yet have an adaptor then I suggest the hawkpeng one.

    fits nicely ... reference the blog post I put up on one of the earlier posts on this thread to see.

  21. #21
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    Re: Trouble with Computar lens and RJ Camera adapter

    Thanks!

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