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Thread: Modifying a Navitar 75/1.3?

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    Modifying a Navitar 75/1.3?

    I got one of these Navitar clones (at least I think it is the same lens as the Navitar 75/1.3), an Astroscope 75/1.4. The rear end of the lens looks like this:


    And here it is with a c-mount adapter:

    As we can see there is too much of the lens sticking out from the back side of the adapter. That prevents not only proper mounting (the lens can't be screwed into the adapter and mounted without hitting the light baffles in the G1) but also focusing to infinity.

    Now infinity is not of the greatest concern but I would like to try the lens in real use.

    Are there any Navitar, or Astroscope, experts here? How do I proceed?
    I could just cover the rear lens element and remel it down but I figure there is a better way to do it...

    regards,

    Jonas

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    Re: Modifying a Navitar 75/1.3?

    Y.B. Hudson illustrates clearly, step by step, how that can be accomplished, here:

    http://forum.getdpi.com/forum/showthread.php?t=9970

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    Re: Modifying a Navitar 75/1.3?

    The rear element on mine sticks out only a little less than your lens when fully extended (focus ring at infinity marking) and it adapts fine for me. Maximum focus distance for mine is at least 50m.

    Attachment 31252

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    Re: Modifying a Navitar 75/1.3?

    Quote Originally Posted by Vivek View Post
    Y.B. Hudson illustrates clearly, step by step, how that can be accomplished, here:

    http://forum.getdpi.com/forum/showthread.php?t=9970
    Thank you Vivek. I did search... OK, a file then.

    Quote Originally Posted by edz View Post
    The rear element on mine sticks out only a little less than your lens when fully extended (focus ring at infinity marking) and it adapts fine for me. Maximum focus distance for mine is at least 50m.
    Maybe there are some small differences between these lenses. Or they are the same. Hmm. I use a G1, maybe the baffles in the camera are different on your camera?
    50m sounds good.

    regards,

    Jonas

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    Re: Modifying a Navitar 75/1.3?

    Jonas, I did mine slightly differently. I just filed around the tip of the lens so that it gets into the baffle slightly and achieves infinity. No, it did not hit the shutter.

    Anyway, you do need to file away..

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    Re: Modifying a Navitar 75/1.3?

    OK, done.

    Thank yous go out to Vivek and Y.B.Hudson.III

    I'm lazy so I just taped it all carefully and dremeled away what didn't need to be there. Well, I left about 0.3mm of the rim around the rear lens element.

    I'm not only lazy, but also sloppy; when cleaning the kitchen I used the vacuum cleaner and whoops, there the stop screw for the adapter was lost. As a result I now have a nice 75/1.4 or 1.3 lens (who knows what they all really are) mounting properly and being able to focus to about 15-20 meters wide open.

    My first impression of the lens is that it is really good.

    Thanks again,

    Jonas

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    Re: Modifying a Navitar 75/1.3?

    I have a G1 too - I guess mine must have been almost touching the baffle. I decided to have a go at modifying it anyway. I unscrewed the back element and filed a little around the outside rim at an angle like Vivek suggested (I just used a nailfile for this). Lens focuses to infinity now, and I aligned the mount while I was at it.

    Is it worth painting the surface that was filed away black again? I was thinking that there might be a detrimental effect caused by more internal reflections - but then again the rear lens mount surface next to it is reflective anyway.

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    Re: Modifying a Navitar 75/1.3?

    Jonas, Congrats! Find a good length 58mm hood for it, shoot away and show some pics from it.

    EDZ, Yes, both the stainless steel mount and the filed away rear are best painted black so that the sensor does not see any shiny areas at all. You will notice a marginal improvement in the contrast on the LCD/EVF after doing this but it has a big (+ve) impact on the final full sized images.

    The c-mount lenses i (most) use now are semi-permanently fixed to their c-mount adapters and everything is light-proofed and reflection proofed.

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