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Thread: measuring for filter thread

  1. #1

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    measuring for filter thread

    I have an older lens (Goerz Dogmar 16.5cm) that I'd like to figure out the filter thread for (and a couple of others as well.) I have a set of digital calipers so I can measure the diameter of the inside of the thread. Is that all there is to it, or do I need to account for the depth of the thread? If so is there a common depth that I can just add to the measurement? Sorry for the really simple question, but a search didn't find the actual filter size, or how to do the measurement reliably. Its around 40/41mm, and I don't have anything existing in that range to try screwing on.

  2. #2

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    Re: measuring for filter thread

    There’s a different approach that is often both easier and more correct: slip-on series filter adapter. Have you considered that? Measurement would be the OD of the front lens element

  3. #3
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    Re: measuring for filter thread

    Following on Brian’s suggestion, many old lenses don’t take screw in filters. The “threads” you see may be simply concentric grooves.
    Keith Pitman

  4. #4

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    Re: measuring for filter thread

    the OD of the front of the lens is 42mm. I assume they make slip-on to threaded adapters? How do the slip-ons "fit"? i.e. are they tight enough to support a square filter holder? Do they use rubber or cloth or something else to ensure a good grip? Aside from push-on LF lens caps, I have zero experience with push on filters.

  5. #5

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    Re: measuring for filter thread

    I feel kind of dumb, but it just occurred to me to measure a lens with a known filter size. The closest lens was a Nikkor-H 85mm ƒ1.8 F-mount lens. It should have a 52mm filter thread, and the digital calipers read 51mm, so it sounds like the thread is .5mm deep? I don't know if this is consistent across different sizes, but it seems likely. So, at least so far, it sounds like the trick is to measure then add 1mm.

  6. #6

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    Re: measuring for filter thread

    Quote Originally Posted by abruzzi View Post
    the OD of the front of the lens is 42mm. I assume they make slip-on to threaded adapters? How do the slip-ons "fit"? i.e. are they tight enough to support a square filter holder? Do they use rubber or cloth or something else to ensure a good grip? Aside from push-on LF lens caps, I have zero experience with push on filters.
    The series adapters are aluminum and grip the lens with “fingers”. I’d recommend a series 6 or 7 size. The adapter can be a mm or so oversized and the fingers can be bent to fit the lens.

    Best source of adapters, filters and shades is Tim Rice:

    https://filterfind.net/Series_7_A.html

    https://filterfind.net/series_6_A.html

    This is a series 6 adapter I’m using on a 1906 Kodak. You can see the “fingers”.

    Click image for larger version. 

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    Click image for larger version. 

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    Last edited by BrianShaw; 16-May-2021 at 22:28.

  7. #7

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    Re: measuring for filter thread

    The filters are unthreaded. They seat in the adapter and are locked in place with either a retaining ring or a shade.

  8. #8

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    Re: measuring for filter thread

    Here’s another example. This is an old Gundlach Radar that isn’t set up for screw-in filters. I couldn’t get exact fit so went about 2 mm larger and bent the tabs for a perfect fit. Kodak recommended +|- 1 mm of bending but, if careful, a bit more can be done without breaking tabs.

    Click image for larger version. 

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