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Thread: Centre filters for UWA lens - rear element instead of front

  1. #1

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    Centre filters for UWA lens - rear element instead of front

    This might sound like a ridiculous idea, but I'm wondering why can't centre filters be made for the rear elements? Lenses like the Super Symmar XL 110mm has a 52mm thread on the rear vs 67mm on the front, thus a centre filter on the rear will be smaller and less expensive to make?

  2. #2

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    Re: Centre filters for UWA lens - rear element instead of front

    Except the fall off already occurred when the light rays pass through the rear element. Also, placing a filter behind the lens creates a focus shift = 1/3rd the thickness of the filter material.

  3. #3

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    Re: Centre filters for UWA lens - rear element instead of front

    Quote Originally Posted by Bob Salomon View Post
    Except the fall off already occurred when the light rays pass through the rear element.
    A center ND doesn't stop falloff from occurring, it just darkens the middle to even out the exposure. It should have the same effect regardless of which end of the lens it's installed on.
    Trevor

  4. #4
    lenicolas's Avatar
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    Re: Centre filters for UWA lens - rear element instead of front

    Main problem I can think of is darkened image to compose and focus. But if you’re using a zone focusing camera then why not.
    "I am a reflection photographing other reflections within a reflection. To photograph reality is to photograph nothing." Duane Michals

  5. #5
    Alan Klein's Avatar
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    Re: Centre filters for UWA lens - rear element instead of front

    Quote Originally Posted by lenicolas View Post
    Main problem I can think of is darkened image to compose and focus. But if you’re using a zone focusing camera then why not.
    What's a zone focusing camera?

  6. #6
    Drew Wiley
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    Re: Centre filters for UWA lens - rear element instead of front

    For one thing, they're bigger than the lens diameter, and might not fit inside some bellows. They need to be made oversized to prevent vignetting. That's a hard place to install and remove it without risking resetting focus, especially since ultrawides tend to have both significant falloff and finicky focus, being so close to the film plane - yet another issue - it might make the lens too close to the film. Then you've got the cost factor - how many people would want one?
    You could have one custom made, no doubt, for an absurd sum. No need to go into the optical engineering issues relative to the intended task; maybe somebody else will pounce on that. Rear filters in general work poorly unless the lens itself is specifically designed for them in advance.

  7. #7
    lenicolas's Avatar
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    Re: Centre filters for UWA lens - rear element instead of front

    Quote Originally Posted by Alan Klein View Post
    What's a zone focusing camera?
    A camera that has no ground glass, prism, rangefinder or any other focusing system besides a distance scale on the lens.
    You estimate (or mesure with tape or laser) the subject distance and set the focusing accordingly.
    Click image for larger version. 

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    Panoramic 617 and 612 cameras are a good example of zone focusing cameras that use LF lenses on helicoid mounts.
    With mine I used to leave the center filter on all the time since you never look through the lens.
    "I am a reflection photographing other reflections within a reflection. To photograph reality is to photograph nothing." Duane Michals

  8. #8
    Drew Wiley
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    Re: Centre filters for UWA lens - rear element instead of front

    Just like rangefinders; you aren't looking through the lens when focussing. I made the mistake of forgetting to even remove the lenscap on my "Texas Leica" 6x9 in one instance a few days ago. Certain Technical cameras, like the Technika series, offered optional rangefinder focus as well as primary groundglass focus.

  9. #9
    Alan Klein's Avatar
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    Re: Centre filters for UWA lens - rear element instead of front

    Oh, so my Nikonos underwater camera was one of those too. You had to guess focus.

  10. #10
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    Re: Centre filters for UWA lens - rear element instead of front

    That Technorama is a scale-focusing camera. Zone focusing is the technique of using depth-of-field calculations, tables, or markings on the lens to set the distance so as to achieve good-enough focus across a particular distance range of interest. Zone focusing is a technique commonly used with scale-focusing cameras, but of course it can be used with any camera/lens combination that has a means of manually setting a particular focus distance.

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