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  1. #1

    Tired of my ground glass

    Many years ago I broke the gg in my 5x7 camera. Too much wind, not enough weight. I tried making a new one using many different grits and types of grit. Whenever I got one that was really sharp and bright, I could see the iris as a bright spot. So I gave up and bought one from a reputable camera manufacturer which was fine, not too sharp, pretty even image as gg’s go so I lived with it. But. Now I would like to change it having used my 4x5 for a time and realizing that the image is Much sharper and even. It happens to have an old Bill Maxwell screen so I contacted Bill to see if he could also make a similar screen for my 5x7. He told me that he had changed his screen quite a bit and that it was much brighter but the angle of view from behind the camera was very narrow. I asked him if he could make one of the older style screens for me and that he would send me a quote. That was several months ago and several emails ago so I assume that he has either stopped making screens or doesn’t want to make the older version.
    Any ideas for a new screen that would be sharp and even over a large range of lens focal lengths?
    Thanks

  2. #2
    Maris Rusis's Avatar
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    Re: Tired of my ground glass

    Ground glass screens are a compromise. Optical law has not been repealed.

    The finer the grind the better small details can be focussed. But too fine and the screen tends toward transparency and a hot spot corresponding to the lens exit pupil appears. Focussing in the hot spot is good, elsewhere not so good.

    A ground glass gives an even picture when it has a high degree of scattering. But this means most light rays miss the observers eye so the screen is dim.

    A coarse ground screen can be brighter but fine detail focussing becomes ambiguous.

    A completely un-ground screen can be used for all lenses and apertures to provide bright aerial image focussing. But only in the direction of the lens exit pupil.

    A ground glass that incorporates a Fresnel element can redirect light rays that would otherwise miss the observers eye to deliver a brighter image. But the brightening is optimal only on the optical axis of the lens assuming the Fresnel is centred. The best effect is achieved when the focal length of the Fresnel is matched to the focal length of the imaging lens. The Fresnel pattern intrudes on the visibility of the finest detail and there is a brightness versus accuracy trade-off.

    The Maxwell screens are a famously good, albeit expensive, balance of the possibilities.
    Photography:first utterance. Sir John Herschel, 14 March 1839 at the Royal Society. "...Photography or the application of the Chemical rays of light to the purpose of pictorial representation,..".

  3. #3

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    Re: Tired of my ground glass

    Arca Swiss has a really excellent viewfinder experience, where they place the Fresnel lens between the ground glass and the lens. Normally, this will throw off the focus by a small amount. So, they offset the focus plane by the small amount that's needed to compensate for this shift.

    It would take some experimentation, but you might try replicating this configuration. It will improve the brightness and the evenness of what you will see in the viewfinder.

  4. #4

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    Re: Tired of my ground glass

    Barry Young on this forum makes focusing screens.
    https://www.largeformatphotography.i...Camera-Company

    Kumar

  5. #5
    Drew Wiley
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    Re: Tired of my ground glass

    I've found fresnels counterproductive and distracting. The right amount of grind on the glass will provide both comfortable viewing as well as allow acute focus under a magnifier. Very wide angle lenses with a lot of their own native illumination falloff will obviously be a challenge in terms of a potential "hot spot". Viewing with relatively long lenses is easier. And sometimes people are tempted to use a focus loupe just too high in magnification than you really need.

  6. #6
    Peter De Smidt's Avatar
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    Re: Tired of my ground glass

    Quote Originally Posted by Conrad . Marvin View Post
    Many years ago I broke the gg in my 5x7 camera. Too much wind, not enough weight. I tried making a new one using many different grits and types of grit. Whenever I got one that was really sharp and bright, I could see the iris as a bright spot. So I gave up and bought one from a reputable camera manufacturer which was fine, not too sharp, pretty even image as gg’s go so I lived with it. But. Now I would like to change it having used my 4x5 for a time and realizing that the image is Much sharper and even. It happens to have an old Bill Maxwell screen so I contacted Bill to see if he could also make a similar screen for my 5x7. He told me that he had changed his screen quite a bit and that it was much brighter but the angle of view from behind the camera was very narrow. I asked him if he could make one of the older style screens for me and that he would send me a quote. That was several months ago and several emails ago so I assume that he has either stopped making screens or doesn’t want to make the older version.
    Any ideas for a new screen that would be sharp and even over a large range of lens focal lengths?
    Thanks
    Bill works best via telephone. I'd give him a call. Set aside enough time, as the call is likely to last awhile.
    May tomorrow be a better day.

  7. #7

    Join Date
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    Re: Tired of my ground glass

    i replaced the gg in my speed graphic with frosted plastic film salvaged from a broken lcd monitor, sandwiched between the fresnel and plain glass. very fine grained and even illumination.

  8. #8

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    Re: Tired of my ground glass

    Regarding Maris's post I have often wondered if a Gg that consisted of an overall coarse grind and therefore an evenly spread bright image might not be combined with a central area of finer grind with its finer detail and brighter centre.

  9. #9

    Re: Tired of my ground glass

    Lots of really helpful information and ideas. Thanks! I will post again when and if I am successful or even if I decide to just use what I have.

  10. #10

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    Re: Tired of my ground glass


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