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  1. #11
    oldnick's Avatar
    Join Date
    Jan 2009
    Medium Format
    Quote Originally Posted by ishutteratthethought View Post
    you may want to check to see if the screen is assembled correctly, i had a similar problem years ago with an acumatte so my camera guy reassembled the screen, he said the glass was "flipped" when ...aaahhemmm...someone cleaned it, after reassembly it worked great.
    Eheh, it could happen to anyone.

    But i don't have acumatte and have been able to focus no problem even bright sun light.

  2. #12

    Join Date
    Jul 2007
    Medium Format
    Are you sure the screen was not just put in the camera upside down?
    Disassembling the screen usually ends in tears, with the metal frame bent, and the thin glass cover broken.

    Anyway: an Acute Matte (D or not D) is only better than the old style screen in that it is brighter.
    In all other respects (including ease of use) an old screen is better.

    The thing that makes an Acute Matte are the many microscopically small pyramids that replace the ground glass surface.
    These screens are brighter, because these tiny structures direct light towards the eye (and that poses the question: where is your eye?), instead of scattering it in all directions (also away from your eye). (The way these thingies work is closely related to old 'cat's eyes' in roads, reflective coatings on traffic signs, and the reflective beads on projector screens).
    So far so good (except for the "where is your eye?" thing). Brighter is better, right?

    But there is a rub: these thingies work like tiny optical systems, which have a depth of focus. That means that there is no definite plane of focus, and your eye will be able to adjust for defocus, continuing to see the image in focus when you change the focussing setting. Only a little bit, but enough to make it hard to focus.
    The old screens too do not have a definite plane in which the image is seen. But its depth is limited to the difference between the highest peek and deepest trough of the corase ground glass surface. And that is far less than the depth of focus the Acute Matte screens produce.
    So to focus accurately, the old screens are better.

    Hasselblad also knew that, which is why they replaced the Acute Matte and introduced the D-version. The D-screens are a bit more like the old diffusing screens. But only a tiny bit.
    So they then changed the standard screen supplied with new cameras for one with a split image rangefinder.
    Split image rangefinders make very accurate focussing possible. So problem solved.

    But that's not the only problem Acute Matte screens have.
    They are also very sensitive to the position of your viewing eye. Not directly over the center, and not at the correct distance, and the screen will not appear evenly lit.
    Put a prism finder on the camera, and this problem too will go away. But without, you'll long back to days of the old screens.

    The nature in which the focussing screen image is produced by Acute Matte screens also changes how the out of focus bit look. And it is almost impossible to judge what you will get on film by looking at the Acute Matte focussing screen.
    Again, the old screens were much better.

    Not that the old screens are without their faults.
    They are, of course, not as bright.
    And the structure of the ground glass was rather coarse, and visible. The Fresnell lens of these screens is also much coarser, and more visible, than that of the Acute Matte's Fresnell lens.

    But still: given a decent amount of light, an old style screen is much better than an Acute Matte. Much easier to focus.

    Myself, i use Acute Matte screens.
    That's because my failing eyesight makes a split image rangefinder a must-have anyway. And i tend to have a prism on my camera too.
    But i don't mind using the old style (split image) screen at all.

  3. #13

    Join Date
    Jan 2009
    Los Angeles
    Multi Format
    I see said the blind man, so that's what happen to me a couple of weeks ago while using my 80mm, pics were out of focus. thought my lens was at fault but re shot again but focused with the split part and all was well , I was sweating it for a while,but relive after the second shot. Glad it wasn't a one time deal on the shot.


  4. #14

    Join Date
    Feb 2008
    Medium Format
    QG -

    Thanks for that fascinating explanation. I have the original style focus screen on my 500cm and have never felt the need to upgrade - focus is precise and easy.

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