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Thread: Focus Issue around edges

  1. #1

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    Focus Issue around edges

    Hey all, I wanted to share this photo of a cemetery and hope I could get a diagnosis. As you can see the edges are horribly blurry, even when shot pretty stopped down.
    All of my images using this seem to be like this. It appears the same in the ground glass as well, so maybe this is a lens issue? I only own this one lens, so I haven't tested the camera out with something else. This is my first time using a field camera, but monorail cameras in the field never gave me this issue.

    Lens: Nikkor-W 180mm f/5.6
    Shooting aperture: f/45
    Focus: Infinity
    Camera: Wista 45SP
    Movements: Front tilt, seemed to work to get the grass in focus.

    Click image for larger version. 

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    I have also attached a photo of some Dala horses so you can see how the lens behaves when shot wide open.
    No movements here:

    Click image for larger version. 

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  2. #2

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    Re: Focus Issue around edges

    A couple of possible issues: One, if the camera's focussing screen is not original - it may have been replaced incorrectly... with a front-mounted separate fresnel lens without a proper re-positioning of the actual ground glass. There is a formula for this and when I purchased a separate fresnel from Bill Maxwell for my 5x7 he shared this formula with me so I could make my own adjustment. At any rate...this possibility, combined with a possible field curvature of your Nikkor lens (many lenses have very slightly (or more pronounced) curved fields), might conspire to give you the result you show...where the now incorrect focus plane would still allow a small area of "focus" when the lens is stopped down...due to its field curvature. Then again...the wide open result looks too similar to be fully explained by this. Hmmm...perhaps your lens' elements are out of proper position? I once was given a "defective" enlarging lens to mess with...and discovered that one of its elements had been installed
    backwards! Probably a DIY repair gone wrong or accompanied by mind-altering substances.

    Or...maybe you have a combination fresnel/groundglass which is plastic, and you are putting enough pressure on this with your focussing loupe and this is deforming the screen slightly? This actually happened to me when I briefly owned a Linhof Technikardan - which has (IMHO) a lethal design flaw in that the supplied plastic fresnel/screen is (or was, if Linhof has since corrected this) supported by four relatively small plates, and not by the proper recessed shelf which would support the entire perimeter. (why, oh why, did LINHOF do this?) At any rate...I found that only sight pressure with my focus loop was deflecting the screen!

    Or...perhaps one of your lens cells has gotten a bit loose?

  3. #3

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    Re: Focus Issue around edges

    A Nikkor W should not have appreciable curvature of field. Nor should it be fuzzy around the outside of the image, especially when you are using no movements that really move the sides of the image out of the image circle that much. If I were you, I'd check to make sure all my lens elements were in tightly and that everything is screwed tight to the shutter. Test by shooting a planar surface (sheet of newsprint is good) with the camera zeroed and the the back parallel to the subject plane. Shoot at a wide aperture to minimize depth of field and see if you still have out-of-focus edges. If so, I'd suspect a problem with the lens.

    Best,

    Doremus

  4. #4
    Jim Jones's Avatar
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    Re: Focus Issue around edges

    Check that the shutter is properly mounted to the lens board, the lens board is seated in its frame, and the front standard is parallel to the film plane. However, f/45 should have reduced that problem. Doremus' suggested test, or shooting a textured wall, is a good idea.

  5. #5

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    Re: Focus Issue around edges

    Thank you guys, I will develop a couple more test shots today. Here are two photos of what it looks like in the ground glass, with the aperture wide open at f/5.6.

    John Layton, you are correct when you suspected that I have a plastic fresnel/ground glass combo. I've removed it, flipped it around, upside down, even pressed on it a bit, etc, but still get the same results, so I suspect that it's a lens issue.

    I have one shot dead on with everything zeroed, and one shot with front rise. As you can see in the latter, the focus is no longer at dead center when rise is applied, but at above dead center. I hope this helps.

    Click image for larger version. 

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  6. #6

    Join Date
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    Re: Focus Issue around edges

    Quote Originally Posted by John Layton View Post
    A couple of possible issues: One, if the camera's focussing screen is not original - it may have been replaced incorrectly... with a front-mounted separate fresnel lens without a proper re-positioning of the actual ground glass. There is a formula for this and when I purchased a separate fresnel from Bill Maxwell for my 5x7 he shared this formula with me so I could make my own adjustment. At any rate...this possibility, combined with a possible field curvature of your Nikkor lens (many lenses have very slightly (or more pronounced) curved fields), might conspire to give you the result you show...where the now incorrect focus plane would still allow a small area of "focus" when the lens is stopped down...due to its field curvature. Then again...the wide open result looks too similar to be fully explained by this. Hmmm...perhaps your lens' elements are out of proper position? I once was given a "defective" enlarging lens to mess with...and discovered that one of its elements had been installed
    backwards! Probably a DIY repair gone wrong or accompanied by mind-altering substances.

    Or...maybe you have a combination fresnel/groundglass which is plastic, and you are putting enough pressure on this with your focussing loupe and this is deforming the screen slightly? This actually happened to me when I briefly owned a Linhof Technikardan - which has (IMHO) a lethal design flaw in that the supplied plastic fresnel/screen is (or was, if Linhof has since corrected this) supported by four relatively small plates, and not by the proper recessed shelf which would support the entire perimeter. (why, oh why, did LINHOF do this?) At any rate...I found that only sight pressure with my focus loop was deflecting the screen!

    Or...perhaps one of your lens cells has gotten a bit loose?
    Linhof never supplied a plastic Focusing screen on new cameras. All Linhof cameras ever made came with a glass groundglass.

    You probably purchased a used camera that had the original ground glass replaced by someone with a Linhof Super Screen. These were never sold or used by the factory and was an optional add on that was only available in the USA and Canada and was sold under that name only because Linhof gave permission to use that name. The screen, and other similar ones like the Beattie, were manufactured in Rochester, NY by Fresnel Optics, the parent company of Beattie.
    Since the screen developed the possibility of sagging Fresnel Optics kept changing the composition of the screen but they were never able to totally eliminate in so it was discontinued. It would not sag if a long shim like a matchstick was placed under the Super Screen on either long side of the screen. If one had added the Grid Overlay, which was made from float glass, to the top of the Super Screen then the pressure of the loupe could not make it sag.

  7. #7

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    Re: Focus Issue around edges

    Alex,

    There appears to be something wrong with your lens. Do you have other lenses? If so, mount one and see if you have a similar problem.

    About your lens: Is it new to you? Have you shot with it successfully without this problem? Has it been damaged (e.g., dropped) recently? Have you had the lens repaired/disassembled recently (maybe incorrectly reassembled)?

    I can't really imagine how this could be a camera problem.

    Doremus

  8. #8
    IanG's Avatar
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    Re: Focus Issue around edges

    Wista used their own combo screen fresnel and ground side it's plastic on my 45DX and excellent, very bright ad accurate..

    Have you used the same lens on your monorail camera and is it OK, if not try it and if it's OK that eliminates it being a lens issue and should be the first thing you test. It's also possible someone's fitted the wrong screen to your Wista.

    With the first image I'd question why you focussed at Infinity, that's not good practice.

    Ian

  9. #9
    Thalmees's Avatar
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    Re: Focus Issue around edges

    Quote Originally Posted by Doremus Scudder View Post
    Alex,
    There appears to be something wrong with your lens. Do you have other lenses? If so, mount one and see if you have a similar problem.
    About your lens: Is it new to you? Have you shot with it successfully without this problem? Has it been damaged (e.g., dropped) recently? Have you had the lens repaired/disassembled recently (maybe incorrectly reassembled)?
    I can't really imagine how this could be a camera problem.
    Doremus
    +1
    Do you check if the lens originally has some washers between cell/shutter, and maybe missed?. Or the opposite scenario?
    Is the shutter(aperture diaphragm) working properly? I mean during exposure?
    Is it assembled on the correct shutter?
    Scanned photos still may corrected before downloading.
    Good luck Alex.

    The generosity of spirit in this forum is great, its warmly appreciated.
    ------------------------------

  10. #10

    Join Date
    Sep 1998
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    10,313

    Re: Focus Issue around edges

    Your lens is diffraction limited at f22. Have you tested it at 22?

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