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Thread: "Focus" problem that is driving me insane

  1. #1

    "Focus" problem that is driving me insane

    Hello,

    I have a problem that has been occurring for quite a while, which has been driving me crazy, and I believe is getting worse. Yet another shoot down the tube last week has me at at the end of my rope. I'm now questioning everything, my technique, camera, lenses, tripod, shooting environment, sanity. I'm hoping someone here might have a solution. Is the problem something I'm doing, or is it a technical issue?

    The problem I'm regularly having is that I'm getting part of the image coming out sharp, always the lower central part of the frame, then falling off to a blur in the upper area of the image. The unsharp part is not a soft out of focus lens blur, rather what looks to me like a motion blur.

    All the work is shot at night with long exposures, almost always at f32. The long exposures in itself shouldn't be an issue as I've had dozens of successes under nearly identical setup.

    Here's the most recent image. The white line indicates the border between sharp and unsharp.

    A detail of the sharp area:

    A sample of the problem:

    A closer view:


    As you should be able to see with the closer views of the problem, the blur is more of an overlapped or offset exposure as you'd expect with some sort of motion. However, if there were motion from ground vibration, wind, or from a tripod leg slipping, there shouldn't be a sharp area anywhere in the image. So I've ruled this out. (This image was taken on a still night with almost no traffic).

    Admittedly my perspective correction technique is self-taught from books, so this is where I have my largest suspicion. But I have had success with this technique. Here's my technique:
    - Set up and level the camera
    - ensure the lens is in the center of the vertical rise on the front standard.
    - frame the scene, which usually involves tilting the camera angle up (with the tripod head)
    - To correct the perspective I tilt the camera back forward till the grid lines on the ground glass line up with the structure
    - I then tilt the lens standard so it is perfectly parallel with the camera back.
    - Sometimes I then need to tilt the camera angle further up and repeat the standard tilts to get the scene framed correctly.
    - After focusing, the frame appears to be in focus throughout.
    - I then ensure everything is tightened down (and have been paying particular attention to this lately), and expose

    I would have expected that if there was a problem with my tilt adjustments not being perfectly parallel, that it would be compensated for with the stopped down lens (at f32), and any issues would appear as a soft lens blur. Again, I'm no expert in this. The problem I believe has also occurred in images without perspective adjustment. (Though I'm questioning my memory now too)

    I'm working with an Ebony 45RW, 135mm Rodenstock lens (used in the image), 90mm Rodenstock lens (which I'm having the same issues with), on an older Manfrotto Art 190 (silver) tripod.

    I can gladly post more problem images if needed.

    Thanks in advance for any help.
    William

  2. #2

    Re: "Focus" problem that is driving me insane

    I should add that this problem happens randomly. I'm still able to produce perfect night images, but 25-40% of the time now I'm having this problem.

  3. #3

    Re: "Focus" problem that is driving me insane

    Also, when the problem occurs, most of the time all of the images taken with the setup will have the problem. I always take a second exposure as a safety measure, and check focus in between.

  4. #4

    Join Date
    Apr 2009
    Location
    Seattle area, WA
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    864

    Re: "Focus" problem that is driving me insane

    Could be a film holder not loaded correctly or one is not holding the film flat Time to think about labelling your holders and recording which exposure goes to which holder. That way you can narrow down if it's a holder or not.

  5. #5

    Join Date
    Jun 2010
    Location
    Sussex, UK
    Posts
    126

    Re: "Focus" problem that is driving me insane

    Pinhole in the bellows? It certainly looks like motion blur or two images overlapping each other.

    Are you able to upload a full size image?

  6. #6
    Eric Biggerstaff
    Join Date
    Apr 2005
    Location
    Denver, Colorado
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    1,307

    Re: "Focus" problem that is driving me insane

    Film can "pop" during long exposures which can cause this, it sort of bows outward due to tempreture or humidity changes. I was just talking to a very well known photographer who is now doing a night project and he told me this just happened to him. The night was cool and foggy and he did not let the film adjust to the climate prior to exposure so it "popped" a little in the holder. Part of hte neg was sharp but a section of it was soft. Perhaps this is occuring.
    Eric Biggerstaff

    www.ericbiggerstaff.com

  7. #7

    Join Date
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    Re: "Focus" problem that is driving me insane

    I was going to guess a film pop too.

  8. #8
    Moderator
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    Re: "Focus" problem that is driving me insane

    Film pop #3. The tell-tale is that the exposure in the affected areas looks doubled-up, indicating that the film was sitting in one position for a while, and then in a different position for a while. I've had this happen to me very occasionally.

    Further to what Eric said, try pulling the darkslide and letting the film equilibrate to the prevailing temperature/humidity before you open the lens to make the exposure. You may need to experiment a bit to find out how long you need to wait for the film to "pre-pop".

  9. #9

    Join Date
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    Re: "Focus" problem that is driving me insane

    At f32 you are in diffraction. What happens at f22 or f16?

  10. #10
    Format Omnivore Brian C. Miller's Avatar
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    Everett, WA
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    Re: "Focus" problem that is driving me insane

    What is the exposure time? Are you using a cable release?

    I can only recommend that when you pull the dark slide, wait a minute for the film to settle down. That amount of time should allow the film to equalize with the air inside the camera. Also, give the holder a tap before putting it in the camera.

    Added:
    From looking at the areas which show the problem, it is definitely a motion problem. When the exposure starts, the film is in one position, and then it shifts to another position, in a diagonal upper-left to lower-right movement. Look at the upper-right side of the photo. Is the movement in the same direction, or a different direction, as if the film momentarily bowed in the middle?

    From the way you describe your procedure, it sounds like the camera does not have enough front rise for your photo. Is this correct? (This happens to me, too, I'm just trying to nail things down.) If there is enough front rise on the front standard, then just use that instead of tilting the camera back and adjusting the standards.
    Last edited by Brian C. Miller; 11-Jan-2011 at 17:48. Reason: more analysis

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