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Thread: "Focus" problem that is driving me insane

  1. #11
    Octogenarian
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    Re: "Focus" problem that is driving me insane

    Have you tried mounting your camera on a heavier, more solid tripod?

  2. #12
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    Re: "Focus" problem that is driving me insane

    I don't see how this problem could be:

    1. Diffraction.
    2. Unstable tripod.
    3. Camera shake.
    4. Above, caused by cable release.

    All of these would affect the image with a different-looking pattern. A corkscrew motion of the camera might affect one end of the negative more than the other, but I do not see how such vibration could caused the double images. And given that the sharp end of the negative is at the bottom of the picture, which is at the top of the negative in the camera, the tripod-end of the camera would have to be wiggling back and forth with the top remaining still--the center of rotation would have to be near the top of the camera. I can think of no vibration mode that could cause that. And that sort of a shift seems to eliminate the possibility of the camera flopping from one side of the slack caused by a sloppy tripod head to the other.

    Diffraction would affect the whole image, and a diffraction pattern leading to a linear double image does challenge the mind somewhat.

    As Doyle said in the voice of Sherlock Holmes, when one eliminates the impossible, then what remains, however improbable, must be the truth. Film popping is the only suggestion so far that could cause the effect.

    Rick "who has certainly experienced film popping in scanners--and slide projectors" Denney

  3. #13

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    Re: "Focus" problem that is driving me insane


  4. #14
    lenser's Avatar
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    Tim from Missouri
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    Re: "Focus" problem that is driving me insane

    This looks one heck of a lot like an image that Edward Steichen did of fruit in a bowl where he had the subject under a very dark tent with only a very tiny opening for light to enter. The exposure was made over several hours (days?), and resulted in overlapping layers of sharpness attributed by him as resulting from the expasion and contraction of the lens between day and night temperatures with a resulting change of the point of focus.

    I'm voting for temperature changes first, but is there the possibility that you have the lens position raised to some extreme, on all of these images where you've experienced the problem, and that your front standard locks for either the rise or the tilt, might be just slightly slipping (maybe due to bellows tension) in such a way that it only effects the top of the images.

    Are you using a standard or bag bellows? Also, does this happen only with one camera and lens combination or does it happen with different body, bellows and lens combinations? Does your camera have center pivots for tilt or base tilts? If base tilts, it is possible that there could be a combination of a fractional top tilt and therefore focus change at the same time which could keep one area sharp and others slightly double exposed in their focus point. Extremely far fetched, but mechanically possible.
    "One of the greatest necessities in America is to discover creative solitude." Carl Sandburg

  5. #15

    Re: "Focus" problem that is driving me insane

    Wow, all these replies. This is amazing! Where have you been?

    The film pop theory makes a lot of sense. The film holders travel out with me tucked in a warm padded (insulated) case, then are suddenly exposed to a different temperature and humidity, for a 4-14 minute exposure. (yes using a cable release)

    Though my problem is not limited to winter temperatures. I can think of 3 or 4 sessions that experienced this problem in July (in northern Europe). I suspect humidity could be a significant factor. I wonder why the lower central part of the image is always unaffected, perhaps gravity plays a part somehow?

    Here's a closer look at the very top edge of frame just above the other sample I posted. This area would presumably be secured by one of the film holder edges. Sharp.


    Thinking back through the history of shooting this project (which you're welcome to view at http://www.wmokrynski.com, follow the project link to 'Nylon Chrysalis', (the project is also featured in this issue of Eyemazing Magazine)), I started off exclusively shooting with Fuji Quick Load films. Then my supply ran out, I couldn't get more within Europe, and I switched to conventional holders. Thinking about it now, I had zero (motion blur) pop issues with those early exposures utilizing the quick load film. The film must have been held nice and tight within the package.

    Has anyone else experienced film pop? I can't be the only one. Might there be a preferred film holder that would hold it more securely and prevent a pop? How long would you suggest I acclimatize the film within the camera before making an exposure? (just what I need, another step which makes the nocturnal session longer ) Do you really think tapping the holder will help? The film would have bounced around in the rolling case on the travel to the location.

    I'll post another problematic potential pop image or two tomorrow for analysis.
    I'm feeling much better about it now, though the big question is how am I assured the film has acclimatized before exposing? ...Or do I scrounge the world for all the remaining Provia Quickload film? (and plead with Fuji to restart production)

    Thanks for the help so far,
    William

  6. #16

    Re: "Focus" problem that is driving me insane

    Thanks for the diffraction information. Incredibly, I wasn't aware of it.
    Down to f11 I go.

  7. #17

    Re: "Focus" problem that is driving me insane

    A heavier tripod has been suggested to me before, though I don't think tripod is the problem here. I've had many successes with the same conditions using this tripod. Besides the 190 fits nicely in the bottom of my suitcase. Tell me how one can fly with a bulkier, heavier, tripod and not get dinged with a ludicrous extra baggage charge.

  8. #18

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    Re: "Focus" problem that is driving me insane

    I really don't think that a heavier tripod would help. This looks like film "pop" to me also. I've never had this happen to me in a camera, but as a professional printer this was a relatively common problem on big enlargements when everything was printed from negs or trannies. The effect was virtually the same as what you have here.
    Keith

  9. #19
    ic-racer's Avatar
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    Re: "Focus" problem that is driving me insane

    Based on the picture, my guess is that your not parallel with the building. Getting a 90mm lined up can be difficult. I just spend a good deal of time getting the zero detents on my 4x5 lined up because of some similar issues with a new 90mm. Though my problem was in side-to-side focus. The amount that it was off was so small that I actually wondered why there are not that many threads on zeroing the detents on 4x5 cameras with wide lenses. I can't believe everyones camera is fine from the factory with 90 and shorter lenses.

  10. #20

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    Re: "Focus" problem that is driving me insane

    From the picture alone I would agree that the film popping is the most likely problem. However, it is curious that the problem would be chronic, consistent and at the top of the image (bottom of the holder) if that is the case. I would not be surprised if there is a combination of issues.

    First, as a matter of good practice, control the easy things.
    1) Always tap the bottom edge of the holder before inserting it into the camera to be sure the bottom edge of the film is seated and the sheet wont slip down.
    2) Always let the film rest for a couple of minutes after pulling the slide. Also, I often take my holder bag out of my camera bag while I'm setting up so they can equilibrate at least partially to ambient temperature.
    3) confirm that the lens board and film holder are properly seated in the camera and everything is zeroed before making adjustments.

    Regardless of any other issues, failure to do these things will result in occasional failures for long night exposures so just get used to it.

    Now I am going to go out on a limb and suggest that you have an alignment problem. This is likely for two reasons. First, you say the in/out of focus areas are consistent over time, even if the problem is intermittent, suggesting a structural problem. Second, the area which is in focus is probably where you were able to focus. You are using a wide lens at night with rise so i'll bet you focused in the bright central area near the street level and probably couldn't have focused at the top of the building very well. This would be much less likely to occur during the day or with a long lens where it is easy to verify focus throughout the entire frame or in situations where you might focus in the center of the frame resulting in a less significant defocusing problem towards the top and bottom edges. IOW, If you have have an alignment problem setting the focus on one edge of the frame will produce twice the error in the other edge as setting it in the center and in the latter case the loss of sharpness may go unnoticed explaining why not all of your images are "bad".

    You can check this simply enough with a small bubble level applied to the lens board and the ground glass. put your camera on a tripod, zero everything, position using the level such that you can get the lens board perfectly vertical and verify that the ground glass is also vertical. With such a significant effect at f32 as shown in the image the missalignment should be fairly obvious.

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