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Thread: blurring at edge of image circle without any vignetting?

  1. #1

    Join Date
    Feb 2016
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    Fredericksburg, VA
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    blurring at edge of image circle without any vignetting?

    I didn't take note of the amount of rise in this Super Angulon 90mm 5.6 f22 4x5 shot but I find it very odd that there is such a blur at top with no vignette. I used rise and no other movements. This is only the 3rd time with this lens, so maybe it is something about this lens in particular? I'm not used to shooting without a filter -- maybe it's the just the filter that tends to vignette when lens is under heavy rise/shifts?
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  2. #2

    Join Date
    Mar 2005
    Location
    Newbury, Vermont
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    2,260

    Re: blurring at edge of image circle without any vignetting?

    How clearly could you verify...prior to making the exposure - that the elements of the photograph which appear to be unsharp actually appeared as sharp on your ground glass? If all first appeared sharp on the ground glass...then either the film moved (buckled) in some way just prior to the exposure, or the positioning of the ground glass itself is incorrect, or perhaps something is wrong with the particular film holder used.

    Question: had the film holder in question been subject to any sort of environmental change (temperature/moisture) prior to the exposure? If so, these changes can cause film to buckle.

    Sounds like you need to set this specific camera and lens combination up to photograph something flat with detail (like a brick wall or interior wall to which you have flatly taped newspapers or white paper marked to edges with black lines/patterns), and in a controlled, stable environment to help ensure that film has not/will not buckle...then do your best to establish overall focus prior to taking a photograph at the same aperture (f/22) used for your original photo. Actually, take two photographs...one with film and lens aligned axially (no camera movements) and the second with a good amount of front rise.

    If at all possible, use the same film holder for this test as you'd used for your original photo. Then, if things don't look sharp, first try another holder to see if this might be where the problem is.

    There are many other tests you could try (different apertures/oblique vantage points/carefully measuring for parallelism, etc.), but you first need to verify that "what you see is what you get" focus-wise, while possibly also eliminating transient environmental variables.

    Edit: Within the realm of my response above there lies another question: how are your eyes, and/or your facility with whatever focus aid you are employing? Yet another question: did you employ the camera's rise prior to or after focussing? Always good to check both before and after...to ascertain that the lateral camera movements are indeed truly (only) lateral! Finally, seeing as this is only the third time using this particular lens, and how wide angle such as this one can, depending on the quality and design of your focussing screen (assuming its accuracy), and the efficacy of your eyes and any focussing aids, create some avenues for misjudgment (you might be wrongly assuming that your focus accuracy is optimal), or the lens could possibly be defective in some way, but your are not familiar enough with it to question its accuracy.

    So...so many variables to consider!
    Last edited by John Layton; 14-Dec-2020 at 09:25.

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