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Thread: "Focus" problem that is driving me insane

  1. #31

    Join Date
    Sep 1998

    Re: "Focus" problem that is driving me insane

    Quote Originally Posted by Brian Ellis View Post
    The effect of diffraction would show up as an overall "softness" of the image, it wouldn't cause only part of the image to be unsharp while other parts are sharp.

    Tobasco, your technique sounds fine. I'd check for film "pop" as many others have stated and also a bellows or lens board leak. I had a lens board from which a cable release gizmo had been removed, leaving a small hole in the board. I foolishly didn't think to cover the hole and the resulting photographs looked a lot like what you're posting. So it's probably a long shot but worth checking.
    To quote Rodenstock in several of their lens brochures:

    "Depending on the reproduction ratio and the depth of the motif (subject), the required depth of field may make further stopping down necessary. In such cases, the sharpness may be reduced due to diffraction - particularly in the center of the image circle."

    The above appears in their taking lens brochures.
    The following is from their Apo Rodagon-N brochure:

    "Sharpness and contrast are at a maximum over the whole image field. While stopping down further will produce a slight increase in sharpness in the extreme corners, the performance in the center is reduced due to the effects of diffraction."

  2. #32
    Join Date
    Apr 2010

    Re: "Focus" problem that is driving me insane

    But diffraction affects the entire image equally, it sets a limit for the resolution. In practice, the image is sharper in the center, so that is where the limit is reached first. Diffraction never brings center sharpness below corner sharpness.

    As Brian Ellis said, diffraction shows up as an overall "softness".

  3. #33
    Virtually Grey Steve Gledhill's Avatar
    Join Date
    Oct 2007
    Evesham, UK.

    Re: "Focus" problem that is driving me insane

    Film popping is certainly at play here. Please see this previous post from me where I quote some excellent advice from John Sexton.

  4. #34
    Jim Jones's Avatar
    Join Date
    Aug 2006
    Chillicothe Missouri USA

    Re: "Focus" problem that is driving me insane

    Quote Originally Posted by engl View Post
    . . . Diffraction never brings center sharpness below corner sharpness.

    As Brian Ellis said, diffraction shows up as an overall "softness".
    In practical photography this is true. However, in wide angle pinhole photography with a slightly oversize pinhole, sometimes edge resolution exceeds center resolution.

  5. #35
    Andrew L
    Join Date
    Feb 2011

    Re: "Focus" problem that is driving me insane

    I'm pretty new to the whole large format thing, but I want to either go with this film pop (though I really think it odd that this would happen so much and to such an extent just from my experience with things changing in different temperatures and humidity).

    How good is this "135mm Rodenstock lens?" For some reason I'm thinking that is one of the better brands, but how much are you adjusting the camera, like rise I guess it would be. Is it extreme or just a little? Not having much experience with LF, I would guess that you're getting near the edge of the image circle and it's getting wonky? I could be totally off, but that's just my guess.

  6. #36
    Format Omnivore Brian C. Miller's Avatar
    Join Date
    Jun 1999
    Everett, WA

    Re: "Focus" problem that is driving me insane

    Hi, Andrew! If you take another look at the images, you'll see that the problem is that all of the corners are in focus, while the center starts going "soft" in a movement sort of way, not a focus sort of way. The film itself moved while the exposure was being made.

    If you develop film yourself, you'll see it pop back and forth as it dries. A similar thing happens inside the camera when the film's temperature hasn't stabilized.

  7. #37

    Join Date
    Apr 2009

    Re: "Focus" problem that is driving me insane

    I, too am having this issue with film popping with 8x10. For 4x5 I use a small piece of two-way tape which works for 90% of my long exposures in the damp night air, but it isn't working for 8x10. Maybe there is too much surface area. I am waiting about a minute with the lens closed and the slide pulled for the film to stabilize before I start the exposure. The vacuum holder sounds like an excellent option but making one doesn't.

  8. #38

    Join Date
    Aug 2000

    Re: "Focus" problem that is driving me insane

    Ray McSavaney is a master at making long exposure images,often up to an hour.
    Hi solution:
    1. Film holders are not only light proof, but to an extent air tight. Thus when the film is loaded in one environment and then exposed in another the relative humidity will almost always produce some film pop.
    2. Set up the exposure, insert the film holder, cover the camera with the dark cloth and remove the slide.
    3. wait 5 minutes and then open the shutter for the exposure.
    4. this will take care of the most extreme changes in temperature and humidity. When making an extra long exposure an extra 5 minutes does not matter.

  9. #39
    runs a monkey grinder Steve M Hostetter's Avatar
    Join Date
    Jul 2008
    Beech Grove Indiana

    Re: "Focus" problem that is driving me insane

    Building movement

    It may be a calm night where your standing on the street but go up 30 stories and feel something else

    I would imagine the visqueen covered scaffolding has to be moving somewhat

    Last edited by Steve M Hostetter; 12-Jul-2011 at 08:05.

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