Unsharp Images

Discussion in 'Exposure Discussion' started by Dan Henderson, Oct 28, 2005.

  1. Dan Henderson

    Dan Henderson Member

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    Last summer I made a number of exposures of large waterfalls in Michigan's Upper Peninsula. Now that I have time to make decent size prints, I see that many of them are unsharp. All were shot on 100 speed film, at f/22 or f/32 depending on lens used with a Hasselblad 500CM, at exposure times of 8 to as much as 30 seconds to get nice water blur, and using mirror lockup and cable release. Images made at shorter shutter speeds are fine.

    I'm thinking that a small camera shake was created by the power of the water at the base of the falls that produced the unsharp images. Has anyone else experienced a similar problem while photographing near waterfalls?

    Thanks,
    Dan
     
  2. Ole

    Ole Moderator Staff Member Moderator

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    Were the other shots shot at wider aperture? If so, you could be seeing diffraction. At f:22 and f:32 the sharpness would certainly be diffraction-limited.
     
  3. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    With medium format, I suspect camera movement with an 8-30 sec. exposure more than diffraction at f:22 or 32. At those speeds mirror slap and shutter vibration shouldn't really be issues, but wind vibration and too light a tripod or head could be. I suppose if the waterfall is big enough and you're close enough, there could be some ground vibration.
     
  4. rbarker

    rbarker Member

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    I agree with David - the source of the problem is most likely from camera vibration due to an insufficient tripod. Diffraction usually doesn't rear its ugly head until the aperture is around f/45-f/64 or so.

    The vibration could be the result of either wind buffeting or ground vibration. While the wind movement is usually obvious, the transmission of ground vibration up the legs of the tripod is less obvious. Adding weight to the tripod, by hanging a rock bag or even the camera bag from the center post, often helps. Vibration can also be reduced by adding some form of support between the legs, thus dampening the vibration.
     
  5. BWGirl

    BWGirl Member

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    I had that problem the first time I went on the UP Waterfall trip through the school. I only had my 35mm at the time, but I used a lightweight aluminum tripod. I'd never done shots at waterfalls before, so I was thinking 'backpacking' not stability. :sad:

    Now I take my Bogen-Manfrotto. If there is vibration, there's not a lot you can do regardless of the tripod. Ralph's got the right idea! One of the guys in one of my camera clubs has a weight he hangs on the underside of his tripod.

    Which falls did you go to?
     
  6. Dan Henderson

    Dan Henderson Member

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    thanks everyone for the comments. I use a pretty heavy old Bogen tripod and a decent weight head as well. As I recall, wind was not an issue, especially ones shot early in the morning with fog rising off the falls.

    BW Girl: I had problems at Bond Falls and Miner's Falls, both big falls. The thing that makes me lean toward ground induced camera shake is one image I made in mid afternoon in bright sun with an obviously shorter shutter speed. And, it may have been taken from the foot bridge at the bottom of the falls which could have insulated my tripod from shake.
     
  7. CPorter

    CPorter Member

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    Ok, since it has been mentioned here----I have to ask just exactly what is diffraction in relation to the function of the lens, can it be mitigated by using the hyperfocal distance of the lens at the apeture that was used?
     
  8. BWGirl

    BWGirl Member

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    I've found at Bond Falls, I have much better luck leaving the walkway and getting down to ground level. My poor tripod has been in that water more than a few times! :smile: Good thing my Merrells are waterproof! :wink: That first time was the only time I'd expereinced any shaky images. Hm.
     
  9. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Diffraction occurs when light bends around the edges of the aperture, softening the image. Pinhole images show a heavy amount of diffraction, so even while everything is "in focus" (i.e., within the DOF range) in a pinhole image, the whole image is soft. As you stop down the lens, diffraction increases, so you don't want to stop down more than necessary to get the DOF needed for the image you are making. On the other hand, inadequate DOF is usually more of a problem than diffraction, and most lenses are designed not to stop down to the point at which diffraction would become excessive (e.g., lenses for 35mm cameras don't usually go past f:22 or 32 at the most).