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Thread: Lens distortion?

  1. #1

    Lens distortion?

    Hi All,
    Not sure what caused this issue. I would like to blame the lens but I have a sinking feeling it is me I have a very hard time getting the camera dead on 90' to the wall. For some reason these days I like walls so it is an issue!

    I spent a lot of time getting this straight as there were too many lines for any to be off. I checked camera position and level a few different ways. I thought I was very close to dead on.

    The lens was a Rodenstock Sironar-N 240/5.6 MC shot from the deardorff F45 1/8th' about 15 feet away fom the wall.

    I have LR3 and if I add about 6% of positive distortion correction it all looks great

    thanks

    straigh scan no correction


    small-8.jpg by urbanlandcruiser, on Flickr
    david

  2. #2
    William Whitaker's Avatar
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    Re: Lens distortion?

    What's the problem?

  3. #3

    Re: Lens distortion?

    the middle is pushed out. the wall is flat but the middle is concave.

    here it is corrected at +6%. It is not a perfect fix ...it is not even a good photo but I have run into this before and want to nail down the cause. I left the original border show one can see amount/type of correction


    small-8.jpg by urbanlandcruiser, on Flickr
    david

  4. #4

    Join Date
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    Re: Lens distortion?

    That does look like massive barrel distortion on the order that I've never seen in any LF lens I have owned or viewed pictures taken with. I suspect something else is wrong, but don't know what. Maybe it is your scanner? Or the way the film was sitting in the scanner? So, does it look that way on the neg?

  5. #5

    Re: Lens distortion?

    Film was dead flat on the scanner. I looked at the neg on the light table and it is difficult to tell exactly but I am 99% sure it is there on the neg. The LHS window is wonky on the neg as well as the scan.
    david

  6. #6

    Join Date
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    Re: Lens distortion?

    Then that is beyond my fathoming. I can't imagine that that particular lens would have that kind of distortion. Maybe you can do some further test shots from various distances and see if it is related to that?

  7. #7

    Re: Lens distortion?

    I think it is due to the distance to the wall but I have never seen anything like this. I cant help but think there is another reason...outside of the monkey in back of the camera
    david

  8. #8
    Richard K. Richard K.'s Avatar
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    Re: Lens distortion?

    It's funny , I have a favorite detailed building wall near me that I use for testing lenses and it's not easy squaring everything up, especially the correct azimuthal orientation (no levels for that adjustment!). But that's not the problem here. Is it possible that your back (well, the camera's back actually!) was slightly out of vertical and focus top and bottom was achieved by a correcting slightly tilted front?
    When I was 16 I thought my father the stupidest man in the world; when I reached 21, I was astounded by how much he had learned in just 5 years!

    -appropriated from Mark Twain

  9. #9

    Re: Lens distortion?

    It is very possible.

    I first checked level both directions with the bubble levels on the head. Once in "more or less level" I compose then level by eye on the GG then I whip out my trusty 7" level and put it on the rear standard to set both axis to 90' after which I go back to the GG and make sure we are still correct. I did that twice. I did not fool with the ft much except to make sure it was more or less in line with the rear standard.

    This is a deardorff after all....the F150 of the LF world and mine is more wonky than most. I could easily have misjudged the level on the rear.

    The big question is if the rear standard is slightly out of whack would it produce this effect? I am a bit lost as the center bricks are correct and the distortion seems to get worse towards the edges...as a lens would.
    david

  10. #10

    Join Date
    Jan 2011
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    40

    Re: Lens distortion?

    Maybe the wall is not straight.

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