Please Advise Me. Image Distortion Question

Discussion in 'Photography Beginners' Forum' started by myopicseer, Nov 14, 2009.

  1. myopicseer

    myopicseer TPF Noob!

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    I am an oil painter, not a photographer. I plan to hire a photographer to photo my art, but for now I am tasked with this assignment. Over many years using my simple Coolpix 5700, I have always seemed to have the same problem when shooting my art:

    Slight "fisheye" (bulge) effect. I try to shoot within a range of 4 feet. I generally have tried to use the close setting (the flower icon). Inevitably the straight edges of the canvas or picture frame bow slightly outward. This drives me nuts, since otherwise the image color, exposure...everything else is very acceptable to me. I tried googling this problem, and cannot locate any reference to it at all. Is this likely a problem with the camera, with the settings or with my approach? I am absolutely clueless and would appreciate some possible insight.

    Thanks.
     
  2. Pugs

    Pugs TPF Noob!

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    Try zooming in as tight as the camera can without going into "digital zoom". Then, back up until the painting fills the frame. Use the "normal" setting to do this.
     
  3. Brian L

    Brian L TPF Noob!

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    As pugs says that should do it for ya. The reason your getting the effect is cause your shooting a wide focal length of say example 14mm. At wide focal lengths you get that effect. At a focal length of 100mm will not make what your having happen, happen. Here is an example.


    [​IMG]

    You notice with this wide angle lens her jaw and face are curved out like the effect your getting.


    [​IMG]

    But with a longer focal length such as this 65mm it tighter and does spread out the image so to say. Hope this helps on why your getting the effect a little more.
     
  4. Dwig

    Dwig TPF Noob!

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    Rectilinear distortion (so called "barrel" or "pincushion" distortion) is inherent in all lenses to some degree. It is often rather severe in zoom lenses, particularly when they are designed to be both compact and have a wide zoom range. This type of distortion is not related to the perspective alteration (often incorrectly termed "distortion") that is a product of the relationship between subject and background distances and generally associated with wide angle lenses.

    In many cases, the common wide to tele zoom exhibit barrel distortion at the wide end and pincushion at the long end. Somewhere in the middle of their range, though perhaps skewed toward one end or the other, there is a focal length where the distortion is very small or even non-existent. With some of the better SLR lenses there are published test reports that can guide you to finding the zoom setting with the least distortion. With P&S cameras, such reports are extremely rare.

    You can easily test the camera yourself. Set up a test environment where you can shoot straight at a subject with a good grid pattern and fill the frame from the same position at all zoom settings. A brick wall is usually a good choice. Be sure you line of sight is exactly perpendicular to the face of the wall in all shots. Simply shoot one shot at full wide, tap the zoom button to nudge toward tele, shoot again, repeat. Review the pix carefully on you computer monitor to see which yields the least distortion. Then when shooting your art always use that zoom setting. With my Nikon CoolPix 8400, the least distortion is about one tap wider than the max tele position.

    Even if you move to a DSLR, this problem will exist. With DSLRs, the best solution is generally to use a non-zoom (aka "prime" or "fixed focal length") lens that is a normal or slight telephoto. Often the choice is a "macro" lens where extra effort is made in the lens design to reduce distortion. Most of the common 50mm lenses currently available for DSLRs are also good choices.
     
  5. PHILLIP MAC

    PHILLIP MAC TPF Noob!

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    The longer the lens the less distortion, but the most difficult thing with reproducing paintings in the studio is lighting, particularly if the paint is applied with a knife or thick brush.
     
  6. myopicseer

    myopicseer TPF Noob!

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    You folks really know your craft. Thanks for being so generous with your time and help, and for not being a bit condescending--which would be easy to do since I am just clueless. But you made the issues understandable; I have to say though, I have a new respect for photographers. I knew that it was both an art and science, but never realized how many technical considerations were involved. I will shoot a grid as suggested to see if I can determine the optimal focal length. The lighting problem I have been aware of, and my paintings are varnished. The texture of the canvas weave, even, presents star-like points of light problems. I bounced the mounted flash unit off the ceiling and was able to get a moderately acceptable result. I had to use the CS4 Distort Filter Lens Correction feature to square the edges (not the best solution, but it helped). You can see the image at blixies [DOT] com/index.php?page=shop.browse&category_id=4&vmcchk=1&option=com_virtuemart&Itemid=10
     

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