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Old Aug 14, 2005, 10:56 PM   #1
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I have a Canon Digital Rebel XT. At what focal length (wide angle) will it begin to show the "fish eye" type of picture? (The rounded effect.) My kit lens (18 - 55mm) seems OK at the 18mm setting. How much lower (15mm, 12mm or ?) before the pictures are distorted? I need to take indoor pictures of rooms in houses, condos etc. for real estate publications. TIA.
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Old Aug 15, 2005, 3:32 PM   #2
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Get the lens you need to get the shots you want and learn to take the distortions out in post processing.

PT Tools is free and has sophisticated abilities. It is mainly for panoramas, but has all the tools you need to get a flatter looking image.

There is also specialized plugins for fisheye lens distortions. This is one I ran across: http://www.richardrosenman.com/lenscorrectorpro.htm It would probably be a lot easier to use than PT Tools and is only $20. It works in just about any image editor you might use – even some freeware like Irfanview.

CS2 has some distortion corrections, but I don't think it is appropriate for fisheye effect.

See what PTLens does for your 18mm shots. It is also free and very easy to use. By taking out barrel distortion it does some distortion corrections. It might make a wider angle more useable. http://epaperpress.com/ptlens/

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Old Aug 15, 2005, 8:38 PM   #3
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Slipe is right about barrel and pincushion distortion. As he notes, those can be corrected to a fair extent and the amount of distortion a lens has depends more on the price than focal length.

In addition, there is projection distortion. About as wide as it is possible to show an image without distortion is something like 120 degrees. That translates to something like an 11 mm (equiv) as the shortest possible rectilinear lens. I am pretty sure no one has built such a lens, but Nikon does have a 14mm rectilinear lens.

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