What is the overall distortion pattern of the new (rubber ring) 55mm f4 wide angle? I'm trying to stitch together a series of exposures in Photoshop in order to create a panorama, but the overlapping image areas don't match up and it looks like it's due to lens distortion. Whatever the reverse of barrel distortion, that's what it appears to be. But applying either the Pinch or Pincushion (reverse Spherize) filters don't correct the distortion. Is this type of lens distortion non-linear?

-- Bill Baker (wab@well.com), September 06, 2000

Answers

Distortion is an aberration that involves differential image magnification and is not really like the other aberrations. It does not affect sharpness. Nearly all wide angle lenses have barrel distortion but there are a few exceptions(Biogons and other symmetricals). I don't own the 55 but I can say that it is a very different design from the 45 and both 75s. The opposite of barrel is pincushion distortion, if that helps. Through the finder, pincushion looks as if a known straight subject is bent inward toward the center of the frame when it should be parallel to the frame edge. In theory, a distortion filter should be able to correct what you are experiencing. But, it would have the be the opposite of what you have and in the same degree. I have never seen the filters you describe. SR

-- Steve Rasmussen (srasmuss@flash.net), September 07, 2000.

Bill, I recently read an issue of Goerge Lepp's "The Natural Image" that dealt with stitching images to make panoramas in the computer. He says that images must be made with a 50mm lens or longer (in 35mm format) if you are going put them together in Photoshop. They must be overlapped by 20% on each end, and the tripod legs and head must both be leveled, to get a level pan.

The only program that can put together pictures made with a wide angle lens is PowerStitch by Enroute Imaging. It has controls to deal with field of view and distortion. Lepp says it costs about $400.

He also says that more overlap is required (when the pictures are being shot) with wide angle lenses. With a 28mm lens (35mm format) a 50% overlap is needed. Bob

-- Bobby Mahaffey (mahajen@prodigy.net), September 07, 2000.

Wow, I'm basically SOL, then. Thanks for the replies, guys.

-- Bill Baker (wab@well.com), September 07, 2000.