In general, barrel distortion gives you a barrel shape, much like parenthesis facing each other. Perspective distortion gives you a pyramid shape. The outer verticals lean in. Perspective distortion is easy to correct in PhotoShop using Edit/Transform/Perspective. After correction, you have to crop, and you'll lose a bit of the frame. Frequently, I apply just a small amount of correction. You don't want perfectly aligned verticals for most shots.
Barrel distortion can be corrected as well, but it's more difficult and usually not necessary. In PhotoShop Edit/Transform/Distort can help some, but there are third party lens correction tools that do a better job. However, I don't find that any of my lenses, including the 16-45 and 12-24, produce severe enough barrel distortion to require correction for normal use. I only remember using such a tool once. It was for a 12mm shot that included a vertical right near the edge of frame. A tiny bit of barrel distortion was visible after the perspective had been corrected. Rob told me how to fix it, and I did, but I don't remember the specific tool I used. Paul On Nov 9, 2007, at 11:19 PM, [EMAIL PROTECTED] wrote: > I can't call this a stupid newbie question, because I am not a newbie > anymore. ;-) > > Previously I have not shot much with wide angles. I used my Canon > 17-40 in > Yosemite and thought I noticed some trees leaning in slightly in > some shots. > But only slightly. > > I have noticed a lot of distortion using the 16-45 on the K100D. > While > sometimes I don't mind this, other times I have been annoyed > because I wasn't > taking it into account. I am also reassessing the lens. > > However, I realize I am not all that clear on the difference > between barrel > distortion and perspective distortion. > > I also realize that getting more in the frame than normal > perspective would > allow must mean something will happen. > > I am curious if there is a formula for when perspective distortion > will not > occur, or some focal length at which it will not occur? Would > about 45mm be > the cut off point -- it won't occur at 45mm? As for barrel > distortion, it > seems to be depend on the lens. It seems people use brick wall to > test for barrel > distortion. Is that true, some wide angles have barrel distortion > and some > do not? Or do they all to some degree? > > As you can tell, I am not quite sure how to phrase this question. > > Basically what I want to know is when I shoot with the 16-45 when > I will get > some distortion and when I am likely not to. So I can take it into > account > and plan for it. And use the 16mm end or zoom in a bit more to > avoid it when I > want to avoid it. > > And anyone who wants to expound more on the difference between barrel > distortion and perspective distortion, too, feel free. I am pretty > clueless on the > whole topic. > > I think this is perspective distortion... (which I don't mind in > this case, > but this is not the strongest example, just one I have shown) > > http://members.aol.com/eactivist/PAWS/pages/temple2.htm > > I think this was may be barrel distortion. When I looked at it I > found the > lamp post leaning in, so I straighten the picture in Elements 5 with > Transform/Skew. Hence the distortion isn't showing anymore, but it > was there. > > http://members.aol.com/eactivist/PAWS/pages/bars.htm > > I can go back and look at exitf if needed, but I think the top was > shot at > 16mm and the lower one longer. > > TIA for anything you want to offer, Marnie aka Doe :-) > > --------------------------------------------- > Warning: I am now filtering my email, so you may be censored. > > > > > ************************************** See what's new at http:// > www.aol.com > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above > and follow the directions. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
