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Old Jan 23, 2006, 6:10 AM   #1
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I've had this lens for over a year now on a 300D.Its been good to me since yesterday.As i was framing this photo i noticed vertical distortion on the left side even though the towers were perfectly straight.This was at 18mm.I also tried at 28,25,40,55 and the same thing.Stopping down the lens did not improve things.The lens was fine last week.I haven't dropped it or anything.I belive some of the internal elements might have missaligned,but im not sure.What do you guys think?


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Old Jan 23, 2006, 4:20 PM   #2
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I think this may be normal wide angle lens distortion. If you import the photo into Photoshop and rotate it so that the center tower is vertical, both sides lean inward equally.
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Old Jan 23, 2006, 4:23 PM   #3
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i did that and also played with the prespective correction,but that didn't seem to cure it.Anyway my point was that this didn't happen before.It also happends at 55mm
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Old Jan 23, 2006, 8:22 PM   #4
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well, if there are really noticable distortions at 55, then I think the lens busted up... somehow... if it's always noticable in the same area in every picture then I'd try replacing it... unless if you have it under warrenty.

did you try different lenses? I doubt it's the body but you never know...

time for an upgrade!
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Old Jan 23, 2006, 8:28 PM   #5
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Time for upgrade it is.I've been thinking about the Sigma 18-50 F/2.8 for a while now,i believe its a good step up.I've spend a few minutes in PS CS2 and here is the result.The lens normaly is attached to the camera in a LowePro Computreker but i guess a bump on the road might have done something to the lens.Its not the body im sure of it.Tomorrow im setting it on a tripid and will do some tests.
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Old Jan 23, 2006, 8:34 PM   #6
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All cheap (and some not so cheap) wide angle lenses suffer from barrel distortion. The kit lens is pretty awful at 18mm. I lived in Shanghai 'til recently and so all my pics had loads of buildings (and thus straight lines) and the distortion was very noticeable. You can correct it in photoshop by using pin-cushion distortion until all the lines go straight again, and then correct the perspective.
I doubt you would notice it at all though in pics without buildings in them.
The sigma 18-50 is a little better (much better at other things but still has barrel distortion) but you really need to get a prime to correct this.
The new ultra-wide zooms (10-20) are the best bet for zooms with low wide angle distortion.
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Old Jan 23, 2006, 8:38 PM   #7
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well my kit lens wasn't like that just a week ago.I've shot quite a few castles and buildings and it was never that bad.(mind you it is my third, i wasn't happy with the 2 before that so had to change cameras too,anyway all free).The 10-20 is another lens on my shopping list as well as the 105mm Macro and the 70-200 F/2.8 ( or possibly the 100-300 F/4 or 120-300 F/2.8 which i sometimes dream of :P )


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Old Jan 24, 2006, 8:50 AM   #8
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Try this little experiment. Bring the original shot into Photoshop. Pull a guide over to the bottom center window on the big tower in the middle. Now, rotate the image so that the two windows on that tower are aligned vertically. Pull a guide over to the base of the far left tower, then pull a guide to the base of the far right tower. You'll see that both lean inward at approximately the same angle. I think what you're seeing is wide-angle distortion which looks more pronounced on the left side because the picture plane is not level, and there is more mass on that side.
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Old Jan 24, 2006, 9:34 AM   #9
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This lens, cheap as it is, is pretty indestructible, and it is isn't that likely that its internal elements can go out of alignment without some serious impact.

To illustrate my point, my own 18-55mm kit lens was sitting on the kitchen table some 6 months ago and I asked my son to pass it to me. The camera bag was also sitting on the table and the lens was sitting between the loops of the bag strap. He had to move the bag to pick up the lens so what does he do, grab the bag and fling it aside (:shock catching the lens around the base and catapaulting it across the room where it smacks into the wall with a sickening thud and falls to the ground from about 1m up. I picked it up and saw the lens barrel had bent in the housing and jammed. :evil:



Anyway, upshot was that I went and bought a new lens to replace it so I figured what the heck and placed the lens under my foot and forced the barrel back into place with a loud snap, and figured just for kicks I'd put it back on and see if it worked. And cut my legs off and call me shorty the bloody thing worked with no appreciable difference to how it did before it tried to fly. I still have it going and it still works perfectly.

So I tried my hardest to wreck it and it still didn't break!

Looks like normal barrel distortion to me and can be minimised to some extent by adjusting the angle of the camera to make the camera perfectly level. Pointing it up or down will accentuate the barrel distortion.
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Old Jan 24, 2006, 11:08 AM   #10
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I'm not 100% sure, but DxO optics may be able to correct that kind of distortion. I have not checked the availability of the kit lens in DxO but last time I looked it was fairly comprehensive.

H
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