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Goldfly29
01-07-2006, 01:02 PM
My 18-200 VR arrived last night, and as promised, I took some test shots to check for distortion. These first two were both taken at 18mm, the first at f/5.6 and the second at f/3.5. I'm no expert on distortion, this is for the people who are and really care about such things. As far as I can tell though, both of these show pretty obvious barrel distortion. It's painfully obvious in the second one, and the titled lampost / gently curving roof in the first reveal quite a bit too.

ktixx
01-07-2006, 01:15 PM
What I am seeing in both those shots is not really barrel distortion as much as converging lines which happens when you point your camera up to take a shot. Take a look at this link (http://www.photo.net/equipment/canon/tilt-shift) on Tilt-Shift Lenses that will better help you understand coverging lines and why they happen. As far as barrel distortion goes, both those pictures were taken at 18mm (27mm w/crop) which is wide angle which will usually produce some mild barrel distortion. The Lampost in the first picture is right near the edge of the frame which is where barrel distortion is the worst. Again though, to me it looks more like converging lines then barrel distortion.
Ken

K1W1
01-07-2006, 01:40 PM
Yes I don't think that they are good tests.
Try taking a picture straight on to something, say a painting hanging on a wall where the focal plane of the camera is parallel with the picture.

coldrain
01-07-2006, 02:14 PM
The 2nd photo very cleary shows barrel distortion (look how the horizontal lines of the cabinet bend) but nothing shocking for a consumer lens of this range. I think my Sigma 18-50 f2.8 EX DC has about the same barel distortion. What is more bothersome is that the 2nd photo is not in focus ;)

erichlund
01-07-2006, 07:46 PM
What I am seeing in both those shots is not really barrel distortion as much as converging lines which happens when you point your camera up to take a shot. Take a look at this link (http://www.photo.net/equipment/canon/tilt-shift) on Tilt-Shift Lenses that will better help you understand coverging lines and why they happen. As far as barrel distortion goes, both those pictures were taken at 18mm (27mm w/crop) which is wide angle which will usually produce some mild barrel distortion. The Lampost in the first picture is right near the edge of the frame which is where barrel distortion is the worst. Again though, to me it looks more like converging lines then barrel distortion.
Ken
On the china cabinet, look at the top and bottom of the glass case. Barrel distortion can be detected in more that just the vertical lines, but also in horizontal ones. Still, it would be better to have a straight on shot.

erichlund
01-08-2006, 01:54 PM
this ought to settle the issue about barrel distortion at 18mm. I know they don't build houses like they used to (did they really ever?), but this door doesn't look anything like this:

http://eric-lund.smugmug.com/photos/51579592-M.jpg

So, either there is some significant barrel distortion, or what's inside that closet is about to explode. :eek: :eek: :eek:

Cheers,
Eric

coldrain
01-08-2006, 02:10 PM
Lol, don't tell me you are about to come out of the closet, Eric!!! :p :eek: ;)

I think the barrel distortion is quite a bit worse than my Sigma 18-50 f2.8 EX DC, I will try tomorrow to see how much it actually is since this picture made me curious about that.

K1W1
01-08-2006, 11:00 PM
So you visited the Hobbit village in NZ during the Christmas break. All the doors look like that! :D