What's up with my lens/image quality?

Hi all,

Picked up a Canon 17-85 IS USM off adverts not too long ago. Been using it and have been happy enough with it. I do notice an issue with it though, and it's something that, whilst it somehow doesn't seem to affect every image, it does appear now and then and is a pain.


Here's a photo from Friday night (note; there is a better version of the photo that's not as snapshot-ish, but it didnt really show what Im talking about, so don't go judging me based on this imagery! ).




17mm, f/7.1, 1/100, ISO 400


(Should be able to view it full size by clicking through to Pix, and just to note; I shot raw, took the photo into Camera Raw, saved it as a Jpeg and uplaoded it, so it hasn't had any editing)



Now, it was just a test shot, but the girls in the centre seem reasonably sharp to me. If you zoom into the smiling girl in the black dress in the centre of the image, she looks grand. She looks how you'd expect her to look. However, if you scroll over to the girls on the extreme left or right, they look a bit odd.

I looks like they're getting pushed or smudged or something by the lens? Ignorning the chromatic abberation that seems to be running wild on them, I can't understand this. I know that 17mm is gonna cause some distortion, but this seems a bit strange to me.


Any ideas?

challengemaster

It's lens distortion, it happens when you go very wide angle, basically you start approaching fisheye angle, and as such, the image at the edges starts to curve.

Here's a better explaination with images...

http://www.dxo.com/us/photo/dxo_optics_pro/optics_geometry_corrections/distortion

You've 2 choices. Use distortion correction is PS / editing software if you can, or try avoid it by using your feet, moving back and not going so wide on the lens

I understand distortion at 17mm will be noticeable, but this looks like it's almost scratching them as it pulls them to the side.

Are you sure it'd be just the distortion? or am i trying to invent problems that aren't there?

gizzymo

That is the distortion. I'm a professional photographer, I'm 100% sure

Pete

hbr

Deleted User wrote: »

Are you sure it'd be just the distortion? or am i trying to invent problems that aren't there?

Most lenses are sharper at the centre of the image than they are at the outer
edge of the image circle.

Your picture shows a slight lack of corner sharpness, chromatic
aberration and quite a bit of barrel distortion (look at the top of the bar). This is
not unusual for a zoom lens at the wide end of the zoom range.

AnimalRights

I discovered this with my 17-40L and 24-105L a few years ago, I've since traded both in since and got the 24-70L which handles it far better and funnily enough its taught me how to use my fisheye properly, Challengemasters post is perfect for laymans terms.

Cheers guys.

I thought maybe I was having a problem or two. I know about distortion and it's appearance at different focal lengths, but this is my first time having continuously to run into it, and i thought that because the quality of the image suffered so much at the sides, that maybe it wasn't just the distortion.


Cheers for the replies.