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demorier
January 22nd, 2010, 23:50
I have a Canon IXUS70 digital camera. I have a problem with curvature of flat lines/surfaces in the image. Doesn't seem to matter if it's a wide panoramic shot or a close up type of thing, if there is a straight line in the frame it comes out curved. Anybody know how to get rid of this problem.

I've attached a photo I took a while back.

Moparmike
January 23rd, 2010, 01:05
It's pretty much a limitation of the lens on your camera.

Looking at the EXIF data for that shot, the focal length was 6mm which is very wide-angle and that will inherently give you a fisheye effect. You've also got a little vignetting (the dark shadows in the corners) caused by that extreme wide-angle too.
Depending on what you've got for image editing software there might be some possibilities to correct the fisheye effect.

Here is a cheap-n-dirty rework using PS.
-Rotated the image just a hair to level the horizon (something like 0.2°).
-Applied a slight lens correction to pull the horizon straight.
-Applied a bit of vignette correction (actually I think I overdid it a bit).

Do you have any examples using the fully zoomed & mid-range zoom to post up here? 12mm-17mm shouldn't be all that bad of a focal length for a little point-n-shoot so these shouldn't distort or vignette nearly as bad.

demorier
January 23rd, 2010, 02:24
Hi there MM. When you say PS are you referring to PhotoStudio...or maybe Photo Shop ??? I guess it might be photoshop ?

Kiwikat
January 23rd, 2010, 06:29
Yup, Photoshop.

JorisVandenBerghe
January 23rd, 2010, 07:58
Distortion is indeed a well known problem with wide angle lenses. The focal length where it happens is mostly between 35 and 10mm (I know there's a Peleng 8mm but that's a fisheye so it gets distorted images anyway)...

Comes in two variants: barrel distortion and pincushion distortion. The former occurs at a wide-angle setting while the latter may occur when you'd zoom in a bit more.

Consequently, most lenses (especially the ones with both a bit of a telephoto capability and a wide angle setting) suffer from it. The 18-55's, 18-135, Canon's 15-85, Nikon's 16-85, Sony's DT 16-80, 16-105, 11-18, Sigma's 10-20, superzooms like Tamron's 18-270, 18-200, 18-250 practically all have this problem, I guess...

For DSLR users, if there's a review at SLRgear.com of the lens you're willing to buy, you can check it there.

The only real solution to avoid distortion is either a prime or a lens like a 16-35 - the equivalent of barely 2x zoom...at least, that's what I would expect, please correct me if I'm wrong :kilroy:.
The Canon and Nikon versions seem to be pretty good when as far as distortion is concerned...

Moparmike
January 23rd, 2010, 09:16
Hi there MM. When you say PS are you referring to PhotoStudio...or maybe Photo Shop ??? I guess it might be photoshop ?

This was done with PhotoShop.
PaintShopPro X2 has many of the same features...the only one I coudn't find was the correction for the vignetting (this might need an extra plug-in...I'm still learning my way around PSPX2. I had to upgrade since PSP8.1 wasn't working on Win7 anymore)


Distortion is indeed a well known problem with wide angle lenses. The focal length where it happens mostly between 35 and 10mm (I know there's a Peleng 8mm but that's a fisheye so it gets distorted images anyway)...

Comes in two variants: barrel distortion and pincushion distortion. The former occurs at a wide-angle setting while the latter may occur when you'd zoom in a bit more.

Consequently, most lenses (especially the ones with both a bit of a telephoto capability and a wide angle setting) suffer from it. The 18-55's, 18-135, Canon's 15-85, Nikon's 16-85, Sony's DT 16-80, 11-18, Sigma's 10-20, superzooms like Tamron's 18-270, 18-200, 18-250 practically all have this problem, I guess...

For DSLR users, if there's a review at SLRgear.com of the lens you're willing to buy, you can check it there.

The only real solution to avoid distortion is either a prime or a lens like a 16-35 - the equivalent of barely 2x zoom...at least, that's what I would expect, please correct me if I'm wrong :kilroy:.
The Canon and Nikon versions seem to be pretty good when as far as distortion is concerned...

What Joris says is also applicable to all the little point-n-shoot cameras too.
Except the numbers wind up being different since most PnS cameras have these tiny little sensors compared to what they use in most DSLR or larger "pro-sumer" fixed-lens digitals.
Your 6-17mm lens on that little Canon is probably comparable to an 18-55mm on my DSLR due to the different size of the sensors.
(It's much the same as a regular 50mm prime lens on my APS-C sensor being more equivalent to 88mm on a 35mm film camera)