Whats this called again?

[jewels52]

Hello-
I am testing out my new 17-40L with my 20d. I took this shot in low light in my bedroom with flash at the widest (17mm). There seems to be a distortion like the image is warping, like on a slight curve. This doesn't happen at 40mm. Is this normal for my new lens? What is this called again? pincushion distortion?
70823

[scraggles]

it happens up close. Try taking a self portrait with the lens at 17mm. It gets amusing.

[Tom W]

Barrel distortion. The image gets "rounded" a bit. This is common with ultra-wide lenses, though some do better at controlling it than others. You'll find that the 17-40 has a fair amount at 17 mm, but as you zoom longer, it disappears quickly.

The opposite distortion is "pincushion" where the corners seem to spike outward a bit. Many zooms that have barrel distortion at the widest focal length have a bit of pincushion distortion at the longest focal length.

BTW, is that a lava lamp on the right side of the bed?

[jewels52]

so this is normal? Even with an L lens? Is it called pincushion distortion?

[jewels52]

Thanks Tom, Pheeww...thought it might be a bad lens...thank god its normal.

[Tom W]

The rounding effect is barrel distortion. The effect where the corners appear stretched out away from the center would be pincushion distortion.

[jewels52]

oh...and no lava lamp, just my IKEA bedroom. ;)

[Tom W]

oh...and no lava lamp, just my IKEA bedroom. ;)

Looks like there might be a body under the blanket. ;)

j/k - here's a shot from one of the gazillion lenses I've tried over the years. It has some barrel distortion, but towards the corners, the corrective lens elements creates a bit of pincushion distortion. A few people have called the combination "mustache" distortion:

http://www.pbase.com/photosbytom/image/53824286.jpg

[mbze430]

pincushion at the wide-angle and barrel at the telephoto end. Learn please

[Tom W]

pincushion at the wide-angle and barrel at the telephoto end. Learn please

Generally, it's the other way around - pincushion usually occurs in the realm of the longer lenses while barrel distortion is typical at the wide end. Paul Van Walree has a good writeup on the issue here:

http://www.vanwalree.com/optics/distortion.html

[mbze430]

pincushion at the wide-angle and barrel at the telephoto end. Learn please

oops, it is the opposite of what I wrote.

[RichardtheSane]

Looking at this shot I can see a little barrel distortion, but there is also a shift in the persective which is caused by the camera not being perpendicular to the uprights
(Think I explained that right)

[FlashZebra]

I am not seeing very much distortion in the image either. I think there is a bit of "keystoning' due to the fact the camera was tilted upwards a bit.

If you had the camera level the "keystoning" would go away. If you wanted the same view, you would need to stand on a chair (or some such thing) so the camera would be level yet still get the same perimeter you have in the image.

I would be very happy with this geometry on a 17mm lens.

That curved blind also plays with your mind a bit. But there is nothing really distorted about it, just pushed out at the bottom by something.

Enjoy! Lon

[RichardtheSane]

Keystoning, that's a much better explanation than mine!
Thanks Londuck