If I knew what it was called, I could search for it!

52Caddy · March 7, 2005

Hi guys.
What is this officially called, as opposed to the leaning tower of Pisa!
I'm pretty sure the building was straight up and down.
Is this a problem with digital photography as a whole, or the result of my cheap camera?
Thanks!

amc · March 7, 2005

Perhaps this is symptomatic of shooting with a wide angle lens? I took the liberty of doing a perspective correction, and this is the result. I think the fire truck got stretched in the process!

wxwax · March 7, 2005

It's called "barrel distortion" and is the result of having a very wide angle lens. It's not yer camera. Do a Google for 'barrel distortion' or 'barrel effect' and you'll find the technical explanation. Its opposite is called 'pin cushion.'

52Caddy · March 7, 2005

Thanks guys.
It does look like the fire truck gained a few feet. Otherwise it looks good!

amc · March 7, 2005

52Caddy wrote:

Thanks guys.
It does look like the fire truck gained a few feet. Otherwise it looks good!

Just think of it as the new model "stretch engine," designed specifically for putting out fires at weddings and senior proms.

pathfinder · March 10, 2005

wxwax wrote:

It's called "barrel distortion" and is the result of having a very wide angle lens. It's not yer camera. Do a Google for 'barrel distortion' or 'barrel effect' and you'll find the technical explanation. Its opposite is called 'pin cushion.'

Technically.... Sid - I think this is perspective distortion, caused by the film plane of the camera not being held vertical to the plane of the subject, but tilted up to encompass the taller parts of the building. Perspective distortion causes objects to look like they are falling backwards BUT the lines in the image remain straight.
Barrel distortion ( http://www.dpreview.com/learn/?/Image_Techniques/Barrel_Distortion_Correction_01.htm )causes a curvature in the periphery of the image - straight lines are no longer straight. Barrel distortion is an optical defect in a lens, but perspective distortion occurs when the film plane(sensor plane) is at an angle to the subject of the photograph causing an empahisis on the nearer part of the image relative to the more distant parts.

Perspective distortion can be corrected in camera by a tilt and shift lens or a full T/S view camera which allows the film plane to remain vertical while the lens axis is raised above the center of the film surface to allow the totality of the subject to be captured without looking like it is falling backwards.. A nice discussion with pictures can be seen here - http://www.bluejake.com/archives/2004/05/24/pleasant_avenue_distortion.php

And you are correct Sid, that many images have aspects of both perspective and barrel distortion

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wxwax · March 10, 2005

Good stuff, PF, thanks. I must admit, to my failing eyes the building on the edge looks curved. I'd never considered perspective distortion.

patch29 · March 10, 2005

I have heard the perspective distortion referred to as convergence, as in the convergence of parallel lines, but the photo in question has both barrel distortion and convergence.

DavidTO · March 10, 2005

Demo this.

dkoyanagi · March 10, 2005

It's called perspective distortion. Sometimes you can use it to your advantage

David_S85 · March 11, 2005

Its all of the above.

And barrel distortion is not necessarily an optical defect in the lens, but rather a characteristic of a wide angle lens. Even the best wide angle lenses will generate a little bit of it. With fisheye wide angle lenses (not in digicams) the effect is actually intended. The rectilinear type full-frame (here meaning full coverage) wides will partially correct for the barrel effect, but only when straight lines pass through the center of the image, the remaining portions of the image are still somewhat contorted.

As the angle of shooting becomes more oblique (less straight-on) to a subject with large, tall, broad long lines - buildings and such - perspective distortion also becomes more severe. That is caused by poor shooting placement, which many times can not be controlled, such as shooting a building from below.

Correction for these problems can be done by first removing any barrel distortion. An excellent, and free, Windows-based solotion is PTLens, by Thomas Neimann.

http://epaperpress.com

With luck, your camera is listed in the profiles, which is a separate download. If not, he will do a custom correction for you if you meet the conditions listed on his site. He did some for me which took about a week. His program comes either as a stand-alone, or a plug-in version for photo editors that can accept an .8bf type file.

Perspective correction should then be done, since it is easier to view an already de-barrelized shot in the photo editor viewing window. Photoshop and Paint Shop Pro both have excellent tools for perspective correction.

One more note... not all subjects should be corrected. Sometimes, the character of a picture is ruined by messing with it. However, architecture shots, for the most part, can usually benefit from both fixes.

If I knew what it was called, I could search for it!

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