Straight Edges and Barreling

MonkeyChewTobacco · Sep 18, 2009

I'm about to become a first timer at commercial photography. I have to take pics of a number of doors. The doors are maybe 18 inches x 12 inches (0.5 metres x 0.3 metres). The pics will be used on a website.

I'm planning to take the pics outdoors - it is always cloudy where I live.

What's bothering me is that I'll be wanting to crop the images to the straight edges of the doors and resize to a standard size. But will I have problems with barreling of the straight edges?

Would it be better to move the camera away from the object and then use the 3x zoom, or no zoom and get in a bit closer?

Any thoughts?

Big Mike · Sep 18, 2009

Distortion, like barreling, is mostly a product of lens design...so I can't say if it will be a problem for you or not.

robertwsimpson · Sep 18, 2009

usually barreling is less evident at the zoom side of a lens, so zoom in, step back, and take the picture. see if you like that better.

MonkeyChewTobacco · Sep 18, 2009

Thanks, Mike

I should have mentioned I'll be using a Canon Ixus 70 (SD1000 in America?), if this is any help.

MonkeyChewTobacco · Sep 18, 2009

robertwsimpson said:
usually barreling is less evident at the zoom side of a lens, so zoom in, step back, and take the picture. see if you like that better.

Thanks, Robert

It seems intuitive that it might be better to use the zoom, but I'm really basing that on the geometry of the camera/distance/object. Interesting to see you say the lens itself might make a difference.

Two reasons, then, to step back?

robertwsimpson · Sep 18, 2009

there are sites that analyze lenses for barreling, vignetting, etc, and then post it online, so search for your lens and I'll bet you can find something.

Big Mike · Sep 18, 2009

I don't know if they will be able to find the exactly characteristics of their lens...seeing as it's built into their P&S digi-cam. Those sites usually concentrate on interchangeable lenses.

Another option, if the distortion is too much for you, is just to correct it (as best you can) with software.

robertwsimpson · Sep 18, 2009

oh I assumed we were talking about an SLR here... I shall now take my leave.

KmH · Sep 18, 2009

Shoot fat. Leave plenty of room in the frame between the door edges and the sides of the picture. Then crop to the final image size.

Dwig · Sep 18, 2009

MonkeyChewTobacco said:
Thanks, Mike

I should have mentioned I'll be using a Canon Ixus 70 (SD1000 in America?), if this is any help.

Do some tests.

Most of the modern zooms found on P&S cameras and the kit zooms on DSLRs exhibit a fair amount of rectilinear distortion (straight lines don't stay straight). The amount and type (barrel where the center bows outward and pincushion where the center bows inward) generally varies a good deal with the selected focal length.

The most common pattern is barrel distortion at the wide end and pincushion at the long end. Often there is a sweet spot where rectilinear distortion is very small. This sweet spot is most often a focal length toward the longer end. Take a series of test shots at different focal length ("zoom") settings, varying your shooting distance as necessary, and review the shots to see where the distortion is the least. Then use that zoom setting for your final shots.

Be very very carefult to shoot straight into the door. Any small amount off angle will cause a different type of distortion where the sides of the door, while straight, are not parallel. While this error is fairly easy to correct in Photoshop, its better to get it right in camera.

KmH · Sep 19, 2009

Dwig said:
Be very very carefult to shoot straight into the door. Any small amount off angle will cause a different type of distortion where the sides of the door, while straight, are not parallel. While this error is fairly easy to correct in Photoshop, its better to get it right in camera.

This known as perspective distortion.

MonkeyChewTobacco · Sep 29, 2009

Thanks everyone for your advice.

In the end, things went pretty well. Barrelling/pincushioning proved not to be an issue. I had the camera on a tripod about 6ft (2metres) from the doors with the zoom about two thirds of the way out (sorry - not sure of terminology!).

I processed the images in Paint Shop Pro and found that they were half a degree off level and, on some of the doors, minimally perspective distorted. I could correct these problems easily enough.

An unexpected problem was the variation in the lighting - it was cloudy but the cloud was obviously quite variable in density.

The hardest thing was separating the doors from their background (a white sheet). This needed quite a bit of faffing about with the magic wand tool, the clone tool and the crop tool. But the end product is easily good enough for purpose.