Correcting barrel distortion

[ExclamPt]

I just acquired a digital camera and have been doing a little research into eliminating the barrel distortion which is sometimes apparent, especially when using the wideangle setting of the zoom.

I can recommend PTLens, a freeware frontend to Panorama Tools. It makes correction easy, using a database of camera parameters and embedded EXIF data for the corrections. Also, multiple images can be corrected at one time.

Check it out at

http://epaperpress.com/ptlens/index.html

[brandonx49]

Good Post - I was wondering what that is called. Is this a common problem with digital cameras? Something to give more attention when I get a camera.

Brad

[ExclamPt]

Brandon,

Yes, it's common with digital cameras, although any "reverse telephoto" wideangle design can exhibit it. It's common also with zoom lenses at certain settings.

But some lenses are purposefully designed to accentuate it. I suppose the 180 degree fisheye is the classic example.

Purple fringing, especially near the edges of a photo along high contrast boundaries is also common with digital cameras.

Digital camera reviews almost always talk about the extent of these two aberrations in the camera under discussion. The camera I just bought supposedly has less than average fringing and barrel distortions than others of its type. But both of these aberrations can be noticeable under certain cirumstances.

Panoramic Tools claims it can also reduce purple fringing by shifting the pixels of the separate color channels different amounts. I have yet to try this.

[Rexx]

Hi,

Small clarification here. Barrel distortion is an optical phenomenon, and has nothing whatsoever to do with digital. However, all distortions are products of lens design compromises. In a zoom lens with a wide range compromises are more and bigger than in a fixed lens or a zoom with a shorter range. There are quite a few digital cameras out there with zooms in the 10x range (and even a Panasonic with a 12x zoom), and this will account for digital cameras displaying more optical artefacts than we are used to from analogue.

A few optical artefacts are actually based on digital technology. These are "blooming" and "purple fringing" (as opposed to chromatic aberration), which are produced by the micro lenses layered on top of the image sensor.

[ExclamPt]

I defer to Rexx's obvious expertise in this area.

Back when I was a practicing photojournalist, the common wisdom was to avoid zoom lenses altogether, and go with well-designed fixed focal lengths. This is usually not an option with the common consumer digital camera which does not have interchangable lenses. Also, the best lenses employ aspherical elements and rare earth glass, two expensive additions not usually found in consumer level cameras.

In any case, lens design is often a compromise of expense and performance. One lens may perform best when focused at 10 meters, another at 1 meter, for example.

Many consumers have "megapixel lust." The more pixels, the better they reason. Obviously, though, the number of pixels is only one consideration when determining image quality.

This is a complex subject (or can be). Rexx is obviously well-schooled.

So...what he said.

[Rexx]

Two good examples here are from the current crop of 8 Mpix (sigh) cameras. The more or less agreed-upon winner in image quality is the Olympus C8080. But it has only a 5x zoom, less than any of the other four. Consequently it is natural to assume the Olympus engineers have had to make the fewest compromises.

Another example of what ExclamPt mentions is the Sony F828, which has a "sweet spot" somewhere around the middle of the zoom range, where it shoots phenomenal pictures, but then comes up with quite disappointing results near the ends of the zoom range.

So there are no hard and fast answers, except there are lots of compromises, and you have to decide which ones are the least disturbing to you. Whatever anyone says, the perfect camera does not exist.

Hmmm, this really ended up being for brandonx49. Hope you don't mind, ExclamPt. I am afraid I turned out rather rude Really sorry about that!

Hey, you're an ex-IBM'er! Why do you think my nick is Rexx?

What camera did you buy?

[ExclamPt]

Rexx,

You were not rude at all.

Yes, I'm an ex-IBMer. But I only worked for them a short time after I (and many others) were traded in a deal between Monsanto's and IBM'S CEO's. It was just like being a major league ballplayer, without the salary.

Before being a systems programmer, though, I was a photojournalist until I realized eating would be a good thing.

And thanks for your input, Rexx!

BTW, I just bought a Canon S45. I already had a Canon G3 but wanted something small to fit in my pocket. These are in addition to SLR's, a viewcamera, stereo cameras, etc. Boy, I've spent a bunch on this hobby!

[Rexx]

A view camera??!!??

I've learnt from The Luminous Landscape that Real Men photograph with a view camera. I've used SLR for 30 years, but I haven't even seen a view camera! I'm not worthy of formatting your CF card!

[ExclamPt]

The view camera is nothing Ansel Adams would use, but it's a conversation piece.

Years ago, when I had a minimum wage job in an acrylics factory, my boss let me spend my spare time constructing the camera in clear and black Lucite. I had plans for the camera in wood, but plastic seemed cool at the time. I think they still sell similar kits in cherry wood.

A friend of mine gave me a lens, and voila!...view camera.

Now if I had a 4x5 enlarger!

[Rexx]

Wow!

Sorry, my vocabulary fails me.

That is some conversation piece alright!

If you're serious about the 4x5, you will get excellent results with a scanner you know. My Epson Perfection 2450 came with an assortment of plastic frames to hold the most usual and unusual negative formats. The Epson doc talks about scanners with manual focusing. Mine hasn't, but I take this as a hint that high-end Epsons may have.