Full frame vs APS-C: distortion & bad lens copies

-- "Reasons being severe distortion"

Can you supply a sample image showing your problem.

The point is, there are several different kinds of distortion, and not for all the lens is to blame.

- barrel distortion. This is caused by the lens.

- perspective distortion. This is caused by the user.

- Border distortion of rectilinear corrected lenses (usually only seen with UWA lenses). This kind of distortion is necessary to keep straight lines straight. To reach this goal, areas have to be streched the more you get to the corner. This is caused by design.

The latter two will not go away if you go FF.

For the barrel distortion ... photozone reports -1.25% for the 10-22 at 10mm and -2.47% for the 17-40 at 17mm. Both are measured on APS-C ... but since barrel distortion will not get better when using FF, you can expect at least the -2.47% on FF also. So the 10-22 on APS-C would be better here.

If distortion (barrel, moustache or pincushion) is a concern then you should process your images with PTLens software that will deal with it (and also correct for CA and vignetting). That might leave you a lot happier with your lenses, and be cheaper than trying to pursue an impossible Holy Grail.

http://epaperpress.com/ptlens/

Wide abd ultra-wide angle lenses produce a characteristic FOV which, requires a lot of care when framing. Tilting the camera and/or using off-center subjects, etc... can cause unwanted results. Some lenses have better performance than others with regards to correcting certain issues inherent to those lens designs.

If you want the best ultra wide primes and/or zooms, you have to spend like there is no tomorrow so, can't have it both ways. IF you want to save you have to be wiling to accept a level of compromise in performance.

But, unless you want to use an anamorphic system (!), that's the way ultra-wides work.

PT Lens works as do other techniques but, remember...you are stretching pixels so, even then there is a limit to what can be done without unwanted results.

I know this is a stupid question, and I will probably kick myself for not figuring out the acronym, but what is "CA"?

CA is Chromatic Aberration:

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

The 17-40 will show distortion on a 5D at the 17mm focal length, which means that you may not get completely straight horizons in a landscape image. DPP will fix that but you will loose a small amount of the image in the process. Distortion at 24mm is far less. (I know the difference between real distortion a prospective distortion)

While there are certainly bad equipment out there and I have found lenses that I did not like as much as others, but if you look hard enough for defects, you will likely find them in practically any piece of equipment.

Distortion of any type (barreling/pincushioning or perspective) is easy to correct with just about any photoediting package (e.g. Photoshop). However, if distortion is your primary concern, you might consider the Sigma 12-24 a an ultrawide. It won't give you the sharpness and contrast of, say, a 17-40L, nor will it control CA as well. There are also quality control issues, so you might not get a great copy. However, the lens does a phenomenal job of staying flat and true, with nearly zero barreling or pincushioning. It's also the widest angle rectilinear zoom ever engineered (wider than the 10-22 zooms because it can be used on a full frame). It's tied with the Voigtlander 12mm prime, which of course is only suited for a rangefinder. I rather like mine. It's a little engineering miracle, and you can't beat it for interior architectural work.

When people write about "distortion" on wide angle lenses they may be referring to a number of different issues, and the answer to your questions will be quite different depending upon what _you_ mean by this.

By their nature wide angle lenses create perspective distortion - any wide angle will do this, from the cheapest to the most expensive. This is the quality responsible for things like buildings tilting inwards, large noses on people you photograph close up, and so forth.

All lenses exhibit some barrel (outward bulging) and/or pincushion (inward bending) distortion and wide angle lenses can be especially prone to this - and it can be confused with the normal perspective distortion.

Wides tend to be perhaps more prone to "chromatic aberration" - color separation around high contrast areas most often in the corners of the frame. For example, the edge of a building or branches might have red/green lines around them.

Corner light fall-off (or "vignetting") is also found on virtually all lenses at their largest apertures, though it generally diminishes to insignificance as you stop down.

Corner softness - noticeable blurring in the far corners of the frame - afflicts many wide angle lenses, especially when shot at focal length extremes and wide open. This also diminishes as you stop down the aperture.

It is very important to understand what you mean by "distortion" for several reasons. First, it is quite possible that what you are seeing is simply the normal behavior of all lenses - e.g. corner fall-off and/or softness at large apertures. Trying to "fix" this by buying more lenses could be fruitless. Second, It could be a "problem" that simply requires a change in shooting technique rather than new gear. Third, some "distortion" can easily be fixed in post-processing, chromatic aberration for example. Fourth, if it is a "hardware problem" with the particular lenses you have used, it is critical to know what the issue is so that you can decide what lenses might improve this.

Dan

I'm refering to the "stretched out" look at the edges edges, the type that renders a normal car into a limo and makes cartoon heads of portraits..