Alley in Pisa, Italy

by Lars Kotthoff

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I just got the Sony DSC-WX9 and DSC-HX100V a couple months ago, and found that, if a person's face is right in the center of the photo (for a photo with 4, 5 people standing, from head to toe), then there is a little distortion of the face (more round). If a person's face is between the center and the right margin of the photo, the distortion is somewhat greater, especially if it is on the WX9. When the person face is near the right margin of the photo, the distortion is a lot, almost making the face 20% wider.

I noticed some distortion on the Canon cameras as well, such as the Canon SD600. On the SD600, it seems that people's face are pulled somewhat longer, so it does compensate a little for people's face usually looking more round on a camera. (people's face became rounder and then pulled longer, so it seems to be slim as a final result).

I also used a Canon Rebel T2i with a Canon 50mm lens (probably the Canon EF 50mm f/1.8 lens that's about $120 on Amazon.com), and there was some distortion as well. Are there some medium priced camera / lens that can produce photos with very very little distortion? The price might be $150 up to at most $800.

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Are you OK with using a prime (i.e. non-zoom) lens? In what kind of focal length range? –  James Youngman Apr 8 '12 at 7:41
    
can you show us some examples of this distortion? –  Paul Cezanne Apr 8 '12 at 12:24
    
does the Canon 50mm f/1.2 make a big difference from f/1.8? The price is 13x of that of f/1.8 ($1600 vs $120) –  動靜能量 Apr 8 '12 at 17:42

2 Answers 2

I'm quite surprised you notice the image distortion with the 50mm lens. Prime lenses in that focal length range generally have minimal distortion, usually around 0.5%. However, macro lenses usually have low levels of distortion. I took a quick look at the DXOmark website for you and found that Canon make a 60mm macro lens which has only 0.1% distortion; see http://www.dxomark.com/index.php/Lenses/Camera-Lens-Database/Canon/EF-S-60mm-f2.8-Macro-USM/(camera)/619/(cameraname)/CANON-EOS-7D

However, this focal length may not be convenient for group shots or full-length portraits (which are the uses you actually mentioned). I didn't spot a wider lens with low distortion.

The Canon 24mm TS-E lens almost certainly has even lower distortion (Tilt/Shift lenses are used in architecture photography, where distortion is a big deal, and if a T/S lens does have distortion, it's hard to correct for it in post if movements were used). However, I think all the Canon TS lenses are beyond the price range you specified.

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I think the distortion you are seeing is not caused by the lens, I think it's just perspective distortion.

The Canon 50mm f/1.8 has a DXOmark distortion rating of 0.2% and if you look at the actual measurements, especially the grid you will see that the distortion is very low - too low to notice in a normal picture - I don't know about the other cameras you listed but I suspect it's also not the camera's fault at all.

Perspective distortion is caused when the subject is not completely parallel to the camera's sensor plane - for example, if you take a wall (so the subject is flat) and shoot up you will see the top of the wall is narrower than the bottom, shoot down or to the side and the areas farther from the camera will look smaller.

Shoot this wall when the wall is parallel to the camera you get a boring but relatively distortion free image.

When you photograph people there's another complication - people are not flat - so different parts of the person will be at different distance from the camera.

To see this effect just take a picture of someone's face from as close as possible - the nose will be huge because it's relatively much closer to the camera than the rest of the face, take the same picture from far away and the person looks nice again.

So, what should you do to reduce distortion:

  1. Hold your camera so that it's completely strait, don't tilt it up or down (for full length portraits that means not holding the camera at eye level), you may want a tripod and/or a bubble level.

  2. Also, when you are taking a picture of a group arrange them so they are the same distance from the camera's sensor plane (as much as possible) and point the camera at the center of the group.

  3. Get as far as you possible can from your subject so the difference distance between parts of the subject(s) are very small compared to distance from camera.

  4. Zoom lenses (and point and shoots) do have distortion, usually there's more distortion near the ends of the zoom range (most zoomed in and most zoomed out) and less distortion near the middle of the zoom range - but you have to test your actual camera/lens to see where the "sweet spot" is.

"Normal primes" like the 50mm f/1.8 don't have that problem, but very wide lenses (even prime lenses) do have quite a bit of distortion.

A Canon T2i with the 50mm f/1.8 (or the the equivalent modal from any of the other companies) is actually a very good choice if you follow the rules because the 50mm has very little distortion (less than any point and shoot) and the 50mm field of view on an APS-C camera will force you to get far away so you can get 4-5 people in the frame (a longer prime lens will be even better but much more expensive)

Of course, getting far away from your subjects then setting up a camera on a tripod and leveling it is much more work than just snapping a picture - so it may be better to just live with a little bit of distortion.

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