[Leica] 21mm Elmarit (pre-ASPH) vs 21mm SA

[henningw at archiphoto.com (Henning Wulff)]

At 5:53 PM +0800 12/4/04, Alex Fan wrote:
>Hi,  I barely recall that someone has done an excellent comparsion between
>these two lenses, the comparsion has a picture of a building with a
>bicycle near the edge.  The wheel of the bicycle shows the magnitude of
>distortion of the lenses and......
>
>Any idea on where the link is?
>
>Thx
>Alex

I don't know that particular comparison, but I've done comparison of 
these two 21's (as well as many others).

The 21 pre-ASPH Elmarit is a decent lens, and better than almost all 
lenses in this range for SLR's, but it's not up to the level of the 
SA, the current 21 ASPH or the 21/4 VC, except that it has less 
vignetting than the SA. The Elmarit is slightly retrofocus, so that's 
how it gets to show less vignetting, but it also has slightly 
noticeable distortion. Note that this is _linear_ distortion, ie, how 
straight lines at the edges of the image field get reproduced. The SA 
has essentially no distortion, and is the standard in this regard, 
being better than the 21 ASPH in this area alone.

 From the way you phrased your comment, I take it that when you are 
referring to distortion, you mean the way that three-dimensional 
spherical objects are imaged as ovoids in the corners of images made 
with very wide angle lenses. Please be aware that this is not a lens 
fault; in fact, almost all 21mm lenses will cause this same effect, 
unless they have very severe linear distortion. Yes, terrible linear 
distortion will reduce the perspective distortion that causes the 
oblong heads and other spherical objects in photos.

With respect to a bicycle wheel in the corner of an image, if that 
wheel is in a plane parallel to the film, it will be reproduced as a 
perfectly round object (aside from the tire, which will be 
distorted). If it is at an angle to the film plane, it will be 
distorted.

In any case, a bicycle wheel in the corner of an image will tell you 
absolutely nothing about distortion levels in a lens under any 
circumstances unless one of the lenses is an utter dog. No Leica, 
Canon, Nikon, Olympus, etc. lens is.

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    *            Henning J. Wulff
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