Re: [Leica] 21 or 24 mm M lens: advice sought

[Dennis Painter <dpainter@bigfoot.com>]

Mark Rabiner wrote:
> 
<snip>
> In rereading Erwin's pages on the 21s he does not specifically address
> the distortion issue with the ASPH as he does with the other 21's as a
> word "distortion". He says all aspects of the lens are vastly better. He
> says: "Astigmatism and curvature of field are almost fully corrected"
> which are distortion issues I should think.

Astigmatism and curvature of field are not distortion.  Think of
astigmatism error as a failure to correctly image a single point in the
subject as a single point on the film.

Curvature of field is failing to bring all points of a flat surface into
flat focus at the film plane. The focus field at the film plane is
curved, hence the name.

The 21 SA and 21 ASPH are both great performers. The SA having the
disadvantage of not metering on the M6, the ASPG having the disadvantage
of greater depletion of the bank account.  If you can afford it I would
say get the ASPH.

Dennis


> But he doesn't specially say
> better corrected than the SA. People should read this themselves to make
> sure my comprehension agrees with theirs.
> I had asked the tech rep at Leica if the new 21 or the SA were "true"
> wide angle lenses like the Biogon and view camera lenses and thus
> possessing their intrinsic lack of distortion which you describe here so
> excellently. His answers were relational and I was confused and not
> perhaps absorbing important points. Your present response clarifies some
> of that now.
<snip> 
> Mark Rabiner