[Leica] Eric's comments on "normal lenses"

[Frank.Dernie at btinternet.com (Frank Dernie)]

MPFJI - perhaps you have already mentioned this - but are you referring 
to the performance at larger apertures? A look at the MTF curve on any 
fast lens will find substantial loss of performance at wide apertures 
and even more so at the edges. Whilst Leica lenses may be sharper wide 
open than most this is still the case. I can't lay my hands on the MTF 
curves of the Leica 50s at the moment or I would quote magnitude. Even 
at the centre the sharpness will be much less open than stopped down 
and the edges and corners much worse. Curvature of field is a feature 
of many lens types and other aberrations are usually corrected in 
priority over this in all lenses except macro lenses. M lenses are 
reported to be designed to be more balanced for curvature of field 
because of the focussing method.
I have never been inconvenienced by this personally because for 
landscapes I am stopped down for DOF anyway and the sharpness of the 
edges and corners is usually massively improved by stopping down, for 
wide open shots I expect only a part to be in focus, usually near the 
center, and the DOF is so small that the small area in focus at the 
edges not being in the same plane as the focussed main subject has 
never been a problem for me.
Frank

On 4 May, 2004, at 21:09, Robert Palmieri wrote:

> Eric -
>
> Thanks for spelling out your take on this.  However...
>
> I was referring to the horozontal field of view (in "landscape" mode)
> not the diagonal, which seems pretty meaningless to me....
>
> The center-to-edge lack of sharpness when focussed at infinity is a 
> fact
> with my lens, as shown under a 30x magnifier.  Whether this is indeed
> due to actual field curvature I kinda doubt, but as I understand it
> field curvature problems don't just get lost in the DOF when focussed 
> at
> infinity.  And this lens is indeed reputed to be rather affected in 
> this
> department, while the 50 Summicrons are not.
>
> I'll post some snaps later in the week, mostly of examples of the
> collapsible and 'lux doing what they do best.  If I can find a slide of
> the Lux center vs. edge thing, I'll scan it also.
>
> Bob Palmieri
>
>
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