[Leica] Intro, now a discussion of MTF

[dorysrus at mindspring.com (Don Dory)]

Frank,

I concur that calculated MTF's are almost a waste of time for a
consumer.  Obviously, for the design engineer, it is a very powerful
tool as the design is massaged to completion

The center of the image circle is relatively unimportant as all lenses
will do very well assuming no de-centering of elements.  That's why when
looking at an MTF chart I start looking at the area off center; if the
lines start to drop and the T and S lines start to diverge then the lens
will not be so good.

You are correct about flare, for that you do need some test shots, or a
really well designed hood. :)  I think also that the family history of
the lens line is also important.  My recent Leica and Zeiss glass is
mostly flare free in some pretty severe lighting situations, but some of
my newer Canon and Nikon glass is not so good.  I think that the
engineering rules in different design groups have different priorities.

As to bokeh, as I think a previous poster was largely correct that bokeh
is a combination of diaphragm blade design, under corrected spherical
aberration, and a modest amount of astigmatism.  Especially for modern
aspheric designs I think that the transition to out of focus will be
rapid and somewhat random causing some strange artifacts. Of course,
with a telephoto lens, bokeh becomes largely irrelevant.

Also, as we move to lenses designed for smaller sensors, controlling
depth of field will become more interesting. 

0.02

Don
dorysrus@mindspring.com 

-----Original Message-----
From: lug-bounces+dorysrus=mindspring.com@leica-users.org
[mailto:lug-bounces+dorysrus=mindspring.com@leica-users.org] On Behalf
Of Frank Dernie
Sent: Sunday, January 02, 2005 3:52 AM
To: Leica Users Group
Subject: Re: [Leica] Intro

Don,
The publication of measured MTF would help, calculated does not IME. I 
have tested two lenses, one a multi element zoom, another a prime. The 
zoom has better (calculated) MTF in the centre of the frame than the 
prime, but the prime is clearly superior on photographs. I expect there 
is a MUCH greater variability in multi element lenses simply because of 
the problem of manufacturing them all the same!
OTOH MTF tells nothing about flare resistance or boke, both more 
important than ultimate resolution on the type of photography I do (I 
rarely use a tripod and never higher resolution film than Kodachrome 
and am now using digital)
Frank

On 2 Jan, 2005, at 03:53, Don Dory wrote:

> Jeffery,
> There is, it is called a MTF chart.  While every machine is different,
> if a lens is transmitting 60% contrast at the 30 or 40 cycle line out
> 15mm wide open then you have a really good lens.
>
> If every manufacturer would just publish MTF charts for real
production
> lenses then most of the nonsense about my lens is better than your
lens
> houey would stop.
>
> 0.02
>
> Don
> dorysrus@mindspring.com

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