[Leica] Intro, now a discussion of MTF

[dorysrus at mindspring.com (Don Dory)]

Frank,
It is not that I find bokeh unimportant for telephoto's, it is just that
for the lenses that I have used, at the distances I use them, the out of
focus areas are so out of focus that it just does not matter.

Typically, I am using a telephoto at or near it's close focus limit so
there is a lot of really out of focus areas.

My experience with telephoto lenses are the same as yours, the 300 and
500 Canon designs are for all reasonable demands diffraction limited.

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 10:22 AM
To: Leica Users Group
Subject: Re: [Leica] Intro, now a discussion of MTF

Hi Don,
I am intrigued that you find boke unimportant in tele lenses. I use 
them a lot for wildlife pictures, and find that boke is crucial, simply 
because the bulk of the frame is often OOF and distracts from the 
subject if the boke is poor. I find boke to be dependant on several 
things. The Canon statement that for good boke meridional (sp) and 
sagital (sp) MTF need to be as close as possible agrees very strongly 
with my experience (where I have seen the MTF curves). OTOH I have a 
Canon macro lens which has boke which gets worse as I focus closer, to 
such an extent it is easily seen in the viewfinder. The sharpest lens I 
own is a Canon 500mm, its boke is also the best I have seen on any 
lens.
Frank

On 2 Jan, 2005, at 14:37, Don Dory wrote:

> 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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