[LRflex] Re: Optimal Focal Lengths ... for Dave Simms
- From: David Simms <simmszee@xxxxxxxx>
- To: leicareflex@xxxxxxxxxxxxx
- Date: Sun, 1 Aug 2010 12:06:44 -0700 (PDT)
Walter's link, with the Putt's article on the 80-200 zoom definitely puts that
lens in the exceptional class.
In order to support my former contention that certain focal lengths are
"sweeter" than others, I offer this quote from Putts.
"Leica lenses at the fixed focal length of 135 mm have vanished for a long
time,
but it still is a very interesting focal length where exacting performance may
be required. And around 200 mm current prime lenses are outstandingly good and
it is reasonable that the photographer expects the same type of performance of
the vario lens at this focal length of 180 mm to 200 mm."
I don't know what he means by "vanished" but i would guess that he means that
everything that can, or could, be done designwise, with the 135mm focal length,
has been done and that, insofar as the designer is concerned, the book is
closed.
Dave
________________________________
From: David Young <dsy@xxxxxxxxxxxxxxx>
To: leicareflex@xxxxxxxxxxxxx
Sent: Sat, July 31, 2010 8:28:17 AM
Subject: [LRflex] Optimal Focal Lengths ... for Dave Simms
Good Morning, Dave!
You wrote:
>According to the tests and commentaries, it's hard to find a Leica zoom that
>isn't the equal of a prime lens.
This may be true of the current crop, but certainly not of the
earlier, Minolta designed, Leica Zooms.
>I sometimes wonder whether, when a manufacturer
>is locked into producing,say, a 50mm lens because it is deemed to have a
>"normal" perspective, that they don't handicap themselves.
>What I'm thinking is that, when all the calculations have been done,
>a 44.3 mm
>lens may end up being optimal, or, a 31.2mm for example. In other
>words, there
>must be particular focal lengths that are optimal, in terms of design
>parameters, whereas it's a struggle to produce the "standard" focal lengths.
>Hence, when stacked against this inherent uphill battle, it may be able to
>produce a relatively good zoom which may never improve upon "optimal" focal
>lengths but which knocks the hell out of the standard ones.
Back in 2006, I had a discussion with Peter Karbe, head of the
optical dept, at Leica. He told me that there are two factors at
play, when it comes to lens design... the designer's skill and the
company's money.
Although modern computerized ray-tracing and related software really
speeds up the optical design process, it does not replace the
brilliance (or lack thereof) of both the optical and mechanical
designers. The designer can simply try different lens shapes and
glass types much faster. As well, some glass types can cost a
thousand Euros per kilo, while basic optical (flint) glass may be as
low as 10 to 15 Euros/kilo. So while some designers may be free to
use the best glass for the purpose, most often the Sales department
puts restrictions on what can be used by limiting the cost of
production before design is even started!
Then there is the complexity of the mechanical design.... in
virtually all zooms, different internal "blocks" of elements move at
different rates, and different distances, not to mention different
directions, to achieve optimal performance. Here again, having more
groups that move independently may well improve performance, but it
also makes the lenses much more complex (read: expensive) to
manufacture. So, once again, the Sales department is often an
impediment to the design.
So, you see, it has little to do with "optimal focal lengths", and
much more to do with final production costs.
Because prime lenses are far simpler, mechanically, at any given
price point, any firm can put more into the design, as the mechanical
construction portion of the final price is quite low. Besides, a
good prime lens may have only 5 to 8 elements. Fewer elements means
not only fewer reflections and other internal problems, but also
lower costs, as you simply make fewer pieces! Here, performance for
the dollar is generally highest.
Zoom lenses often have between 12 and 18 elements... add in the more
complex mechanical movements and you can see where/how costs rise.
Thus, to keep retail prices "reasonable", most makers limit
manufacturing costs before design begins. Ergo, very few zooms equal
the performance of top notch primes.
I think Leica zooms do better simply because of the price range they
are in. Leica allows more to work with. As well, Leica design their
lenses for top-notch performance, and only after the design is done,
do they evaluate whether they can afford to produce it. I was told
that there are many designs which never see "the light of day", for
even Leica cannot afford to produce them at a sellable price!
And I'll still put my 80-200/f4 up against any prime, from any
maker. Something that can be said of very few zoom lenses.
Cheers!
-------------
David Young - Photographer
Logan Lake, BC, Canada
Wildlife & Sports: www.furnfeather.net
Personal pages: www.main.furnfeather.net
A micro-lender through KIVA.org.
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