Archived posting to the Leica Users Group, 2007/01/11
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>On Jan 11, 2007, at 6:23 PM, Len wrote:
>
>>Thanks. I have the use of it (Telyt 560/f6.8) for the weekend along
>>with a R8 body. I
>>still find it hard to believe a simple 2 element lens can be that good.
>
>I have a friend, a professor of optical physics, at the University
>of Rochester who insists that the sharpest long focal lenses have
>the fewest elements. The Telyt lens only covers a field of 3.5
>degrees on a 35mm frame, 4.5 degrees on an M8 frame.
Hi Larry,
I think you might have the two angles mixed. :-)
But it is a very good lens. Due to this, the 560 is actually somewhat
better, or rather of more even performance than the 400.
The sharpest long focus lenses would be those of limited elements,
such as the 3 element 800/6.3 that used the most appropriate glasses.
The 400 and 560/6.8 Telyts used special, newly developed glasses, but
not that exotic in today's terms. The 800 unfortunately was pretty
much unaffordable. It certainly had better performance than the even
much more expensive and also very complicated 1200/5.6 Canon EF.
>With that narrow a field you don't need to worry about all the
>aberrations that multiple elements are required to correct. In fact,
>if you used a narrow band pass filter, a single element lens would
>be almost ideal.
A bit tough on colour photography, which the narrow angle achromat is
very good at otherwise.
>Obviously Leitz engineers agreed and the results confirm the theory.
>We need the multiple element ASPH designs because we insist on short
>focal length fast lenses for multicolored subjects at close ranges.
>
>The 42" Yerkes telescope, the biggest refractor telescope in the
>world is a two element achromatic.
>
>Larry Z
>
>
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* Henning J. Wulff
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