[rollei_list] Re: Lens "look" of Triotar? - Rollei B35 40mm f3.5 variant
- From: "John Wild" <JWild@xxxxxxxxxxxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Fri, 12 Jan 2007 08:28:00 -0000
Thanks Richard, that's very interesting. I don't know anything about
lens construction except for what I learnt in physics at school about
'bending' of light rays as they pass from air to glass and 'vikkyverky'
but I have picked up some useful information from this listing, so my
knowledge is getting better. :-))
John
-----Original Message-----
From: rollei_list-bounce@xxxxxxxxxxxxx
[mailto:rollei_list-bounce@xxxxxxxxxxxxx] On Behalf Of Richard Knoppow
Sent: 11 January 2007 21:45
To: rollei_list@xxxxxxxxxxxxx
Subject: [rollei_list] Re: Lens "look" of Triotar? - Rollei B35 40mm
f3.5 variant
John
Triotar is a name used by Zeiss for Triplet type lenses.
There are probably many variations of design sold under the name so
performance may not be consistent. In general a Triplet has just enough
degrees of freedom (powers, spacings, curvatures) to allow correction of
all seven of the basic lens aberrations. Other types, with more degrees
of freedom, allow better correction of secondary aberrations. A Triplet
can be quite good if not too fast or wide angle. I don't have a Rollei
with a Triotar but have some other Triplet lenses, including a 12"
Rodenstock lens for L-F. The Rodenstock lens is NOT a soft focus lens.
The spherical aberration is quite well corrected so its sharp in the
center even wide open (f/6.3) but needs to be stopped down to get the
margins sharp. It will illuminate an 8x10 film but is limited to 5x7 for
good corner sharpness.
The curious thing is that, according to Kingslake, Triplet lenses are
not cheap to make because they are very sensitive to element spacing
requiring precision mountings.
Probably this was less than the cost of the additional element and
cementing required for a Tessar. In general, a Tessar will have a wider
field for a given f/stop than a Triplet of the same speed and focal
length.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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