[pure-silver] Re: (slightly) OT MF equipment dilemma
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 19 May 2005 21:53:49 -0700
----- Original Message -----
From: "Randy Stewart" <randal@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, May 19, 2005 7:21 PM
Subject: [pure-silver] Re: (slightly) OT MF equipment
dilemma
>
> ----- Original Message -----
> From: "Ryuji Suzuki" <rs@xxxxxxxxxxxxxxx>
> To: <pure-silver@xxxxxxxxxxxxx>
> Sent: Thursday, May 19, 2005 10:42 AM
> Subject: [pure-silver] Re: (slightly) OT MF equipment
> dilemma
>
>
>> From: "Stefan Kahlert" <s.kahlert@xxxxxxxxxxxxx>
>> Subject: [pure-silver] Re: (slightly) OT MF equipment
>> dilemma
>> Date: Thu, 19 May 2005 19:06:44 +0200
>>
>> > The Autocord is an exception where the film travels
>> > from the upper
>> > chamber to the lower chamber which means that only the
>> > film already
>> > exposed gets bend.
>>
>> That's better, though I'm not sure how much does that
>> help to the
>> flatness.
>
> It makes a considerable difference, if you leave a partly
> shot roll of film
> in the camera for any length of time.
>
>> By the way, was any of the Autocord made with 6-element
>> optics? (AFAIK Yashica and Minolta TLRs are all triplets
>> or Tessar's.)
>
> No, early Yashica TLRs, pre-Yashica 12, were mostly
> triplets, and later
> models were 4 element Tessar types, although testing
> indicated that they
> were generally inferior to true Tessars or the similar
> Rokkor [Teeser type]
> in the Autocord. All Minolta Autocords use a very nice 4
> element design,
> but no 6 element. A few of the low volume Japanese TLRs
> used 5 element
> designs which are said to be very good. [Koniflex;
> Airesflex with the Nikon
> contributed Nikkor lens set.]
>
>
I wonder what you mean by "true" Tessar. If one having
the right to bear the name that makes it either Zeiss or
Bausch and Lomb, who had a license (sort of) for the name.
However, Tessar is a generally recognized name for a generic
lens type although there is quite a bit of variation among
lenses dubbed Tessar types. The conventional Tessar has four
elements with two cemented together at the rear. In Paul
Rudolph's original Tessar the front cell had two airspaced
elements of "old" glass, the rear two cemented elements of
new or "Jena" glass. The cemented surface of the rear group
serves to correct zonal spherical, oblique spherical, and
reduce astigmatism. In the Tessar the front group has low,
negative power, the rear group having most of the power and
most of the corrections. Tessars vary all over the place in
performance. The generic type is capable of excellent
performance if not made too fast but that cability is not
always achieved; it depends on the skill of the designer and
the lens maker. Tessars on the oustanding side are the Kodak
Commercial Ektar, a series of f/6.3 lenses made during the
mid 1940's to 1960's partly to promote the use of color
film. These lenses are extremely sharp and nearly
apochromatic. Other lenses of this type do not necessarily
come up to this standard. The Tessar and Xenar lenses on
Rolleiflexes appear to be close to the limit of performance.
At f/2.8, the Tessar can be a satisfactory, but never
outstanding design. One limitation of the Tessar is oblique
spherical aberration. It can be reduced to acceptable levels
but is one of the factors limiting the speed and coverage
angle of the lens and other generic types are more
inherently free of it.
Some variations of the Tessar include: reversal of the
order of power in the cemented rear component. This was done
by Kodak in the Kodak Anastigmat Special, a front element
focusing lens. According to George Aklin of Kodak, this
arrangement has an advantage when high index glass is used.
Another variation is the position of the stop. In the
conventional Tessar the stop is in the rear air space. In
the Leitz Elmar it is in the front air space. I don't know
what advantage, if any, this had. It is also possible to
have a reversed Tessar with the cemented component in the
front. There have also been occasional designs with three
cemented elements in the rear, the Ross Xpress is an
example. Some variations evidently were for the sole purpose
of getting around a patent.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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