[rollei_list] Re: Sharpness and Old Tessars --not lynching or the Doc
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Wed, 19 Oct 2005 13:44:37 -0700
----- Original Message -----
From: "Eric Goldstein" <egoldste@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Wednesday, October 19, 2005 7:59 AM
Subject: [rollei_list] Re: Sharpness and Old Tessars --not
lynching or the Doc
Richard Knoppow wrote (snipped):
Tessars, as a generic type, are capable of excellent
performance but, of course there are better and worse
designed lenses. An example of a very well designed
Tessar type is the series of f/6.8 Commercial Ektar
lenses. The f/4.5 Ektars made for press and medium
format cameras is nearly as good. Zeiss Tessars from the
1930s and '40s are very good lenses but not quite up to
the Kodak lenses, perhaps because of the glass available
at the time.
I'd bet you a nickel that it is more a function of speed.
As I mentioned, this is a medium speed design, which is
probably why modern shooters eschew it. The large format
Nikkor f/9 series is an excellent tessar type, and as you
say so was the Commercial Ektar f/6.8 series. It stands to
reason that the MF f/4.5 Ektars should outperform the
f/3.5 Zeisses (all things being equal) as they are more
within the optimal design paramaters of the basic lens
type. Greenleaf puts the optimal design speed of a
tessar-type of 100 mm FL at f/6.3.
Eric Goldstein
---
It is partly a matter of speed. For equally well
designed lenses the slower ones will perform better than the
faster ones because the angle of the rim rays is less.
However, even when comparing lenses of he same speed there
can be a variation in performance due to something in the
design. For instance, f/4.5 Kodak Ektar, about a 1940
design, have less spherical aberration wide open than the
Zeiss Tessars of the same period. A much later design (about
1946), the Wollensak Raptar, also sold as the Graflex Optar,
has a design error of some sort. These f/4.5 lenses seem to
have excessive coma, or perhaps its oblique spherical, which
is consistent with all focal lengths. These lenses have a
little smearing at the corners even at f/22 where the Kodak
and Zeiss lenses are free of it by f/8. I will have to look
at Greenleaf again but I think what he says is that f/6.3
Tessars are better than f/4.5 rather than it being an
optimum speed. At f/8 the lens is even better which is why
Zeiss Tessar type process lenses are around this speed and
why the Nikkor lens is so good.
BTW, it sure would be intresting to know what Greenleaf
really thought about various manufacturers, he hints in this
book and in a couple of articles he wrote that most QC was
pretty awful. I don't think the Goerz Dogmar on the dust
jacket is a coincidence, reading between the lines I think
he had a high opinion of Goerz.
I typed f/6.8 in error for the Commercial Ektar, they
are f/6.3. Zeiss and B&L also made a series of Tessars of
this speed. I've never had one to inspect but the published
specs indicate it has a slightly wider coverage than the
faster versions.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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