[rollei_list] Re: Sharpness and Old Tessars --not lynching or the Doc
- From: Jerry Lehrer <jerryleh@xxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 19 Oct 2005 18:23:31 -0700
Richard,
Kodak also made a few Ektars and Kodak Anastigmats in the
aperture of f7.7 in a few focal lengths. I use one of them in a
Nikon bellows for a few applications. It is amazing for such an
ancient lens! It is 6" FL
Do you have any knowledge of this series of lenses?
Jerry
Richard Knoppow wrote:
> Lots-O-Snipping........
>
> My comparison was among three lenses of the same speed
> and focal length, namely the Kodak Ektar, f/4.5, Zeiss
> Tessar, f/4.5, Wollensak Raptar f/4.5. All of these were
> used on Speed Graphics at one time or another. I have a
> couple of each. The best performer is the Ektar. It has
> minimum residual spherical and generally is the sharpest.
> These Ektars vary in age from 1941 to 1952. The next is the
> Zeiss Tessar. Mine were made in the late 1930's. The Raptars
> were probably made in the late 1940s, I have no Wollensak
> serial number info. The Tessars must be stopped down a
> little to be sharp in the center and have enough focus shift
> to be a factor in setting up a rangefinder. The Ektars, with
> one exception, have virtually none. The exception is a very
> early (1941) 101mm lens but I also have a 127mm Ektar of the
> same date which has no focus shift.
> The Raptars (135mm and 101mm) are sharp in the center and
> seem to be well corrected for spherical aberration but have
> something else wrong with them. This looks like coma but may
> be something that mimics it. The effect is to smear out the
> margins of the image. Even at f/32 there is just a little of
> whatever this is left. I have checked several Raptars and
> they all have this problem which leads me to think its a
> design blunder rather than manufacturing error. The
> Enlarging Raptar of the same vintage also seems to have
> problems. Since the Optar is the same lens with the Graflex
> house name on it they are the same. I don't know how such a
> poor design could have escaped notice. Graflex changed
> vendors for the Optar to Rodenstock after a few years.
> Not all Wollensak lenses are poor. The Tele-Raptar also
> sold as the Tele-Optar is a very good lens and evidently
> many of their pre-war lenses were good.
> The biggest difference between the f/4.5 and f/6.3 Tessar
> seems to be coverage which is a little larger for the slower
> lens.
> In general slower lenses are easier to correct than faster
> ones simply because the steepness of the rays inside the
> lens and amount of surface curvature are less. High index
> glass helps because it reduces the amount of surface
> curvature needed for a given power. In the past the
> dispersion of high index glass was too high making chromatic
> correction difficult or impossible but modern glass,
> beginning with the rare earth glasses, offer high index
> glass with much lower dispersion than the older types. I
> don't think any rare earth glass was used in the Ektar
> series based on the Tessar (there were lots of other generic
> designs sold under the name) but Kodak certainly had it
> available.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
> ---
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