Lens question please_Gundlach, Turner-Reich series II No. 1

"____" wrote in message
...
In article , jjs
wrote:

"AAvK" wrote in message
...

What about for mono films? I think because of this
problem I
would never use this lens for color films!

I took it that Richard was addressing B&W. If aberation
occurs in a
particular color for which the film is sensitive, a
correcting filter will
help.

Black & White film is sensitive to color (obviously) and
not equally
sensitive to all colors. Filters are important.

In my early day of LF photography

I once bought an ARTAR that was supposed to be a good lens
and covered
8x10, it sucked royally for B&W all kinds of ghosting on
b&w even when
pointed 180 degrees away from the sun on a cloudy day. The
******* I
bought from extracted a 50 dollar restock fee out the 350
dollar check I
bought with even after I had to pester him for about 3
months to refund
my money.

I can think of only one nice thing to say about him:
Cocks---er, may he
rest in pieces.

--
The Apo Artar is a four element air spaced lens with
eight glass-air surfaces. It does have some flare but should
not have bad ghost images. I have two, one a very old
uncoated lens from the 1920's. Its very sharp and has good
contrast. The other is from the 1960's and is coated so it
has little flare.
Note that while both flare and ghost images come from
internal reflections and are helped by coating they are not
quite the same. Most flare is in the form of an overall
diffuse field of light all over the image while ghost images
are fairly sharp, or at least recognizable, images in the
image field of bright objects either in the image or just
outside of it. Ghosting is usuallyu due to the design of the
lens rather than just having glass-air surfaces. Both flare
and ghosting can also be cause by reflections from the
inside of the lens barrel or cells or from the inside of the
shutter. I would say your experience with the Artar is
unusual.
The Apo Artar was designed for use on process cameras.
These were used for making printing plates, or rather,
negatives used to expose the photo-resists that were used to
control the etching of the plates. Process lenses are
designed to work best at magnifications near unity. The
Artar is designed for three-color work where the color
separation negatives must all be in focus and be of exactly
the same size. Although the lens is optimized for equal
object and image distance (unity magnification) it performs
very well even at infinity focus if stopped down a bit.
One cause of flare in lenses is haze but this won't
cause ghost images. Haze seems to form on many lenses with
time. I am not sure of the cause but the haze is easily
removed with any lens cleaner. The problem is getting to the
inside surfaces. Most Artars have back caps on the cells so
that cleaning the insides is not difficult.


--
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Richard Knoppow
Los Angeles, CA, USA

jjs wrote in message
...
"AAvK" wrote in message
...

What about for mono films? I think because of this
problem I
would never use this lens for color films!

I took it that Richard was addressing B&W. If aberation
occurs in a particular color for which the film is
sensitive, a correcting filter will help.

Black & White film is sensitive to color (obviously) and
not equally sensitive to all colors. Filters are
important.


Lack of color correction affects both B&W and color
although it manifests itself in different ways. Lenses have
two kinds of color aberration: one is longitudinal chromatic
aberration, the other is lateral chromatic aberration. The
first is the one we usually think of where the lens focuses
different colors at different distances: in effect the focal
length changes with color. This is inherent due to the
characteristics of glass and is reduced by balancing the
dispersion of the positive and negative elements by choosing
the kinds of glass used for them. The newer low-dispersion
glasses make the job of correcting color while maintaning
other corrections easier.
Lateral color is a difference in the _size_ of images at
different colors. The images are all in focus but different
in size so that there is still fringing. In fact, because
the images are all sharp the fringing may be more noticable.
Lateral color can be reduced by symmetry or by choice of
glass types. In non-symmetrical lenses it is sometimes
difficult to correct.
In a convertible lens, where the cells are similar but
can be used alone the correction for lateral color due to
symmetry is lost when only one cell is used. Some of these
lenses have cells which are corrected fairly well and others
show considerable color fringing when single cells are used
but all are inferior to the complete lens (two cells).
Color problems may actually be more appearant in B&W
because the film records everything at once and the eye can
not longer ignore some of the information at it can in color
pictures.
Now, if the colors recorded throught an aberrated lens
are limited the aberration will have less effect. Some very
old lenses are not very corrected for the red end of the
spectrum because before about the mid 1920's most film was
orthochromatic (not sensitive to red) or even "ordinary"
(not sensitize to any color but blue). A filter which
reduces red light may make such lenses sharper. Green
filters cut off some blue light and some red light so are
good choices where a lens has serious chromatic aberration.
A cyan filter will somewhat duplicate orthochromatic film
and will usually also improve sharpness when the lens has
some chromatic aberration.
My experience with the T-R lens is that the individual
cells have very noticable color fringing. The Zeiss
Convertible Protar is better although still having some
fringing. Even the older convertible version of the
Schneider Symmar has some fringing, actually a little worse
than the Protar.
A general purpose lens which was very well corrected for
both kinds of color aberration is the Kodak Commercial
Ektar. These are Tessar types and don't have the advantage
of symmetry but were very carefully designed to eliminate
color problems because they were intended to promote the use
of color film for commercial photography. Most symmetrical
or nearly symmetrical lenses have good correction for
lateral color, the Goerz Dagor, Dogmar and of course Artar
being examples.


--
---
Richard Knoppow
Los Angeles, CA, USA

[uppersnip]
---
Richard Knoppow
Los Angeles, CA, USA




Richard! So sorry for being so late, but it dawned on me to thank you very much for
your great and terrific help and for the sharing of knowledge, awesome kindness.

Thank you, very very much.


Regards,

--
Giant_Alex })))*
not my site: http://www.e-sword.net/