Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5

I seem to have two of these Xenars and an Ektar - came 'with' other things -
and was thinking I'd just sell them. I have a Rodenstock Sironar-N 100mm
f5.6 that has more modern coating (the Xenars are single coated) and wider
coverage, and is in a more accurate shutter (the others all need cleaning
and adjusting) so that's my main 'normal' lens for use on 6x9 roll-film
backs (it covers 6x12 nicely too.)

I know the Ektar has a good reputation, but I've never been all that
impressed by it. The Xenars I've never really used. So I was just thinking
I'd put all three up for sale, and then started to wonder. So, apart from
the speed of the Xenars, does anyone think there's any special quality to
any of these lenses that means I should keep one? Is the Xenar particularly
good for some type of work? If someone thinks yes, then I'll test both the
Xenars, and put the better shutter on the better lens and get it sorted
out - but otherwise I don't really feel I want to spend time testing lenses
that I don't _expect_ to keep...

ie., is it worth while even experimenting with these, or should I just sell
them and spend my time on something more profitable..?

Thanks for any opinions!


Peter
--
http://www.bard-hill.co.uk

From my limited experiience
(Used a 150/4.5 Schneider Xenar on 4x5)
They need stopped down to keep the corners sharp.
Otherwise, if one crops regularly, they're fine.

Never used an Ektar.

The Rodenstock would certainly be the one to keep of the three.
imnsho,

Collin
KC8TKA

In article . net,
Richard Knoppow wrote:

Bothe the Ektar and Xenar are Tessary type lenses. Any
Tessar type will be somewhat soft in the margins until
stopped down about 2 stops from maximum aperture. Both the
Xenar and Ektar are well designed lenses. Its hard to
compare them since the Xenar went through some design
changes over the years. I think perhaps the Ektar did also
but have no specific information.

In my experience, prewar Schneider lenses are pretty awful. I
don't know if poor design or poor quality control is to blame
for the low quality of the Xenars I've used in the past but I
would prefer the Ektar to them any day.

Later Schneider lenses, of course, are much, much better.

--
Thor Lancelot Simon

"We cannot usually in social life pursue a single value or a single moral
aim, untroubled by the need to compromise with others." - H.L.A. Hart

"Thor Lancelot Simon" wrote in message
...
In article
. net,
Richard Knoppow wrote:

Bothe the Ektar and Xenar are Tessary type lenses. Any
Tessar type will be somewhat soft in the margins until
stopped down about 2 stops from maximum aperture. Both the
Xenar and Ektar are well designed lenses. Its hard to
compare them since the Xenar went through some design
changes over the years. I think perhaps the Ektar did also
but have no specific information.

In my experience, prewar Schneider lenses are pretty
awful. I
don't know if poor design or poor quality control is to
blame
for the low quality of the Xenars I've used in the past
but I
would prefer the Ektar to them any day.

Later Schneider lenses, of course, are much, much better.

--
Thor Lancelot Simon


I haven't dealt with enough pre-WW-2 (have to make it
clear to the younger folks just which war) Schneider lenses
to be sure but my impression is that Schneider was something
of an economy brand with less than wonderful QC, but then
most lens QC was not very good at the time. Kodak, after
Rudolf Kingslake took over the optical department (about
1939) was making surpurb lenses with very good QC. Kodak
developed the rare earth glasses discovered at the National
Bureau of Standards into a commercial product and began
using them at about this time. None were used in the Ektar
series made for small sheet film cameras although I think
the first Kodak lens to employ the new glass was the Heliar
type series designed by Fred Altman. The lens in the
Medalist camera, the 50mm and 75mm Enlarging Ektars, and the
105mm, f/3.7 lens for small Speed Graphics is of this type.
I have a prototype Schneider Angulon, made in 1929 before
the patent was issued. It has severe color fringing due to a
design error. If one sets up the lens shown in the patent in
a computer lens design program the chromatic error is
apparent. Evidently the lens was later re-designed because
later versions of the Angulon do not have this problem.
Judging from various lenses I have and from the general
reputation it appears that Kodak, Zeiss, and Goerz-American
had pretty good QC comparitively but one still had to check
out individual lenses to avoid dogs.
Post war Schneider seems to have completely turned around
making some excellent lenses with good QC.
Another manufacturer with a somewhat uncertain reputation
is Wollensak. When I started out in the 1950's Wollensak was
considered junk. Some of their lenses were indeed pretty
awful but they also made some very good ones and excellent
shutters, so you never know.


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

Richard Knoppow wrote:
. . . . . . . .
Also, even though its not intended to be a convertible
the rear element can be used alone as a long focus lens at
about f/12.5 maximum aperture. It will not be as sharp as
the combined lens but may be useful for portrait or other
purposes where one wants a longer lens and reduced sharpness
is acceptable or even desirable.




Seems to be somewhat true of a few six element four group modern lenses.
I tried a couple as you imply with just removing the rear groups. It
seems like roughly double the focal length, at least just judging it by
focusing on the ground glass, and measuring the bed extension . . . does
that seem about right, or some sort of rule of thumb for doing this?

Seems like maybe lots of lenses could be used as a convertible lens.
Again, just judging on the ground glass, it was softer wide open, which
made focus a little tougher. Stopping down helped focus. Any comments
appreciated.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com

"Bandicoot" wrote in message
...

Thanks everyone for these thoughts - sounds like I'll continue with the
Sironar-N as my preferred choice as at present, and let the Ektar and Xenars
go without spending more time (and time is money!) on them. Much as I
thought, but a second opinion or two is always very comforting :-)

Interesting idea about using the Plasmat type lenses as pseudo
convertibles - makes sense but I'd just never thought about it before. That
might be fun to play with some time - and I do have a job scheduled for the
summer that needs a somewhat soft lens...

Thanks everyone,



Peter

"Gordon Moat" wrote in message
...


Richard Knoppow wrote:
. . . . . . . .
Also, even though its not intended to be a convertible
the rear element can be used alone as a long focus lens
at about f/12.5 maximum aperture. It will not be as sharp
as the combined lens but may be useful for portrait or
other purposes where one wants a longer lens and reduced
sharpness is acceptable or even desirable.




Seems to be somewhat true of a few six element four group
modern lenses. I tried a couple as you imply with just
removing the rear groups. It seems like roughly double the
focal length, at least just judging it by focusing on the
ground glass, and measuring the bed extension . . . does
that seem about right, or some sort of rule of thumb for
doing this?

Seems like maybe lots of lenses could be used as a
convertible lens. Again, just judging on the ground glass,
it was softer wide open, which made focus a little
tougher. Stopping down helped focus. Any comments
appreciated.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com


Any symmetrical lens can be used as a convertible. Those
which are designed for it may have some additional
corrections to the individual cells which are not needed
when used as a combined lens. The best known example is the
Zeiss Series VII Protar. The individual cells are corrected
for coma. Normally, in a symmetrical lens, the symmetry
automatically corrects the coma. Many older lenses
advertised as convertibles are not so corrected, the Dagor
is an example. A single Dagor cell can be used but must be
stopped down to around f/45 to be reasonably sharp in the
corners. A Protar cell will give pretty sharp images at
around f/32. In addition, the Protar allows the use of mixed
focal lengths in combination. As a combined lens the Protar
is no better than the Dagor but the individual cells are
significantly better.
Plasmat type lenses are derived from the Dagor but have
enough extra degrees of freedom to provide coma correction
to individual cells if desired. The original version of the
f/5.6 Schneider Symmar was like this. Schneider discovered
that there was really not much call for the convertible
feature and that the performance of the combined lens could
be improved by eliminating it. The front and rear cells can
still be used but must be stopped down more than the older
version.
Ideally, the single cell of a convtible should be used
behind the stop. However, the spacing between the lens and
the stop is seldom ideal for the single lens so performance
is not a whole lot better than when used in front. Since the
individual cells are slighly retrofocus when the convex side
faces the film and slightly telephoto when faced the other
way the bellows draw will be significantly less when the
lens is in front of the stop. This will often allow the use
of a longer FL lens on a given camera. When cells of
different focal lengths are used, as in the Convertible
Protar or Symmar, the longer FL goes on the front for best
correction. This can be reversed when using the lens for
very close objects.
The f/5.6 Symmar and Rodenstock Sironar are slightly
asymmetrical, that is, the two cells do not have the same
focal length. This is done to improve the correction for
distant objects. Perfectly symmetrical lenses are optimum
where the entire optical system is symmetrical, that is
equal image and object distances or a magnification of 1:1.
The loss of correction for common symmetrical lenses, like
the Dagor or Apochromatic Artar, is not great and is
normally compensated by stopping down .
My reference to the f/5.6 Symmar is to distinguish it
from a much earlier lens of that name, the f/6.8 Symmar,
which is a Dagor knock-off.


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

Richard Knoppow wrote:
"Gordon Moat" wrote in message
...


Richard Knoppow wrote:

. . . . . . . .
Also, even though its not intended to be a convertible
the rear element can be used alone as a long focus lens
at about f/12.5 maximum aperture. It will not be as sharp
as the combined lens but may be useful for portrait or
other purposes where one wants a longer lens and reduced
sharpness is acceptable or even desirable.




Seems to be somewhat true of a few six element four group
modern lenses. I tried a couple as you imply with just
removing the rear groups. It seems like roughly double the
focal length, at least just judging it by focusing on the
ground glass, and measuring the bed extension . . . does
that seem about right, or some sort of rule of thumb for
doing this?

Seems like maybe lots of lenses could be used as a
convertible lens. Again, just judging on the ground glass,
it was softer wide open, which made focus a little
tougher. Stopping down helped focus. Any comments
appreciated.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com


Any symmetrical lens can be used as a convertible. Those
which are designed for it may have some additional
corrections to the individual cells which are not needed
when used as a combined lens. The best known example is the
Zeiss Series VII Protar. The individual cells are corrected
for coma. Normally, in a symmetrical lens, the symmetry
automatically corrects the coma. Many older lenses
advertised as convertibles are not so corrected, the Dagor
is an example. A single Dagor cell can be used but must be
stopped down to around f/45 to be reasonably sharp in the
corners. A Protar cell will give pretty sharp images at
around f/32. In addition, the Protar allows the use of mixed
focal lengths in combination. As a combined lens the Protar
is no better than the Dagor but the individual cells are
significantly better.
Plasmat type lenses are derived from the Dagor but have
enough extra degrees of freedom to provide coma correction
to individual cells if desired. The original version of the
f/5.6 Schneider Symmar was like this. Schneider discovered
that there was really not much call for the convertible
feature and that the performance of the combined lens could
be improved by eliminating it. The front and rear cells can
still be used but must be stopped down more than the older
version.

So I am seeing a not quite symmetrical design behave like a telephoto
with the rear cells removed. Perhaps interesting that I am trying this
with Schneider lenses.




Ideally, the single cell of a convtible should be used
behind the stop. However, the spacing between the lens and
the stop is seldom ideal for the single lens so performance
is not a whole lot better than when used in front. Since the
individual cells are slighly retrofocus when the convex side
faces the film and slightly telephoto when faced the other
way the bellows draw will be significantly less when the
lens is in front of the stop. This will often allow the use
of a longer FL lens on a given camera. When cells of
different focal lengths are used, as in the Convertible
Protar or Symmar, the longer FL goes on the front for best
correction. This can be reversed when using the lens for
very close objects.

That gives me an idea to try the lens with rear cell removed, and
reversed in the holder. Makes getting at the lens aperture and shutter
controls tougher, but might be interesting.


The f/5.6 Symmar and Rodenstock Sironar are slightly
asymmetrical, that is, the two cells do not have the same
focal length. This is done to improve the correction for
distant objects. Perfectly symmetrical lenses are optimum
where the entire optical system is symmetrical, that is
equal image and object distances or a magnification of 1:1.
The loss of correction for common symmetrical lenses, like
the Dagor or Apochromatic Artar, is not great and is
normally compensated by stopping down .
My reference to the f/5.6 Symmar is to distinguish it
from a much earlier lens of that name, the f/6.8 Symmar,
which is a Dagor knock-off.



Okay, I did some searching, and found Symmar, Symmar-S, APO Symmar, and
Super Symmar. I read some claims that the Symmar-S and APO Symmar at
f5.6 are actually the same, with only a name change from Schneider. I do
note some differences in coverage in more recent lenses with the same
names, but not much else different.

Also on the naming of lens designs, wouldn't a perfectly symmetrical six
element four group lens be a Double Gauss? And isn't a Symmar or Sironar
just a slight variation on that? Thanks for all the great information.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com

"Gordon Moat" wrote in message
...


Richard Knoppow wrote:
"Gordon Moat" wrote in message
...


Richard Knoppow wrote:

So I am seeing a not quite symmetrical design behave like
a telephoto with the rear cells removed. Perhaps
interesting that I am trying this with Schneider lenses.

Lots of snipping here....



Ideally, the single cell of a convtible should be used
behind the stop. However, the spacing between the lens
and the stop is seldom ideal for the single lens so
performance is not a whole lot better than when used in
front. Since the individual cells are slighly retrofocus
when the convex side faces the film and slightly
telephoto when faced the other way the bellows draw will
be significantly less when the lens is in front of the
stop. This will often allow the use of a longer FL lens
on a given camera. When cells of different focal lengths
are used, as in the Convertible Protar or Symmar, the
longer FL goes on the front for best correction. This can
be reversed when using the lens for very close objects.

That gives me an idea to try the lens with rear cell
removed, and reversed in the holder. Makes getting at the
lens aperture and shutter controls tougher, but might be
interesting.

The difference will be slight and not worth the trouble
it would take to use it that way.


The f/5.6 Symmar and Rodenstock Sironar are slightly
asymmetrical, that is, the two cells do not have the same
focal length. This is done to improve the correction for
distant objects. Perfectly symmetrical lenses are optimum
where the entire optical system is symmetrical, that is
equal image and object distances or a magnification of
1:1. The loss of correction for common symmetrical
lenses, like the Dagor or Apochromatic Artar, is not
great and is normally compensated by stopping down .
My reference to the f/5.6 Symmar is to distinguish it
from a much earlier lens of that name, the f/6.8 Symmar,
which is a Dagor knock-off.



Okay, I did some searching, and found Symmar, Symmar-S,
APO Symmar, and Super Symmar. I read some claims that the
Symmar-S and APO Symmar at f5.6 are actually the same,
with only a name change from Schneider. I do note some
differences in coverage in more recent lenses with the
same names, but not much else different.


Schneider began using the name Symmar in the 1930's if
not even earlier for their version of the Dagor. The Dagor
patent would have expired in about 1922 in Germany (where
the patent life was 20 years instead of 17 as in the USA).
Later, they used the same name for a Plasmat lens, beginning
in the 1950's (I don't know the exact date.
The original Dagor type was an f/6.8 lens, the later
version f/5.6.

Also on the naming of lens designs, wouldn't a perfectly
symmetrical six element four group lens be a Double Gauss?
And isn't a Symmar or Sironar just a slight variation on
that? Thanks for all the great information.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com


The Plasmat was derived from the Dagor replacing one of
the cemented interfaces with an air space. This gives the
designer the additional degrees of freedom, a curvature and
a spacing, to get better control of the residual spherical
aberration typical of the Dagor type. In addition, the
Plasmat can be exceptionally well corrected for astigmatism.
Coma, lateral color, and geometrical distortion are
automatically corrected by symmetry. However, this
correction is best at an equal film and subject distance
when the lens is perfectly symmetrical. Correction for
distant objects can be improved in a symmetrical lens of any
type by shifting some power from one group to the other.
This is done in Plasmat lenses like the current Symmar, the
Rodenstock Sironar, and many others of this type. Since the
individual cells of these lenses will form images they can
be used alone with some reduction in performance. The focal
lengths will depend on the individual lens design. The Dagor
cells have a focal length of about 1.8X the combined lens
and are about f/13 when used behind the stop and about f/12
when used in front of it, the difference being due to the
magfication of the stop (entrance pupil) by the lens.
Double Gauss lenes are of a different form. The original
Gauss lens was designed as a telescope objective. It
consisted of two air-spaced meniscus elements, a positive
one and a negative one. The advantage of the Gauss lens is
that it can be very well color corrected. By mounting two
such objectives back to back around a stop, the advantages
of symmetry can be gained. The Double Gauss type is very
versitile, it is the type used for many medium wide angle
lenses like the Kodak Wide Field Ektar and, with the
addition of compounded inner components, as the
Planar/Opic/Biotar type used for most lenses of f/2 or
faster for 35mm cameras and many f/2.5 lenses for medium
format cameras. In contrast with the Plasmat, the Planar
type has better correction for spherical but narrower
coverage. The original Planar, designed by Paul Rudolph, the
inventor of the Tessar, was a fully symmetrical lens. The
first to modify it by making it slightly asymmetrical was
Horace Lee, of Taylor, Taylor, and Hobson, as the Opic. The
lens became more popular as the Zeiss Biotar designed by
Willie Merte. It is probably the most used complex lens
design.
There are other symmetrical designs and other meniscus
lenses which are not related to the Gauss lens. For
instance, the "Dialyte" type, a four element air-spaced lens
examples of which include the Goerz Celor, Dogmar, and
Apochromatic Artar. The difference is that in a Double Gauss
lens all the surfaces are concave toward the stop. In a
Dialyte, the elements are are either bi-convex, bi-concave,
or have one plane surface. The Double Gauss can be made
quite wide angle, the Dialyte is inherently rather narrow in
coverage. The Dialyte has the virtue of having corrections
which do not change much with the object distance. It was
very widely used for process work where excellent
corrections were necessary but wide angle coverage was not.
So, to directly answer you question above, a six element
in four groups _could_ be a double Gauss lens, as in a
Biotar or any of a zillion lenses made for 35mm cameras, or,
it could be a Plasmat, depending on which elements are
cemented. In the Double Gauss, the cemented elements are the
negative elements closest to the stop, in a Plasmat they are
the outer group plus the inner element is positive rather
than negative.
This is probably more than you ever wanted to know.


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

Richard Knoppow wrote:


"Gordon Moat" wrote in message
...

. . . . . . . . . . .
That gives me an idea to try the lens with rear cell
removed, and reversed in the holder. Makes getting at the
lens aperture and shutter controls tougher, but might be
interesting.


The difference will be slight and not worth the trouble
it would take to use it that way.


I ended up just trying it on the ground glass, and I agree that the very
slight difference is not worth using.

. . . . . . . . . . . . . . . .

Okay, I did some searching, and found Symmar, Symmar-S,
APO Symmar, and Super Symmar. I read some claims that the
Symmar-S and APO Symmar at f5.6 are actually the same,
with only a name change from Schneider. I do note some
differences in coverage in more recent lenses with the
same names, but not much else different.



Schneider began using the name Symmar in the 1930's if
not even earlier for their version of the Dagor. The Dagor
patent would have expired in about 1922 in Germany (where
the patent life was 20 years instead of 17 as in the USA).
Later, they used the same name for a Plasmat lens, beginning
in the 1950's (I don't know the exact date.
The original Dagor type was an f/6.8 lens, the later
version f/5.6.


So this makes it a very long running design for Schneider. The original
idea must have been quite good to just lead to later evolutionary
variations. I would guess the Super Symmar is still somewhat like the
original idea, just looking at the cross section of the optics on the
Schneider data sheet.


Also on the naming of lens designs, wouldn't a perfectly
symmetrical six element four group lens be a Double Gauss?
And isn't a Symmar or Sironar just a slight variation on
that? Thanks for all the great information.



The Plasmat was derived from the Dagor replacing one of
the cemented interfaces with an air space. This gives the
designer the additional degrees of freedom, a curvature and
a spacing, to get better control of the residual spherical
aberration typical of the Dagor type. In addition, the
Plasmat can be exceptionally well corrected for astigmatism.
Coma, lateral color, and geometrical distortion are
automatically corrected by symmetry. However, this
correction is best at an equal film and subject distance
when the lens is perfectly symmetrical. Correction for
distant objects can be improved in a symmetrical lens of any
type by shifting some power from one group to the other.
This is done in Plasmat lenses like the current Symmar, the
Rodenstock Sironar, and many others of this type. Since the
individual cells of these lenses will form images they can
be used alone with some reduction in performance. The focal
lengths will depend on the individual lens design. The Dagor
cells have a focal length of about 1.8X the combined lens
and are about f/13 when used behind the stop and about f/12
when used in front of it, the difference being due to the
magfication of the stop (entrance pupil) by the lens

So this is what I was seeing on the ground glass as the difference in
focal length. Seemed like it was closer to 2x, though my measuring was
informal and 1.8x seems about correct for what was on the ground glass.
I think I could find a use for this if I ever did portraits.


..
Double Gauss lenes are of a different form. The original
Gauss lens was designed as a telescope objective. It
consisted of two air-spaced meniscus elements, a positive
one and a negative one. The advantage of the Gauss lens is
that it can be very well color corrected. By mounting two
such objectives back to back around a stop, the advantages
of symmetry can be gained. The Double Gauss type is very
versitile, it is the type used for many medium wide angle
lenses like the Kodak Wide Field Ektar and, with the
addition of compounded inner components, as the
Planar/Opic/Biotar type used for most lenses of f/2 or
faster for 35mm cameras and many f/2.5 lenses for medium
format cameras. In contrast with the Plasmat, the Planar
type has better correction for spherical but narrower
coverage. The original Planar, designed by Paul Rudolph, the
inventor of the Tessar, was a fully symmetrical lens. The
first to modify it by making it slightly asymmetrical was
Horace Lee, of Taylor, Taylor, and Hobson, as the Opic. The
lens became more popular as the Zeiss Biotar designed by
Willie Merte. It is probably the most used complex lens
design.

I have used a few 35 mm lenses that would fit into this family of designs.

. . . . . . . . . . . . . .
So, to directly answer your question above, a six element
in four groups _could_ be a double Gauss lens, as in a
Biotar or any of a zillion lenses made for 35mm cameras, or,
it could be a Plasmat, depending on which elements are
cemented. In the Double Gauss, the cemented elements are the
negative elements closest to the stop, in a Plasmat they are
the outer group plus the inner element is positive rather
than negative.
This is probably more than you ever wanted to know.



Actually, I enjoyed this discussion. It is a little of the history of
lenses, history of photography, and makes a great deal of sense for why
we have the modern designs we now often use in large format imaging. All
these considerations made by the earlier designers have led to some
quite good optics. Thanks for the discussion.

Ciao!

Gordon Moat
A G Studio
http://www.allgstudio.com