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#1
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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 |
#2
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
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 |
#3
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
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 |
#4
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
"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 |
#5
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
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 |
#6
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
"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 |
#7
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
"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 |
#8
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
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 |
#9
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
"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 |
#10
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Schneider Xenar 105mm f3.5, Kodak Ektar 101mm f4.5
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 |
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