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#11
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Enlarger lens options.
"Nicholas O. Lindan" wrote in message
m... The law of diminishing returns. When something is close to perfection the cost of even a miniscule gain becomes astronomical. Sometimes astronauts become miniscule. It evens out. spend the savings on something worthwhile that will make a noticeable and unequivocal improvement: a trip to someplace photogenic, a workshop, a really good timer ... I got a good timer but I'm not having a good time. |
#12
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Enlarger lens options.
Richard Knoppow wrote:
A high power grain focuser will often show up differences in lenses that are much harder to see in a print but may also introduce its own problems, for instance, some grain focusers are not very well achromitized and will show color fringes due to its own optics which are not present in the image from the enlarging lens. I made a comparison between some better enlarging lenses for 24x36mm (Apo-Rodagon 2.8/50, Componon-S 2.8/50, Focotar 4.5/50, Focotar 2.8/40 and Rodagon 4/60) and compared them at about 8x enlargement (20x30cm paper size). Each was perfectly adjusted using a Peak #1, a glass carrier and all enlarger planes were adjusted parallel using a laser tool. All lenses were closed 2 stops from wide open. The result: The only one you could distinguish from the others was the old Focotar 4.5/50. It had a little curvature of field visible at the extreme edges. That's all... no visible difference for the other lenses. You can see the differences between the lenses with the Peak #1. The curvature of field is readily visible for the two Focotars. The two Rodagon and the Componon-S were much better and nearly identical. The Apo-Rodagon was a little better wide open than the others, but all 2.8 lenses were unuseable with this opening (for my view of quality...). Stopped down, all were excellent. Martin |
#13
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Enlarger lens options.
"Martin J" wrote in message ... Richard Knoppow wrote: A high power grain focuser will often show up differences in lenses that are much harder to see in a but may also introduce its own problems, for instance, some grain focusers are not very well achromitized and will show color fringes due to its own optics which are not present in the image from the enlarging lens. I made a comparison between some better enlarging lenses for 24x36mm (Apo-Rodagon 2.8/50, Componon-S 2.8/50, Focotar 4.5/50, Focotar 2.8/40 and Rodagon 4/60) and compared them at about 8x enlargement (20x30cm paper size). Each was perfectly adjusted using a Peak #1, a glass carrier and all enlarger planes were adjusted parallel using a laser tool. All lenses were closed 2 stops from wide open. The result: The only one you could distinguish from the others was the old Focotar 4.5/50. It had a little curvature of field visible at the extreme edges. That's all... no visible difference for the other lenses. You can see the differences between the lenses with the Peak #1. The curvature of field is readily visible for the two Focotars. The two Rodagon and the Componon-S were much better and nearly identical. The Apo-Rodagon was a little better wide open than the others, but all 2.8 lenses were unuseable with this opening (for my view of quality...). Stopped down, all were excellent. Martin That's quite interesting. I suspect the Rodagon and Componon designs are quite similar although I don't have the actual prescriptions. Since its likely all the relatively modern lenses were designed with the aid of computers I suspect the performance should be much alike. I think the Focotar is an older design. One of the characteristics of the generic Plasmat type, which is what the Rodagon and Componon are, is that they can be unusually well corrected for astigmatism. Forgoing an explanation of what exactly that is (different in a camera lens than in opthalmic lenses) it leads to being able to get a very flat field. While both manufacturers claim superiority I suspect its pretty much a draw. Some think the Rodagon is mechanically superior to the Componon. Do your lenses have metal or plastic iris blades? -- --- Richard Knoppow Los Angeles, CA, USA |
#14
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Enlarger lens options.
Richard Knoppow wrote:
That's quite interesting. I suspect the Rodagon and Componon designs are quite similar although I don't have the actual prescriptions. Since its likely all the relatively modern lenses were designed with the aid of computers I suspect the performance should be much alike. I think the Focotar is an older design. One of the characteristics of the generic Plasmat type, which is what the Rodagon and Componon are, is that they can be unusually well corrected for astigmatism. Forgoing an explanation of what exactly that is (different in a camera lens than in opthalmic lenses) it leads to being able to get a very flat field. While both manufacturers claim superiority I suspect its pretty much a draw. Some think the Rodagon is mechanically superior to the Componon. Do your lenses have metal or plastic iris blades? When I first got into 4x5" work, in the mid 1970s, I got a Schneider Componon-S f/5.6 to f/45 180mm enlarging lens, # 11 973 xxx. It works fine. Its diaphragm has lots of blades (about 19 of them), enough to make the aperture look round, and they appear to be metal. At least 10 years later, I got a Componon-S f/5.6 to f/45 150mm lens, # 14 588 yyy. It has only 5 blades, so the aperture looks approximately like a pentagon (except the edges are not quite straght. I cannot tell if they are metal or plastic; the 180 blades are shinier than the 150 and darker, reminding me of blackened brass (but I do not know what they are for sure), and the 150 blades are duller, but slightly lighter in color and rougher, reminding me of anodized aluminum (but I very much doubt they would actually be aluminum). Perhaps that is what plastic blades look like. For normal photograph use, is there any benefit to having a round aperture? I know in half-tone work with a sealed half-tone screen, there is a benefit to having a square aperture, but round holes work OK -- you just get a little bit of a different transfer function from the original to the half-tone. Unless you use the lens in the hot sun or something, there might even be a slight benefit to having plastic iris blades: less likely to rust or corrode. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 06:35:01 up 2 days, 23:07, 3 users, load average: 4.19, 4.16, 4.08 |
#15
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Enlarger lens options.
"Jean-David Beyer" wrote in message news:rbfVj.1212$OT1.79@trnddc03... Richard Knoppow wrote: That's quite interesting. I suspect the Rodagon and Componon designs are quite similar although I don't have the actual prescriptions. Since its likely all the relatively modern lenses were designed with the aid of computers I suspect the performance should be much alike. I think the Focotar is an older design. One of the characteristics of the generic Plasmat type, which is what the Rodagon and Componon are, is that they can be unusually well corrected for astigmatism. Forgoing an explanation of what exactly that is (different in a camera lens than in opthalmic lenses) it leads to being able to get a very flat field. While both manufacturers claim superiority I suspect its pretty much a draw. Some think the Rodagon is mechanically superior to the Componon. Do your lenses have metal or plastic iris blades? When I first got into 4x5" work, in the mid 1970s, I got a Schneider Componon-S f/5.6 to f/45 180mm enlarging lens, # 11 973 xxx. It works fine. Its diaphragm has lots of blades (about 19 of them), enough to make the aperture look round, and they appear to be metal. At least 10 years later, I got a Componon-S f/5.6 to f/45 150mm lens, # 14 588 yyy. It has only 5 blades, so the aperture looks approximately like a pentagon (except the edges are not quite straght. I cannot tell if they are metal or plastic; the 180 blades are shinier than the 150 and darker, reminding me of blackened brass (but I do not know what they are for sure), and the 150 blades are duller, but slightly lighter in color and rougher, reminding me of anodized aluminum (but I very much doubt they would actually be aluminum). Perhaps that is what plastic blades look like. For normal photograph use, is there any benefit to having a round aperture? I know in half-tone work with a sealed half-tone screen, there is a benefit to having a square aperture, but round holes work OK -- you just get a little bit of a different transfer function from the original to the half-tone. Unless you use the lens in the hot sun or something, there might even be a slight benefit to having plastic iris blades: less likely to rust or corrode. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 06:35:01 up 2 days, 23:07, 3 users, load average: 4.19, 4.16, 4.08 |
#16
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Enlarger lens options.
"Jean-David Beyer" wrote in message news:rbfVj.1212$OT1.79@trnddc03... Richard Knoppow wrote: That's quite interesting. I suspect the Rodagon and Componon designs are quite similar although I don't have the actual prescriptions. Since its likely all the relatively modern lenses were designed with the aid of computers I suspect the performance should be much alike. I think the Focotar is an older design. One of the characteristics of the generic Plasmat type, which is what the Rodagon and Componon are, is that they can be unusually well corrected for astigmatism. Forgoing an explanation of what exactly that is (different in a camera lens than in opthalmic lenses) it leads to being able to get a very flat field. While both manufacturers claim superiority I suspect its pretty much a draw. Some think the Rodagon is mechanically superior to the Componon. Do your lenses have metal or plastic iris blades? When I first got into 4x5" work, in the mid 1970s, I got a Schneider Componon-S f/5.6 to f/45 180mm enlarging lens, # 11 973 xxx. It works fine. Its diaphragm has lots of blades (about 19 of them), enough to make the aperture look round, and they appear to be metal. At least 10 years later, I got a Componon-S f/5.6 to f/45 150mm lens, # 14 588 yyy. It has only 5 blades, so the aperture looks approximately like a pentagon (except the edges are not quite straght. I cannot tell if they are metal or plastic; the 180 blades are shinier than the 150 and darker, reminding me of blackened brass (but I do not know what they are for sure), and the 150 blades are duller, but slightly lighter in color and rougher, reminding me of anodized aluminum (but I very much doubt they would actually be aluminum). Perhaps that is what plastic blades look like. For normal photograph use, is there any benefit to having a round aperture? I know in half-tone work with a sealed half-tone screen, there is a benefit to having a square aperture, but round holes work OK -- you just get a little bit of a different transfer function from the original to the half-tone. Unless you use the lens in the hot sun or something, there might even be a slight benefit to having plastic iris blades: less likely to rust or corrode. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 06:35:01 up 2 days, 23:07, 3 users, load average: 4.19, 4.16, 4.08 It appears that the shape of the iris affects out of focus areas of the image. This is perhaps part of the effect called bokeh by the Japanese. In any case bright points which are not sharply focused are rendered in the shape of the iris. This may not be as noticable for enlarging where a flat surface is imaged onto another flat surface. In making half-tone plates the iris is imaged by the half tone screen as an array of spots or dots. By using a square aperture the intestices of the dots are at the corners so the variation is smoother. For color work each of the images is photographed using an iris with a lozenge-shaped aperture at a different angle. I can't remember now if this is to prevent moir but I think it is. In any case there is an optimum set of angles for the apertures. These apertures are usually in the form of Waterhouse stops and is the reason process lenses usually have a slot in the side. My barrel mounted Apo-Artars have the slot but the shutter mounted one does not. The barrel mounted Artars also have 20 blade irises and a very nearly perfectly round hole. -- --- Richard Knoppow Los Angeles, CA, USA |
#17
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Enlarger lens options.
Richard Knoppow wrote:
It appears that the shape of the iris affects out of focus areas of the image. This is perhaps part of the effect called bokeh by the Japanese. In any case bright points which are not sharply focused are rendered in the shape of the iris. This may not be as noticable for enlarging where a flat surface is imaged onto another flat surface. In making half-tone plates the iris is imaged by the half tone screen as an array of spots or dots. By using a square aperture the intestices of the dots are at the corners so the variation is smoother. Right, although I find that a round hole is not too bad. But I do halftone starting with a continuous tone negative (a positive print or other positive flat art is usually used) and make the half-tone on OrthoLith. These dots have soft edges (undesirable) so I contact print them onto another piece of OrthoLith to get a suitable half-tone negative. For color work each of the images is photographed using an iris with a lozenge-shaped aperture at a different angle. That might be so, but I never heard that. I can't remember now if this is to prevent moir[e] but I think it is. When my great grandfather (F. E. Ives) devised the process, he angled the half-tone screen to prevent moire, but AFAIK did not use lozenge shaped diaphragms. In any case there is an optimum set of angles for the apertures. This is true for the angles of the half-tone screens as well. In fact an amusing thing happened to F.E.Ives. When he first made color half-tones, he naturally angled the screens between the different colors. He did not bother to patent that because it was obvious. Years later someone else patented the idea of angling the screens and sued Ives. Ives had to go to court at considerable expense to prove that the patent was invalid both because it was obvious (kiss of death for patents) and because of over a decade of prior use. These apertures are usually in the form of Waterhouse stops and is the reason process lenses usually have a slot in the side. In any case a slot is needed to set the aperture (square or not) to the correct angle. This is all about sealed glass half-tone screens, not the plastic contact screens more recently used. Of course, with a round aperture, none of this makes any difference. My barrel mounted Apo-Artars have the slot but the shutter mounted one does not. The barrel mounted Artars also have 20 blade irises and a very nearly perfectly round hole. The 150 mm Componon-S 5-blade iris does not make a geometric pentagon. What would be straight edges are actually semi-circular convex to the edge of the lens. I.e., at the "corners" of the iris the diameter is larger than in the middle of what would be a straight line. In other words, the corners are farther from the center than would be expected if a true pentagon were used. This clearly because the iris blades are made that way. It would be perfectly easy to make them straight if Schneider had wanted to. I assume this was done for optical reasons and not to make the mechanics cheaper. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 11:35:01 up 3 days, 4:07, 3 users, load average: 4.16, 4.13, 4.08 |
#18
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Enlarger lens options.
"Jean-David Beyer" wrote in message news:uujVj.930$%X1.495@trnddc08... Richard Knoppow wrote: It appears that the shape of the iris affects out of focus areas of the image. This is perhaps part of the effect called bokeh by the Japanese. In any case bright points which are not sharply focused are rendered in the shape of the iris. This may not be as noticable for enlarging where a flat surface is imaged onto another flat surface. In making half-tone plates the iris is imaged by the half tone screen as an array of spots or dots. By using a square aperture the intestices of the dots are at the corners so the variation is smoother. Right, although I find that a round hole is not too bad. But I do halftone starting with a continuous tone negative (a positive print or other positive flat art is usually used) and make the half-tone on OrthoLith. These dots have soft edges (undesirable) so I contact print them onto another piece of OrthoLith to get a suitable half-tone negative. For color work each of the images is photographed using an iris with a lozenge-shaped aperture at a different angle. That might be so, but I never heard that. I can't remember now if this is to prevent moir[e] but I think it is. When my great grandfather (F. E. Ives) devised the process, he angled the half-tone screen to prevent moire, but AFAIK did not use lozenge shaped diaphragms. In any case there is an optimum set of angles for the apertures. This is true for the angles of the half-tone screens as well. In fact an amusing thing happened to F.E.Ives. When he first made color half-tones, he naturally angled the screens between the different colors. He did not bother to patent that because it was obvious. Years later someone else patented the idea of angling the screens and sued Ives. Ives had to go to court at considerable expense to prove that the patent was invalid both because it was obvious (kiss of death for patents) and because of over a decade of prior use. These apertures are usually in the form of Waterhouse stops and is the reason process lenses usually have a slot in the side. In any case a slot is needed to set the aperture (square or not) to the correct angle. This is all about sealed glass half-tone screens, not the plastic contact screens more recently used. Of course, with a round aperture, none of this makes any difference. My barrel mounted Apo-Artars have the slot but the shutter mounted one does not. The barrel mounted Artars also have 20 blade irises and a very nearly perfectly round hole. The 150 mm Componon-S 5-blade iris does not make a geometric pentagon. What would be straight edges are actually semi-circular convex to the edge of the lens. I.e., at the "corners" of the iris the diameter is larger than in the middle of what would be a straight line. In other words, the corners are farther from the center than would be expected if a true pentagon were used. This clearly because the iris blades are made that way. It would be perfectly easy to make them straight if Schneider had wanted to. I assume this was done for optical reasons and not to make the mechanics cheaper. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 11:35:01 up 3 days, 4:07, 3 users, load average: 4.16, 4.13, 4.08 I think you may be right that its the screens which are made at an angle rather than the aperture, its been too long since I learned about this stuff and the books are not handy. Soft dot edges have always been a problem. Monckhoven's intensifier was intended to remedy this. It has the peculiar property of being both an intensifier and reducer because the cyanide will dissolve the low density silver before the intensifier works so the net result is to increase the contrast of the edges of the dots. -- --- Richard Knoppow Los Angeles, CA, USA |
#19
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Enlarger lens options.
Richard Knoppow wrote:
I think you may be right that its the screens which are made at an angle rather than the aperture, its been too long since I learned about this stuff and the books are not handy. Soft dot edges have always been a problem. Monckhoven's intensifier was intended to remedy this. It has the peculiar property of being both an intensifier and reducer because the cyanide will dissolve the low density silver before the intensifier works so the net result is to increase the contrast of the edges of the dots. I know F.E.Ives used special treatment of the negatives, and careful control of their condition for best results. They did not have litho film in those days. They do now (for a while more, at least), so I make contact prints of the soft-dot stuff onto another piece of litho film and that makes hard-dots. Exposure is tricky at first, because if you change the exposure, you change the diameter of the dots. I make some 50% dots (my densitometer will measure % dot area) and make the contact prints 50% also -- or pretty close anyway. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 18:40:01 up 4 days, 11:12, 4 users, load average: 4.31, 4.37, 4.31 |
#20
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Enlarger lens options.
On 5/10/2008 8:02 AM Richard Knoppow spake thus:
In making half-tone plates the iris is imaged by the half tone screen as an array of spots or dots. By using a square aperture the intestices of the dots are at the corners so the variation is smoother. For color work each of the images is photographed using an iris with a lozenge-shaped aperture at a different angle. I can't remember now if this is to prevent moir but I think it is. Yes, the screens are angled to prevent moiré. By the way, the standard screen angles for 4-color (CMYK) printing a K (black): 45° M (magenta): 75° Y (yellow): 90° C (cyan): 105° So far as I know, these have been in use as long as 4-color halftone printing has been around. -- The best argument against democracy is a five-minute conversation with the average voter. - Attributed to Winston Churchill |
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