Apo-Rodagons are so good that many (Rodenstock too) make adapter for 35 mm cameras so they can fit on it for macro photography. It is hard to match 'em in that field too.
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Ed,apparently you're havng a problem understanding the concept, please allow me to clarify:
I take an out of focus picture of a tree, I make a print of it, I can still see that it is quite obviously a tree, however it is not sharp. Well maybe at f 32 with an enlarging lens you can still see grain, but that does not mean that the grain has been sharply defined or that the lens is sharp. And as I stated before unless you are using perspective controls during enlarging, there is no reason to go to f 22 or 32 as there are other means available for reducing brightness without causing loss of image quality.
Should someone lock their apertures, of course not but most professional photographers that I know, know what are the best apertures with their lenses and use those apertures whenever possible. And as I test every single camera lens I own at all the prime apertures I can state as fact that there are visible differences in even the finest optics at various apertures if one subjects the image to moderate to high magnification. Will most people see a difference under the most common uses, probably not. But I learned a long time ago that people have very wide ranging scales of what is acceptable and unacceptable quality. And maybe you and I are just on different scales.
Yes, I AM having trouble understanding your concept. I didn't say anything else. I said that I would THINK about that.
I would suggest that, possibly, *some here* do not see the relationship between resolution, acutance and apparent grain. Are you actually suggesting that defocusing, using "softeners", exceeding diffraction limits ... will ONLY have an effect on acutance/ sharpness - while having NO effect on "grain" appearance? - in any circumstance?
If so, that would be a revelation to me - I've tested many lenses "in my time" and I've never seen that happen yet.
I am not here to teach a "basic" course in optical design or theory. I said I would give the ideas here *DUE* consideration - and I have. Therefore, I'll continue on my way, using whatever enlarging lens aperture I deem appropriate, selecting that aperture from whatever choice is available.
Ed I agree that you're not here to teach a basic course in optical design theory, someone qualified to teach that would understand diffraction and would not be using f22-32 for their "exhibition prints". My point, and others here have made the same point is that grain can still be visible in an enlargement that suffers from diffraction and poor sharpness. It may appear mushy, or ill defined, but it will still appear. Anyway best of luck with your photography.
Surely there are two questions here.
One is Ed's contention (which I fully support) that the picture is the thing. Slavish devotion to ultimate technical quality can be an appalling constraint on creativity.
The other is twofold. First, it is difficult or impossible for a good picture to have too much quality, unless it is deliberately making use of what might in another picture be a 'fault'. Second, that quality will be compromised by some techniques, including too-small apertures for the enlarging lens.
The two are not wholly incompatible. So why are people on both sides getting so excited? The better the picture, the less technical quality matters; the only time you have too much technical quality is when someone says, "Gorgeous technique, shame about the subject matter and composition"
Cheers,
Roger
One is Ed's contention (which I fully support) that the picture is the thing. Slavish devotion to ultimate technical quality can be an appalling constraint on creativity.
The other is twofold. First, it is difficult or impossible for a good picture to have too much quality, unless it is deliberately making use of what might in another picture be a 'fault'. Second, that quality will be compromised by some techniques, including too-small apertures for the enlarging lens.
The two are not wholly incompatible. So why are people on both sides getting so excited? The better the picture, the less technical quality matters; the only time you have too much technical quality is when someone says, "Gorgeous technique, shame about the subject matter and composition"
Cheers,
Roger
Roger, do we all come to APUG, use film instead of the more available digital, many of us use large, expensive inconvenient camera formats, run film and developer tests, process our own film and print our own negatives because we don't care about quality?
The only way you get the ability to produce work of high technical quality is by taking the time and effort to pursue it. At the same time, to only pursue technical excellence at the expense of content is foolish.
Not a word of disagreement, and the heartiest possible endorsement of the last sentence.
Cheers,
Roger
I *must* work on my image.
Essentially, your argument is "I am right and you are wrong, because *I* understand - and you don't". And I firmly believe. with all honesty, that you expected me to buy that ... and what ... slink off into silence?
That did not happen - as usual , I *listen* and try to "see" the foundation for a view differing from mine. Try as I might, I could not see a correlation with my formal training in Geometrical Optics. Here, I had very little to evaluate, other than the classic "everybody knows". The "and others here agree with me", did not help much, either. I have absolutely no doubt that there were "others" who agreed with me as well. So...?
I will admit to some disappointment - I expected this discussion to continue on a higher level. You surprised me - I had the idea - and still believe - that you are far too intelligent than to attempt to use the "everyone knows" argument.
Diffraction, and it effects, was not a "gimme" subject. It took a great deal of study and work to pass that "module" ... and I made it. The worst module was "Polarization." I passed that one too, but I'm still a bit "rocky" about the concepts involved there. "Brewster" angle ...???
I'll tell you what ... I propose a single answer quiz, which, if answered correctly, will prove nothing, other than a familiarity with one minor aspect of Geometrical Optics:
In calculating the aperture that will be the limit where diffraction will not degrade the performance of a lens beyond its specific design criteria, the "circle of confusion" is an important factor. The values used are 1/60th mm for the 35mm format and 1/30th mm for "Medium" format.
How are the diameters of those "circles" determined?
Good luck to you too ... both with your photography and the above.
Ed I don't use the "everyone knows" argument, I've tested every lens I own, which is about 50. I test them at 4-5 different apertures, I examine the film under my Leica GZ6E stereomicroscope, and by making prints. I test glass versus resin versus polyester filters for their affect on sharpness, Carbon Fiber versus aluminum versus wooden tripods for vibration dampening, slower shutter speeds and the affect of the shutter vibration on longer lenses, the affect of vibration in copal 3 versus copal1 versus copal 0, the apertures required to overcome the varying degrees of film buckling in 6x6,6x7,6x8,6x12 and 6x17 cameras, I use a second laser aligner to check the calibration of the first laser aligner, simply put I don't leave anything to chance, assumption or hearsay.
Not trying to be insulting but one's work is an excellent reflection on their technical competence and skill levels, and in spite of your seeming to read a great deal, your work does not reflect high standards of technique, and whether you may know obscure optical formulas or not, it's hard to fake the quality of one's work. To be blunt if your work were better I'd put a lot more credibility in your comments. And yet you come on a forum and spew misinformation to the degree that you often do, it is a disservice to those who come here seeking reliable and accurate information and are making a serious effort to better their skills.
Btw regarding your circle of confusion question, you also need to determine what size the print is going to be as final reproduction size and viewing distance changes the requirements for what is acceptable circle of confusion. But what do I know, I don't claim to be a scientist, just a photographer. What do you claim to be?
Not trying to be insulting but one's work is an excellent reflection on their technical competence and skill levels, and in spite of your seeming to read a great deal, your work does not reflect high standards of technique, and whether you may know obscure optical formulas or not, it's hard to fake the quality of one's work. To be blunt if your work were better I'd put a lot more credibility in your comments. And yet you come on a forum and spew misinformation to the degree that you often do, it is a disservice to those who come here seeking reliable and accurate information and are making a serious effort to better their skills.
Btw regarding your circle of confusion question, you also need to determine what size the print is going to be as final reproduction size and viewing distance changes the requirements for what is acceptable circle of confusion. But what do I know, I don't claim to be a scientist, just a photographer. What do you claim to be?
Interesting tactic here... "*I* don't like your work, so you are spewing misinformation". I can't think of anything even remotely resembling an intelligent reply to that one. Anyone out there sense something like a cheap shot here?
Not true. "Circle of Confusion" has nothing to do with "perception". It is the distance where two distinct points are presented as two distinct points (anyone involved in telescope lenses will recognize this as "resolution"). In camera lens discussions among the photographic community, "resolution" is more commonly described as "lines per millimeter". It has NOTHING to do with tripods, print size, "final reproduction size" (there is a difference between these two?), viewing distance, or - like that. It is a vital factor in lens DESIGN, not what happens later.
Correct me if I am wrong, but didn't you claim to know a vastly greater amount more about "diffraction", and "diffraction limiting", than I did?
A once qualified (probably still am) Quality Assurance Specialist, trained and employed in a company specializing in "state-of-the-art" (I hate that phrase - substitute, "wild, way out there") Optical Systems. My specialty was the Optical-Mechanical interface. Later, in another company, Optical Tooling and Calibration Lab Manager.
Other than that, a human being with a nearly obsessive interest in Photography and Optics... and a fair to middlin' Flycaster.
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I have a comment on the idea that grain looks sharper when a lens is closed down. If an enlarger has a bright enough bulb the grain focuser can be difficult to use with the lens wide open. This can be due to several things other than diffraction. If an enlarger is not perfectly aligned then closing down a little can at least make things look more even. Too much light coming through the negative can also make the view through a grain focuser look low in contrast. When the Olympus OM system came out its lenses were tested against comparable Nikon lenses. Some of the Zuiko lenses had very high contrast but lower resolution than the Nikkors. The OM cameras also had very bright viewfinders and some reviewers found the slightly dimmer Nikon viewfinders to have more apparent contrast.
You can improve your final image a lot more by using a plain Jane enlarging lens with a medium format negative than by using an apo enlarging lens with a 35m negative.
You can improve your final image a lot more by using a plain Jane enlarging lens with a medium format negative than by using an apo enlarging lens with a 35m negative.
There are many photographers who's work I don't like but who's technical ability I have to respect, your technical ability does not give me any cause you view as being even remotely technical competent. Not a cheap shot, just being brutally honest. As for your comments, you have a far higher opinion of yourself than your work justifies, the vast majority of your comments are not based on fact or actual first hand experience but are based on conjecture and bravado.
There is knowledge based on theory and knowledge based on actual experience or practical usage, while no one can deny that you are well read ,you have a complete lack of any practical experience of value as a photographer. While your criteria for circle of confusion is based on formula and theoretical uses, many of which I first learned 30 years ago and then forgot as theory has little use in practical application, any photographer working in the field cares about circle of confusion in a more immediate sense, " at what point of enlargement or reproduction ratio will people perceive my image as being soft or out of focus?" I carry a software program in the field that enables me to determine COC based on neg size,print size and aperture. This link goes to a page for a COC calculator that better explains the relationship between COC, DOF as they relate to print size and visual perception.
Dead Link Removed
As for diffraction I'm sure you must know the formulas for calculating it far better than I do, yet I have enough sense to not use an enlarging lens stopped down to f 32
Dinesh, Take those off and give them back to the nice lady.
What did you find? My own fairly casual tests (fine grain film, high quality lens, test charts) found no detectable difference until I tried 3mm window glass. Ctein, a better experimentalist than I, found the same. It sounds as if you have tested fairly extensively and I'd be interested to hear your results.
Cheers,
Roger
Dear Ed,
Yes, that's one way of defining it (there are others, but all have broadly the same consequences), and this is what you get on the film. Enlarge this image, and the whole concept does indeed depend upon print size and viewing distance. Don't blow it up very far, or look at it from further away, and it'll look sharp. Blow it up more, or look at it from closer, and it'll look less sharp. Those formulae for 'circle of confusion' which relate it solely to focal length are of extremely limited use.
Taking the 'lp/mm' argument, let's take 80 lp/mm on the film as a realistic ficgure: I have seen 100 lp/mm often enough, centrally, with the best lenses, and 125 lp/mm occasionally, but the latter is not usually repeatable because the film is rarely located accurately enough.
Now let's take the resolution of the eye. At 'normal viewing distances', often taken as 25cm/10 inches, Ctein's estimates for 'sharp' run from 5 lp/mm ('sharp enough for many purposes') to 30 lp/mm ('vernier resolution, the ability to see a discontinuity in a line'). I work on 8-15 lp/mm (he and I have discussed this, as you might guess, though it was some years ago and I apologise to him if my memory is at fault). Let's take 10 lp/mm for a round number.
Let's also assume a perfect enlarging lens, because it makes the sums easier; in reality, of course, there will always be some degradation.
Any enlargement of 80 lp/mm up to 8x will give 10 lp/mm or better, or 'sharp'. Any enlargement over 8x will give less than 10 lp/mm or 'unsharp'. Now double your viewing distance, and you can enlarge 16x for 5 lp/mm but it will look just as sharp -- until you go back to the old viewing distance.
I really am having some difficulty in understanding your assertion that the desirable size of the circle of confusion is not, as Earlyriser suggests, dependent on print size and viewing distance.
You might accuse him of technical obsession and not caring enough about the picture; he might accuse you of being sloppy. As long as the pictures speak for themselves -- and de gustibus non disputandum est -- you'd both be wrong. If you both made rotten pictures, you'd both be right.
Cheers,
Roger
Roger were you and Ctein using a microscope to examine the film? I found that with longer focal length or telephoto lenses the only way to go is glass, that the plastic filters cause a noticeable loss of sharpness, no need for a microscope on this one. you can see the difference on an 8x10 print. The longer the lens the worse the degradation. I'm surprised you didn't know about this one, I thought it was fairly common knowledge.
The thicker plastic filters have an edge in plano parallelness but higher thickness also seems to shift focus slightly more, and I would suggest checking focus with the filter in place. The thin filters seemed to have less of a focus shift but required something to hold them more rigidly as they can curve. Both the thick and thin plastic filters have issues regarding being plano parallel to the lens as they are usually in slip in filter holders and are often not parallel to the lens. Using normals or wide angle lenses you would not notice much of a difference. However if you do carry and use teles/longs, then you need to use glass filters, and as long as you're carrying glass filters for your long lenses you might as well use them on everything.
One of the things that made plano parallelness more obvious to me was the use of filters during enlarging. I used to add and subtract various diffusers while printing and noticed not just a diffusion affect but a stretching of the grain at the edges of the print and increased bluriness, more so towards the edges, the more often the filters were swapped on and off during the different contrast (split filtering) exposures. ( I might use a diffuser during the magenta exposure but none during the yellow, etc) I then decided to have my grain focuser lock in on some tiny speck that was obvious. Through the grain focuser a box is visible, I would put that speck on the corner of the box and then add or remove filters, the speck would move all over the place. Now when I do split diffusing, during the non diffusing exposures I add a haze filter to the yellow exposure to substitute for the added glass of the removed diffuser filter, the replaced glass seems to keep refocusing that speck into the same place. I also found that wider angle enlarging lenses had more of the stretching issue than longer enlarging lenses.
I also tested various shutters at various speeds and the intuitive guess that the larger the shutter the more the shutter vibration is correct. Using telephotos, as they tend to exacerbate vibration problems I tend to use them for any kind of vibration testing, I found that at the same speeds, like the 1/4, 1/8, 1/15 range, the smaller the shutter the better the result. The worst offender being the Sinar Auto Aperture shutter which I consider useless for out door work because it's vibration problem was severe. ( a pity though because I own 2 of them and at the time all of my lenses were on DB mounts, I have since converted nearly all my lenses to copals)
I have been curious about whether multi coated lenses, in which the front element has a substantial curve, would have less flare if a high quality multi coated filter were used. My assumption is that multi coating causes what would be considered stray, flare inducing light, that is light hitting the coating from an angle to be reflected. With a flat filter, light hitting the coating dead straight, that is 90 degrees to the coating on goes through with little loss, little coming from progressing angles get increasingly reflected. With a curved lens surface, the curve makes for a huge area in which the 90 degree to the coating follows the curve and creates a far larger angle for stray light to not be reflected by the coating. This is all conjecture on my part and may not show on any kind of tests and may be a non issue. Obviously using a multi coated haze or skylight filter alters the color and makes any test results useless. However I have bought a rodenstock protective filter, allegedly coated with the same rodenstock coating used on their lenses, and without any filtering aspects, for me to test.
What is ironic about all of this testing, is that for a great many of my images, all I'm going to do is print the image through a crappy diffusion filter anyway.........
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Dear Earlyriser,
As far as I recall, we both used standard lenses; your point about focal length is well taken, and I shall now try it for myself (not because I don't trust your results, but to see exactly what the effects are). Yes, we both used microscopes. At least, I did, and I assume he did. Thanks.
Cheers,
Roger
As far as I recall, we both used standard lenses; your point about focal length is well taken, and I shall now try it for myself (not because I don't trust your results, but to see exactly what the effects are). Yes, we both used microscopes. At least, I did, and I assume he did. Thanks.
Cheers,
Roger
Roger, use a lens at least 2x the film diagonal for your tests. Also if you need the scientific explanation the owner of filter connection can give you the science behind the phenomenon.
It's not about being technically obsessed, it's about having an understanding of the chemical and mechanical aspects of our work that ultimately affect our work. The tools have always had importance to the artist, they are the physical conduit for our creativity and traditionally the very first thing an artist had to do was master their technique. Once that was mastered they were free to do whatever they could imagine as they had the necessary tools to do anything.
I also agree that the work speaks for itself, and is the best indicator of whether someone just talks the talk, or walks the walk.
It's not about being technically obsessed, it's about having an understanding of the chemical and mechanical aspects of our work that ultimately affect our work. The tools have always had importance to the artist, they are the physical conduit for our creativity and traditionally the very first thing an artist had to do was master their technique. Once that was mastered they were free to do whatever they could imagine as they had the necessary tools to do anything.
I also agree that the work speaks for itself, and is the best indicator of whether someone just talks the talk, or walks the walk.
Ole
Moderator
The thing with filters is that a perfect filter would be perfectly flat and planoparallell.
but since real objects are never perfect, we have to decide on some point that is "near enough to perfect". And that point varies with the application: There's a big difference in using 8x10" slides at $30 a shot, or using a 35mm point-and-shoot for holiday snaps!
so what happens if the two surfaces of a filter are not perfectly parallell? simple: It gets a focal length. A very long one, and it usually varies across the filter too, and can be positive, negative, or both (not in the same place, though).
From the basic optical formula for adding lens components (1/F = 1/F1 + 1/F2) we see that if F1, our camera lens focal length is very short - say 100mm - then the addition of a 10000mm F2 filter focal length matters very little. But if you're using a very long lens, like 1000mm, that same filter would make a large and significant difference in the focal length of the whole system. All the lens optimisations would go straight out the window as well, since the filter isn't optimised to be anything but neutrally flat.
So you shouldn't just pick a lens of at least 2x film diagonal, you should pick the longest lens that it's at all possible that you might want to use on that film format.
but since real objects are never perfect, we have to decide on some point that is "near enough to perfect". And that point varies with the application: There's a big difference in using 8x10" slides at $30 a shot, or using a 35mm point-and-shoot for holiday snaps!
so what happens if the two surfaces of a filter are not perfectly parallell? simple: It gets a focal length. A very long one, and it usually varies across the filter too, and can be positive, negative, or both (not in the same place, though).
From the basic optical formula for adding lens components (1/F = 1/F1 + 1/F2) we see that if F1, our camera lens focal length is very short - say 100mm - then the addition of a 10000mm F2 filter focal length matters very little. But if you're using a very long lens, like 1000mm, that same filter would make a large and significant difference in the focal length of the whole system. All the lens optimisations would go straight out the window as well, since the filter isn't optimised to be anything but neutrally flat.
So you shouldn't just pick a lens of at least 2x film diagonal, you should pick the longest lens that it's at all possible that you might want to use on that film format.
Ole thanks for the formula, I suggested that Roger use at least a 2x lens because I wanted to give him a practical focal length, but yes the problem becomes more apparent the longer the lens. I was also assuming large film format, hence bigger focal lengths.I think ultimately we need to test this out on the Hubble space telescope. Talk about a telephoto!!!
Dear Ole,
And indeed this is one of the reasons I'd never had a problem. I very seldom use anything longer than 2x film diagonal (90mm on my Leica, 300mm on 4x5) and indeed I use a lot of wide-angles or at most 'long standard' lenses (210mm on 4x5), which would explain a good deal of why I have never found any but the worst filters to impair definition.
Thanks for a brilliantly simple summary of how the filters degrade image quality.
Cheers,
Roger
Dear Roger,
If you will recall, the subject was "Diffraction Renders Use of Small Apertures Useless (or at least highly udesireable) In Enlarging" - a concept I took issue to - with. Someone here (who I shall not name) made the statement that I knew *nothing* about diffraction. Now, that person says, "Well, yes, I remember something about calculating "diffraction limits" ... but that is not relevant here... because there are *many* things that affect print quality.
Of COURSE there are many things that affect print characteristics ... but that is really a change of subject - trying to divert the attention to something else, other than the original qestion - DIFFRACTION.
Do you agree that "I know noting about optics" - and that is proven because Earl... - whoops - Has determied with "BRUTAL HONESTY (no "opinion" here) tht my work is "totally BAD"?
Dear Ed,
My knowledge of your knowledge of optics (if you will forgive the convoluted sentence) is non-existent; I can only judge from what you post. I stand by all I've said in this thread -- that yes, I could see the difference caused by diffraction, but probably not in many 'real world' pics rather than test charts, and that circle of confusion must be related to degree of enlargement and viewing distance.
Anything much more than this is just chest-beating and doesn't help any of us to learn or teach anything -- such as what I have learned about focal length and filter quality.
Cheers,
Roger
My knowledge of your knowledge of optics (if you will forgive the convoluted sentence) is non-existent; I can only judge from what you post. I stand by all I've said in this thread -- that yes, I could see the difference caused by diffraction, but probably not in many 'real world' pics rather than test charts, and that circle of confusion must be related to degree of enlargement and viewing distance.
Anything much more than this is just chest-beating and doesn't help any of us to learn or teach anything -- such as what I have learned about focal length and filter quality.
Cheers,
Roger
Uh .. "parallel" is really not the characterisic ... If both sides are, in fact, FLAT, there will only be a shift in image placement. If either surface is not flat, you are right... there will be a "focal length."
I once tested a "Navigators Window" from a B17. Both surfaces were acceptably flat, but non-parallel by 28' (minutes) - enough to cause serious errors in navigation.
Good to see you here, Ole. Do you remember our discussions about "diffraction"? Somewhere here, I have the addresses of the web sites you discovered .... If I could only find them.
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