Resolution Limits of 35mm Photography

DrPablo said:

All manufacturers publish it in their MTF charts. You see lens resolution peak at a certain aperture (often f/8 or f/11 for 35mm lenses), beyond which resolution progressively decreases with narrower apertures.

Click to expand...

... And where do we determine that this effect is invariably - and only - caused by diffraction?

A lens is DESIGNED for optimum performance under certain circumstances. Fast 35mm lenses "peak" at larger apertures (the assumption is that they will be used more frequently at larger apertures and in low-light situations than slower lenses) - NOTHING - at all to do with "diffraction". Enlarging lenses are designed to give optimum performance in the middle of the aperture range - but they CERTAINLY do not "go to hell" at the extremes, either... and neither do cameara lenses from any of the reputable manufacturers.

Of all the concerns I have when photographing, using a lens to the limits of its design is going to be the least.

I have the Carl Zeiss Planar 2.8/80 T* - S/N 7210829 on one of my 'Blads at the moment. I also have the MTF charts. Can anyone tell me where this lens is "Diffraction Limited"?

The Nikon D2X(s) has the highest number of pixels per millimeter and is only 180 pixels per millimeter. The Canon 1Ds Mark II with full size sensor is 138 pixels per millimeter. Of course pixels per millimeter is not the same as lines per millimeter but it simply can not have a higher lpm rating.

Snapshot
Resolution the lens is capable of and lens “sharpness” does not have many things in common. That term “sharpness” does not have meaning and it is actually a vague term, it means actually lens acutance. This is, simple, distance between light and dark portion of the edge and is controlled by lens design, accuracy of production and assembly, kind of glasses,….
That 200 lpm resolution I would rather assign as important to painting, airbrushing,… not to photography. One of property of photography is not high resolution but rather blur. This is quality that no other medium have, it belongs to photography only. However this means blur controlled by photographer (lens opening, developer, film) not produced by bad lens design.
Do not be tricked by lens manufacturers. Leica, Rodenstock, Schneder, Nikon, Canon,… they all make very good lenses that can give honor to any photographer, just need to learn how to use it.
I like to say how good is Nikkor 1.4/85d lens. Just recently I had shooting people portraits on snow included into picture. This lens in such condition will flare (and if you like will give “low resolution picture”), so Leica summicron (or Nikkor micro 2.8/55) was my choice. This is how it works when you know your lenses. Lens resolution, when you stick to lens maker listed above, is not something to be concerned about. Good lens maker knows very well what photography need, and job of photographer is not to think about lens design but how to use the lens to achieve the goal.
Have a nice photo day

www.Leica-R.com

Ed -- I'll link you some reading on the subject. This article explains very well how the theoretically perfect lens appears on an MTF curve, and how that differs from an imperfect lens. Much is as I've explained above, but it may be more helpful when you see the graphs.

http://www.bobatkins.com/photography/technical/mtf/mtf2.html

Of all the concerns I have when photographing, using a lens to the limits of its design is going to be the least.

Click to expand...

Well, I don't think it's hard to operate within the strengths of a lens, and I also don't think it's wise to dismiss these factors. This is particularly true for 35mm shooting. I mean why would you stop down to f/32 on a 35mm camera if you're focusing on the moon? All you'll do is limit lens performance by stopping down out of proportion to your DOF needs.

Chan Tran said:

The Nikon D2X(s) has the highest number of pixels per millimeter and is only 180 pixels per millimeter. The Canon 1Ds Mark II with full size sensor is 138 pixels per millimeter. Of course pixels per millimeter is not the same as lines per millimeter but it simply can not have a higher lpm rating.

Click to expand...

LPM is line pairs per mm, i.e. the ability to resolve two separate lines from one another. So when calculating that on these DSLRs, lines per mm is actually 1/2 the pixels per mm, because it takes two pixels to distinguish two details. Thus, the D2X is about 89 lpm and the 1DsII is about 79 lpm.

DrPablo said:

Ed -- I'll link you some reading on the subject. This article explains very well how the theoretically perfect lens appears on an MTF curve, and how that differs from an imperfect lens. Much is as I've explained above, but it may be more helpful when you see the graphs.
http://www.bobatkins.com/photography/technical/mtf/mtf2.html

Click to expand...

Thank you for the link, Dr. P.

I haven't really had chance to grind fine on this article...

I understood what was being written here. My comments now, after more or less of a quick scan, are the same: It is something of a bizarre/ strange way to consider the quality of a lens, and it certainly would NOT deter me from using a lens throughout the entire aperture range.

Technically, my first, knee-jerk comment would be that I have to study the effect of what is essentially a survey of the opinions of many people to establish the factors involved in "Subjective Quality". I remember when that bastion of optical engineering, Pop Photo, first started using that term - and it had NOTHING to do with Modular Transfer Function charts.

Back to "resolution" ... I will in the future (going to be difficult to continue to be motivated here) study that article.

Let me illustrate what I mean by "A strange way": Some time ago, one of the participants here wrote that "We had it all wrong - depth of field was NOT determined by f/stop, but by shutter speed."
I disagreed. His response was that, "When you use a slower shutter speed, you get more depth of field ... how is it possible to disagree?" I wrote, that, of course when you increase the time of exposure, all conditions being the same, the aperture size must be decreased ... and that the aperture is the primary factor in determining depth of field. Again he wrote ... "No, no ... that is only a secondary effect - and the aperture really means nothing. - or very little".
Nothing I could argue had any effect on his line of thinking... in his framework, Slow shutter speed = Greater depth of field = TRUE... but in mine, not entirely, and certainly not exclusively.

Diffraction, at some point, WILL affect the image quality of any lens. That effect is gradual ... there will be *very little* diffraction at large apertures, and its effect is not linear. The question really is, "When is diffraction severe enough to be unacceptable?"

Modular Transfer Charts are indicative of the performance of a lens ... considering *many* factors other than, AND including diffraction effects. This article suggest something of, "That is a beautiful Dog's tail. Based on that, the inference is that there must be an beautiful dog at the other end."

Now ... from a PRACTICAL view... How is the information in this article to be used? Is it a good idea to lock every lens we own at one aperture -- that which gives the "best" performance? Is it advisable to remove the iris diaphram so commonly in use and replace them with one fixed aperture?

In my book, it is not. I NEED more flexibility - even at the cost of slightly - **VERY slightly** less - inconsequentially less - than "absolute best" performance.

Oh, BTW ... Are there any examples of a lens manufacture describing a lens as, "Diffraction Limited at f/8" ? .. or wherever?

Now for breakfast - and rest for my brain.

Ed Sukach said:

His response was that, "When you use a slower shutter speed, you get more depth of field ... how is it possible to disagree?" I wrote, that, of course when you increase the time of exposure, all conditions being the same, the aperture size must be decreased ... and that the aperture is the primary factor in determining depth of field. Again he wrote ... "No, no ... that is only a secondary effect - and the aperture really means nothing. - or very little".

Click to expand...

Well, people can be obstinate but that's not a hard one. You can hold shutter speed constant, ISO speed constant, vary the aperture, and vary the ambient lighting in response to the different exposure requirements. So the only variables would be lighting and aperture, and they would be modified reciprocally. Obviously you'd be able to demonstrate a close relationship between aperture and DOF that controls for shutter speed -- and he couldn't argue that it's really ambient lighting that controls DOF, because you've accounted for that in your exposure.

The question really is, "When is diffraction severe enough to be unacceptable?"

Click to expand...

Well, sort of. The real question is "What kind of lens resolution do I require?" That is contextual, and it has to do with your format size, enlargement factor, and acceptable viewing distance. If your desired output is an 8x10 contact print viewed from 1 foot away, then you can get away with a lot more diffraction than if you're enlarging a Minox shot to 30x40 inches.

Now, clearly demonstrable is that lens resolution will peak at a certain aperture, and it will fall progressively beyond that aperture. I'd be surprised if you could find an MTF or lpm test that shows f/32 resolves better than f/11 (with a flat subject).

So why would a lens resolve less at narrower apertures if not diffraction? Why would even the best lenses out there, some divinely blessed noctilux or something, still hit a resolution limit beyond which resolution falls with narrowing aperture? I don't have enough background in optics to tell you exactly why one should believe that it's diffraction as opposed to anything else, but surely these narrow apertures will only further negate intrinsic lens flaws. So it stands to reason that the easily observed resolution limit, which becomes progressively lower with narrowing apertures, are indeed attributable to the aperture itself.

DrPablo said:

So why would a lens resolve less at narrower apertures if not diffraction? Why would even the best lenses out there, some divinely blessed noctilux or something, still hit a resolution limit beyond which resolution falls with narrowing aperture?

Click to expand...

Some lenses resolve MORE at smaller apertures.

Again... Diffraction is not the ONLY reason affecting the resolution of an lens. Additionally, resolution itself is not the sole "test" of a lens/ optical system. From memory, all the MTF charts I have seen take contrast into consderation as well - there are also abberations, chromatic correction errors, coma (caused by centering errors) ... and ... this could easily encompass all the material in a Theoretical Optics class.

I'll ask again... what is the practical application of this "point where the resolution is affected (beyond its inherent defects) by diffraction" information? - and who includes this in the specifications for the lens?

One could have an abyssmally poor lens ... and it remains abyssmally poor to the point where it worsens even more due to diffraction. Interesting ... but..

That was another characteristic I noticed in that article ... the emphasis of the effect of diffraction on a "perfect" lens. True, but in the real world there are NO "perfect" lenses... each and every one is a collection of design compromises. While diffraction is interesting, it pales - badly - in importance to the other concerns affecting the photographer.

DrPablo said:

Now, clearly demonstrable is that lens resolution will peak at a certain aperture, and it will fall progressively beyond that aperture.

Click to expand...

True... but are you saying that the ONLY possible reason for that is "diffraction"?

I'd be surprised if you could find an MTF or lpm test that shows f/32 resolves better than f/11 (with a flat subject).

Click to expand...

Are we limiting the field of interest here to common camera lenses or can we include process and other "specialty" lenses?

I can remember working with the really, really large cameras used to photograph masters and reduce the images to printed wiring board size... focal lengths of ~ I don't know, five or six feet - installed through the wall of a "darkroom", where the light-sensitve "film" was processed. These had no diaphrams and the fixed f/stop WAS on the order of f/32 - and those lenses were designed accordingly. Of course, with those parameters, there was very diffraction involved.

Ed, the SQF that Pop Photo uses was invented at EKCo and is very closely related to MTF. The choice of the word "subjective" for a repeatable well defined measurement is unfortunate.

If you look at MP's SQF charts for lenses made for 35 mm cameras, you find that no lens for a 35 mm camera produces 35 mm negatives that will produce high quality prints much larger than 8" x 10". And none of them does nearly that well at small apertures. There are a couple of messages there.

Ed Sukach said:

One could have an abyssmally poor lens ... and it remains abyssmally poor to the point where it worsens even more due to diffraction. Interesting ... but..

Click to expand...

Think of a pinhole. A 10mm pinhole at 50mm from the film plane is an abysmally poor 50mm lens at f:5.

As you decrease the size of the pinhole the image gradually sharpens, since you reduce the "aberrations" introduced by having no lens at all. At around 0.1mm it actually produces a fairly decent image (f:500). If you decrease the pinhole diameter even further, you will get a gradually softer image - even pinholes have an optimum aperture!

Dan Fromm said:

Ed, the SQF that Pop Photo uses was invented at EKCo and is very closely related to MTF. The choice of the word "subjective" for a repeatable well defined measurement is unfortunate.

If you look at MP's SQF charts for lenses made for 35 mm cameras, you find that no lens for a 35 mm camera produces 35 mm negatives that will produce high quality prints much larger than 8" x 10". And none of them does nearly that well at small apertures. There are a couple of messages there.

Click to expand...

Interesting. When did Pop photo first start to use "Subjective Quality" Tests?

As I remember them, from 'way back in the distant mists of my memory, it was late '60s/ early '70s -- before MTF testing was really in place. My most severe critique of those tests was that they involved evaluating images made on film, rather than the aerial images I was struggling with via microscope and optical bench.

Is it possible that there was some sort of band-aid "healing" process applied after the fact?

Ed, your memory is failing. PP introduced their SQF tests in the late '80s.

And your judgement's gone too. The only way to find out what a lens will do for you is to shoot it, using the emulsion(s) you normally use, at the ranges of apertures/magnifications you typically work at. Otherwise all you're doing is, um, abusing yourself.

No, no cheating after the fact.

The SQF is really a clever idea and a very good way of summarizing what a lens will do for the user. I.e., how big an acceptable print can be made with it. I don't know whether EKCo still has a fair number of very bright people who think hard about what photographers do and value, but at one time they had a fine group of 'em indeed.

I don't think it would be a useful specification for lens manufacturers to expressly publish their diffraction limit for a few reasons.

First, it's fairly similar among all lenses on that format at that focal length.

Second, it's easily derived from MTF data.

Third, it's not something that directly translates to your practice when using the camera in the field. I mean it's well and good to have an f/11 diffraction limit when shooting a flat target. But when you have critical detail that requires a huge depth of field, you have to operate past the diffraction limit anyway if you want it all in focus.

Dan Fromm said:

Ed, your memory is failing. PP introduced their SQF tests in the late '80s.
And your judgement's gone too.

Click to expand...

Thank you for your thoughtful comment.. I will, however, refrain from replying in kind.

The only way to find out what a lens will do for you is to shoot it, using the emulsion(s) you normally use, at the ranges of apertures/magnifications you typically work at. Otherwise all you're doing is, um, abusing yourself.

Click to expand...

Well, I will suggest, through this fog of "deficient" judgement, that the first rule of measuring anything is to to simplify - to eliminate all possible factors that will cloud the results -- to know WHAT you are measuring - and as far as possible measure ONLY that. When you introduce something else into the equation, the accuracy and precision of the results are called into question: Was the lens really that poor as far as resolution, or was the film actually not flat; was the film capable of only less resolution than the lens ... was the film defective in some way ... ???

Optical bench testing of the LENS should only scrutinize the characteristics of the lens itself - not combined with 14 other factors in a complicated system, all at once.

If "PP' only introduced tests labeled "SQ ..." something in the late '80s someone else had to precede them. By then, I was into Metrology Laboratory/ Standards work and not quite so intensely interested in lens testing and optical bench work.

The SQF is really a clever idea and a very good way of summarizing what a lens will do for the user. [/QUOTE]

I'd comment - but why? You have already blown me off - so what would be the point?

.. I.e., how big an acceptable print can be made with it.

Click to expand...

Still, I feel compelled to ask - Who is doing the "accepting"?

I don't know whether EKCo still has a fair number of very bright people who think hard about what photographers do and value, but at one time they had a fine group of 'em indeed.

Click to expand...

We have one of the "bright ones" participating here - Photo Engineer.

Unfortunately, I can't say the same about present "Big Yellow" top management.

Ed Sukach said:

Still, I feel compelled to ask - Who is doing the "accepting"?

Click to expand...

Ok, this gets down to physiology. The human retina, based on the spacing of our cones (our highest acuity photoreceptive cells) in the fovea (the highest acuity part of our retina and the center of our visual field), is able to resolve about 7 to 10 lpm of a well lit high contrast subject from a 10 inch viewing distance. Thus, for something to be sharp and have critical fine detail, it has to at least match if not surpass the physiologic limit of our own retinas' resolution. So the goal is to have at least 7 to 10 lpm for a print viewed from 10 inches, 3.5 to 5 lpm for a print viewed from 20 inches, etc.

If a lens can resolve 50 lpm (on a film that can record 50 lpm), then you have around 7 linear enlargements before the detail density of a print drops below 7 lpm. This, naturally, is because an enlargement will increase the spacing between details but not increase the actual amount of detail.

From 35mm and a 50 lpm lens, a 7x enlargement gets you a 6.5 x 9.8 inch print that still has at least 7 lpm (or let's just say 8x10, because it's pretty close).

So if you have a 35mm lens capable of resolving 70 lpm, and because of your "protective" UV filter and f/32 aperture actually resolve only 40 lpm, you're going to have to stand a full 2 feet away from a modest 11x14 print for it to look truly sharp. On the other hand, if you use a good lens at its sweet spot and resolve a good 80 lpm, you can actually print twice as large (or view the 11x14 from twice as close) and maintain critical sharpness.

If you shoot with an 11x14 view camera, on the other hand, and use an antique uncoated lens with grime and fungus and you stop it down to f/90, you will still have a sharp 11x14 print from under 10 inches even if your crappy mold-besotten lens resolves only 25 lpm, because you're not enlarging it.

Ed, I've blown you off because you're committing two sins.

First, you're trying to conduct a technical discussion in a medium -- the on-line bulletin board -- that is not conducive to technical discussions. You're asking people to type a book for you. The book you want is John Williams' Image Clarity: High-Resolution Photography. Do us all a favor and buy a copy.

Second, you're being obsessive about one component, the taking lens, of the system that produces images that can be looked at. If it is any consolation, you're not alone in this sin. Thing is, what matters is system performance, not the performance of any one component. And the taking lens is rarely the limiting component. Not only that, sharpness is just one of the elements that can help an image please, and since there are tradeoffs between sharpness and other elements of the image sharpness need not always be paramount.

Now go back under your bridge and stop molesting aerial images and goats.

DrPablo said:

Ok, this gets down to physiology...

Click to expand...

Tell me ONE thing ... WHY do some people think you DON'T understand when you simply dasgree, or wish to view a question from an alternate point? WHY???

I've got it.
I had it when I read the article.
I understand each and every word about the perceptual modification to the Modular Transfer Function.

IN MY HUMBLE (note the emphasis upon HUMBLE) OPINION, the only acceptance of any importance is up to the photographer. If she/he chooses to make a photograph with blurred, diffusely defined properties, (see portraiture for one example) it is FINE with me.

That is deep in the field called "aesthetics". Do you think a rational discussion of asethetics is possible?

Dan Fromm said:

Ed, I've blown you off because you're committing two sins.

Click to expand...

And you think that another opinion - differing from yours is a "sin"?

First, you're trying to conduct a technical discussion in a medium -- the on-line bulletin board -- that is not conducive to technical discussions. You're asking people to type a book for you. The book you want is John Williams' Image Clarity: High-Resolution Photography. Do us all a favor and buy a copy.

Click to expand...

You haven't been on APUG very long - have you.

This is not the first "technical discussion" ever - nor the most complicated. You might want to revisit the discussion (remember it, Ole?) about diffraction itself.

Second, you're being obsessive ....
... you're not alone in this sin.

Click to expand...

Here we go - a psychological analysis and moral judgement.

And the taking lens is rarely the limiting component. Not only that, sharpness is just one of the elements that can help an image please, and since there are tradeoffs between sharpness and other elements of the image sharpness need not always be paramount.

Click to expand...

I've been re-reading my posts. not only my "judgement" has gone to hell, but my ability to find anything where I have disagreed with that statement has as well.

Now go back under your bridge and stop molesting aerial images and goats.

Click to expand...

Smooth. An indelible indication that I am striking a nerve. Only those insecure enough not to offer intelligent resort to insults.... the last refuge of a coward.
Calm down .. I did not enter this - or wish it to continue it as a "Win-Lose" contest.

BTW - I would really like to see some of your work.

Dan Fromm said:

You're asking people to type a book for you. The book you want is John Williams' Image Clarity: High-Resolution Photography. Do us all a favor and buy a copy.

Click to expand...

Sorry for the delay ... I was unavoidably distracted.

All those insults - and now you want a "favor" from me?

I would suggest another book - one that was used a a primary textbook in my training...

"What is light?" by A. C. S. van Heel and C. H. F. Velzel

Be advised, though ... one should have an I.Q. somewhat larger than their hat size to get the most out of this text.

Ed Sukach said:

Tell me ONE thing ... WHY do some people think you DON'T understand when you simply dasgree, or wish to view a question from an alternate point? WHY???

Click to expand...

Ed, I never assumed you didn't or wouldn't understand.

You're the one who asked the question Who is doing the "accepting" in reference to an acceptably sharp print. So both for your and perhaps everyone else's benefit, I explained why there really are quantifiable characteristics of a print that will look sharp. If by acceptable you mean to make an aesthetic argument (rather than an optical one), then I don't see what place that has in a discussion over diffraction.

The endpoint of a discussion on lens diffraction and why it should bother you is a matter of detail transmission and print sharpness. It's not a question about beauty. Insofar as sharpness is requisite to many photographers in the quest to create a beautiful print, then it is germane to discuss how sharpness may be best achieved.

I'm sorry I'm not considered "one of the bright ones" in your book, but I've done nothing other than tried to articulate my understanding of your question.

If you really have to ask endlessly repeating "But why?" questions, simply because you are unwilling to accept what you're told without proof, then you're looking in the wrong place by asking it on a forum. You will never get your answer here to your satisfaction. You can skeptically question optics all the way back to the laws of physics and the origins of the universe if you want.

I'd suggest you look in any number of textbooks on the subject to get your answer. I'm not even sure that will help, because it's not primary literature, so you may need to stop by Cambridge, visit the archives in the MIT library, and look up the original journal articles that define our understanding of optics. And then report back to us, because I'm honestly interested in this stuff and wouldn't mind a more robust understanding than I already have.

Beyond that, as Descartes might have said, everything we think we know might just be a big cosmic joke, and the only thing we can be completely sure of is that we exist.

Now, I've been nothing but nice to you in this thread, and have discussed this topic to the best of my understanding out of shared interest. Clearly either your background in optics, your inherent cynicism, or both make you not accept what I write. That's fine, I mean I have my own area of academic expertise that would not be that swayed by a lay-discussion. But you've personalized this to such a degree that I'm really not enjoying it anymore. I hope you get your answer.

Sorry, Ed, I don't have a digital image capture device of any kind, including a scanner. Even if I did, I'm one of the non-paying parasites that afflicts APUG.org so I can't post digitized images here.

What does the quality of the pictures I take have to do with how well I understand the technology?

I don't know if you're aware of it, but I have sold lenses on eBay and have put digitized images in my listings. One of those images was a full frame scan of a 6x9 transparency, done for me by a local lab; all of the others were done with borrowed digital point & shoots to which I no longer have access. I'm not anti-digital at all, just don't do it.

DrPablo said:

Ed, I never assumed you didn't or wouldn't understand.

Click to expand...

Sounded that way to me. Why (sorry for that ..) would you re-post the information in the article, then?

You're the one who asked the question Who is doing the "accepting" in reference to an acceptably sharp print. So both for your and perhaps everyone else's benefit, I explained why there really are quantifiable characteristics of a print that will look sharp. If by acceptable you mean to make an aesthetic argument (rather than an optical one), then I don't see what place that has in a discussion over diffraction.

Click to expand...

Well -- again I will disagree - not with the purely technical structure ... but that there is some set, concrete method of determining "acceptabilty". Who wrote the "law" that any amount of "sharpness" was a necessity?

The endpoint of a discussion on lens diffraction and why it should bother you is a matter of detail transmission and print sharpness. It's not a question about beauty. Insofar as sharpness is requisite to many photographers in the quest to create a beautiful print, then it is germane to discuss how sharpness may be best achieved.

Click to expand...

Ah ... "Why it should bother me..." -and it DOESN'T!! Why (here I go again) should my reliance on the expertise of the lens manufacturers mean so much to you?

I'll agree - "sharpness" IS germane to many photographers in the quest to make a beautiful print. "Many" does NOT mean "All" and I am in the other camp.

You say "aesthetics has nothing to do with it" ... are you talking about what is considered "beautiful"?

I'm sorry I'm not considered "one of the bright ones" in your book,...

Click to expand...

No, I think you are very "bight". I never meant to infer anything else.

If you really have to ask endlessly repeating "But why?" questions, simply because you are unwilling to accept what you're told without proof,..

Click to expand...

I am not seeking "proof"... only somewhat reasonable avenues of investigation. If something fails my reality testing (e.g. Beauty = fine resolution and/ or "sharpness) I usually will not change my opinion.

... then you're looking in the wrong place by asking it on a forum.

Click to expand...

Does it make sense, then, to argue it an a "forum"?

You will never get your answer here to your satisfaction. You can skeptically question optics all the way back to the laws of physics and the origins of the universe if you want.

Click to expand...

Hey, why not. Somewhere along those lines of inquiry, I might find a pearl or two of useful information.

I'd suggest you look in any number of textbooks on the subject to get your answer. I'm not even sure that will help, because it's not primary literature, so you may need to stop by Cambridge, visit the archives in the MIT library, and look up the original journal articles that define our understanding of optics. And then report back to us, because I'm honestly interested in this stuff and wouldn't mind a more robust understanding than I already have.

Click to expand...

Wow!! How impressive ... you obviously have some experience with MIT!! And you assume that I don't? Why (oops! - strike that)... how did you reach that conclusion? See my book recommendation - van Heel & Velzel, What is Light.

"Report back to you?" No, I won't. It would not be worth the effort.

Now, I've been nothing but nice to you in this thread, and have discussed this topic to the best of my understanding out of shared interest. Clearly either your background in optics, your inherent cynicism, or both make you not accept what I write. That's fine, I mean I have my own area of academic expertise that would not be that swayed by a lay-discussion. But you've personalized this to such a degree that I'm really not enjoying it anymore. I hope you get your answer.

Click to expand...

Really? Where have I "personalized" this? - Not to you, anyway. There was another here who was stooping to insults ... but that was not you ... was it?

"You are not ..."? Was it my mission here to provide for your "enjoyment"?

Actually, I don't have any experience with MIT, nor did I assume or suggest (implicitly or explicitly) that you didn't. I don't know anything about you, your history, or that book you mentioned. I ride by MIT on my bike rides, I drive by it on the way to Calumet Photo, and I occasionally take pictures from Memorial Drive in front of the campus. I was suggesting it because you're not so far away from Cambridge, and MIT as far as I know is reasonably widely recognized for its preemenince in various fields of physics and engineering. But I'm taking that for granted, never having been affiliated with MIT myself. You could also stop at the appropriate libraries at Harvard, BU, or Wentworth Polytechnic and they'd probably have information on the subject.

This is getting weirdly heavy.

Diffraction imposes an absolute limit on resolution at a given contrast at any given aperture. Up to the aperture where the lens is diffraction limited, other factors are imposing their limits instead. Ole's early post summed it up perfectly, and no-one with any knowledge of the subject could dispute what he said. The only thing I'd add to Paul's recent post iis that because there is no such thing as a perfect enlarger lens (though scanners can come close), a 10x magnification off 70 lp/mm will probably give you more like 60 lp/mm on the print, not 70 lp/mm. His point about the 11x14 contact print is unanswerable.

Something I've not seen (I may have missed it) is that the practical limit of resolution on the film is often imposed by film location. A few years ago I attended a Zeiss symposium on exactly this subject. You can get 200 lp/mm on the film -- IF you can get the right film in exactly the right place. In the real world, 125 lp/mm is the best you can realistically hope for with a medium-contrast (printed) target, a real 35mm camera, and a sharp film such as Ilford Delta 100. You won't see it all the time because of film location (depth of focus, not depth of field) problems. The most you can hope for reliably with most lenses on most 35mm cameras is 100 lp/mm, though I saw 125 lp/mm more often than not with a 75/2 Summicron on three different bodies (Leica and Voigtlander).

Finally, visual acuity is not cut-and-dried. Not only are there individual variations, but a certain amount depends on the subject matter. I used to believe in the 1-minute-of-arc figure quoted elsewhere (near enough 16 lp/mm) but I have since grown to appreciate Ctein's argument that the finest detail visible as a discontinuity in a straight line (the 'vernier acuity') is actually considerably higher, so my criterion for "pretty damn' sharp" is now 10-20 lp/mm. Under 10 lp/mm, you really can see a diference. Over about 20 lp/mm, you can't see a real difference in a real print, though you might see a difference with a vernier discontinuity at 30+ lp/mm. Somewhere between 10 and 20 lp/mm is, as far as I can see, where most people lose the ability to see the difference.

Cheers,

R.