Jed;
I am also a scientist and have had both types of explanation. In the end, the scientific explanation falls in the face of art, or what people want. What people want and prefer defies quantization.
PE
I fully agree with you. But why not give it a try. I checked it lately. I explained MTF to non-scientific people. And, within 10 minutes they understood it. Of course, practice is required to get it in a grip. But for me, this experience was a signal that it is possible to get the idea across.
Jed
A "Factor of two" is still describable as "approximate"??
Unfortunately I don't view a photograph as one dimensional (the length of a single line) ... I see an entire area.
Possibly you might help here .. I was about to look this up, but I am pressed for time at the moment: What is the diameter of the "circle of confusion" used in the design of a lens intended for use with the 6 x 6 cm format; and what is it when designed for 4" x 5"?
BTW - What were the dimensions of the finished prints used in you comparisons?
Also .. Try the MTF charts for the Hasselblad - Zeiss Sonnar CF f/4 150mm for its MTF....
I agree with both you and gainer. When anyone comes up with a viable - even remotely viable - mathematical model for Homo Sapiens, we might stand a chance - but then, a program could be written to produce "flawless" art.Jed;
I am also a scientist and have had both types of explanation. In the end, the scientific explanation falls in the face of art, or what people want. What people want and prefer defies quantization.
PE
... when we look at an image, we look at a two dimensional representation. However, when we are talking about properties like image quality, we have one dimensional properties in mind.
And this is true for a camera as well as for the human eye [the film is just replaced by a set of light sensitive rods in the human retna].
The human eye ...
... I hope, this will explain this. If not, please let me know.
In my comparisons, I keep the magnification factor for the print constant.
This is actually Patrick Anthony Francis Gainer, the alter ego of Gadget Gainer. He made me post this so he wouldn't have to break his promise to say no more.My final word, I promise.
Gadget:
Although I am a physicist, I try to clarify the point in non-scientific language. In the past, I was also sceptical using MTF. But, it might have been around 1980 that somebody told me, Rodenstock made its lenses for 4x5" just meet the quality of the human eye. And Rodenstock, Linhof and the German MTF research group were all in Munchen Germany,
In other words: it is not necessary to make 'better' lenses, because the human eye is unable to see it. I found this intriguing, and I checked it. It was true. After that I made many comparisons between negative sizes, lenses, films etc. And, after a while you get a feeling what the MTF language has to tell. But, it applies to image (print) quality only as judged by humans (subjective). And there is much left in ther artistic domain. Don't worry, MTF is just to control a technical part of the photographic process.
You were mentioning the non-linear parts of film and paper. The MTF applies in these areas too. But, there is much more going on. Kodak tried once to understand and control that. They did not succeed, at least not with simple and practical procedures.
Jed
MTF is not a control. It is an observation gone wild. It means only bits per second or bits per mm. It only means those things when it is used to analyze a linear system. We at NASA tried to use these linear servomotor models to analyze performance of human pilots. It did not work well. There was always a fairly large "remnant". If you want to call it random error, you are doing the pilot a disservice. The pilot had good reasons in actual life to let the "error" be as large as could be safely tolerated in his eyes. You cannot predict every jab and quiver of a pilot's responses by using a linear model. I do not know the status of these modeling efforts in the 25 years since I retired. The object of being able to model the pilot was to be able to design proper display and control systems without the dangers of flight testing. I'd be willing to bet we still employ test pilots and that they have the final say.
Surely you can apply MTF calculations to any set of measured values of input and output, but unless the system that produced the values is linear, the MTF has no reliability. We do well judging most lenses by MTF, but not all. Some which have poorer performance are prized over objectively better ones for what has been described as bokeh. As far as the information content of a photo is concerned, it is as has been said before only a string of bits with a certain aurocorrelation function which could be possessed by a particular distribution of random noise.
Gadget said for me to say hello.
This is actually Patrick Anthony Francis Gainer, the alter ego of Gadget Gainer. He made me post this so he wouldn't have to break his promise to say no more.
MTF is not a control. It is an observation gone wild.
Surely you can apply MTF calculations to any set of measured values of input and output, but unless the system that produced the values is linear, the MTF has no reliability. We do well judging most lenses by MTF, but not all. Some which have poorer performance are prized over objectively better ones for what has been described as bokeh. As far as the information content of a photo is concerned, it is as has been said before only a string of bits with a certain aurocorrelation function which could be possessed by a particular distribution of random noise.
Gadget said for me to say hello.
Hello Patrick Anthony Francis or Gadget.
MTF is used as a control method. I will give an example: The MTF of the print should be the product of the MTF's of the diffent parts ( lens, negative, enlarger). It is often found that the MTF of the print is less than the product of the MTF's of the photographic sequence. The reason is a technical problem in the photographic sequence, like vibrations in the lens during exposure, vibration in the enlarger, poor alignment. The next step is to find and remove the problem. A practical application.
Another example: Zeiss found a technical problem in motordriven medium format cameras through the measurement of MTF. Eventually they found that the MTF of the negative was too low. The reason was that the motordriven film was not lying in a flat plane ( in particular with 220 film). The manufacturers( e.g. Rollei) had to redesign the back of these camera. I call this very practical applications. MTF has therefore a control function. Removing technical problems from the photographic sequence is important for anyone, because these tecnical problems in your equipment will degrade the quality of ALL your prints. Photography is a combination of art and technique. The APUG site is full with questions on technical problems.
Jed
On the topic of the use of 50%MTF,a search for "50% mtf film digital" shows that a few authors have used this to compare color film and DSLRs.There is the problem of trying to represnt both resolution (higher frequencies) and apparent sharpness (lower frequencies?) by one number and 50%MTF lppm appears to be a compromise,but it means there is no strict mathematical theory with the comparison.
I did not see any comparison for B/W film,speculatively it might be said that a similar comparison could be made by reading the 50%MTF off MTF graphs for B/W film but nobody seems to have tested this.Perhaps such a comparison would only be of intrest to the experimenter at present.
Hello Patrick Anthony Francis or Gadget.
MTF is used as a control method. I will give an example: The MTF of the print should be the product of the MTF's of the diffent parts ( lens, negative, enlarger). It is often found that the MTF of the print is less than the product of the MTF's of the photographic sequence. The reason is a technical problem in the photographic sequence, like vibrations in the lens during exposure, vibration in the enlarger, poor alignment. The next step is to find and remove the problem. A practical application.
Another example: Zeiss found a technical problem in motordriven medium format cameras through the measurement of MTF. Eventually they found that the MTF of the negative was too low. The reason was that the motordriven film was not lying in a flat plane ( in particular with 220 film). The manufacturers( e.g. Rollei) had to redesign the back of these camera. I call this very practical applications. MTF has therefore a control function. Removing technical problems from the photographic sequence is important for anyone, because these tecnical problems in your equipment will degrade the quality of ALL your prints. Photography is a combination of art and technique. The APUG site is full with questions on technical problems.
Jed
Your definition of control is different from most. The MTF is no more a control than is a pilot's verbal report of a control problem. One test pilot came right back after takeoff looking a little white in the face. The mechanics had reversed the controls. What should have been up elevator was down. He learned very rapidly and was able to land before he forgot. You cannot include MTF in a control loop. You must do a lot of controlling before you can even compute the MTF.
Ed, you didn't get an answer for that question, so I'll chime in. There is not an officially accepted diameter of the circle of confusion, as far as I know. Different manufacturers sometimes use different criteria; Rollei, for example, gives 0.0033" for 2-1/4 film "for general use," but 0.0022" "for critical use." The former naturally gives a different hfd than the latter, and thus different depths of field. The "critical use" would be greater enlargement, though I don't know how much enlargement is considered "critical."Possibly you might help here .. I was about to look this up, but I am pressed for time at the moment: What is the diameter of the "circle of confusion" used in the design of a lens intended for use with the 6 x 6 cm format; and what is it when designed for 4" x 5"?
Another example: Zeiss found a technical problem in motordriven medium format cameras through the measurement of MTF. Eventually they found that the MTF of the negative was too low. The reason was that the motordriven film was not lying in a flat plane ( in particular with 220 film). The manufacturers( e.g. Rollei) had to redesign the back of these camera.
Jed
Dear Jed,
Sorry, this is complete bollocks. You do not discover technical problems through the measurement of MTF. You discover them because the pictures are not sharp (or have some other visible fault). If the fault is not visible, you don't care. If it is visible, THEN you start looking for why. Poor film positioning and lack of film flatness is an immediate and obvious candidate in this case, so they designed a range of non-contact measurements of film position.
How do I know this? Because some years ago, as a guest of Zeiss, I attended a Zeiss presentation (in Oberkochen) on film flatness. There was a great deal about how film behaves, how it is located, etc., and very little about MTF. You are becoming monomaniacal about one important but far from paramount parameter.
Cheers,
R.
Ed, you didn't get an answer for that question,
...so I'll chime in. There is not an officially accepted diameter of the circle of confusion, as far as I know. Different manufacturers sometimes use different criteria; Rollei, for example, ...
... This study was set up with perceived sharpness as the parameter to be judged by a panel of 17.000 persons. In another study the image quality of the photographic print was the parameter to be judged by a panel, without defining 'image quality'. Apparently most people have the same idea what good image quality is.
Yes, I know. Mr. Freudenthal has been elusive about that, and a few other statements he has made. I'll address that directly with him.
The "circle of confusion" - closely related to the "resolution" description used in telescopes, is one of the criteria used in lens design. Lenses for large format usually are designed with larger "circles of confusion' ~ resovling power, simply because less resolution is needed. C o C diameters ARE arbitrarily chosen - rationalized from experience and practical use.
Sounds good to me from memory. Thanks for the "chiming".
Mr. Freudenthal.
You go on - citing "another study". What was that "study" - and HOW ... etc. (same questions as above) -and WHAT methods were used in the comparison of the two studies?
Hopefully - I'll await a direct answer.
Ed:
The references are:
The German and most extensive study done at the technical university Munchen is:
K. Biedermann, Ermittlung des Zusammenhanges zwischen der subjective Gute und den physikalische Eigenschaften des photographische Bildes. Thesis, also published in Photographische Korrespondenz 103 Bd, nr 3, 1967, p. 5-48. The title translated: Determination of the relation between the subjective image quality and the physical properties of the photoigraphic image image...
[/QUOTE]Interesting... Thank you for your reply.
However - Where did this Seventeen Thousand (17,000) member panel evaluation take place? - and what were the parameters of that particular "testing"? Who WERE these panel members?
Did the number of all of those responding at all these various locations add up to 17,000?
Did all of these studies address the same question, and were the parameters entirely - or closely - the same?
Was there an ABSOLUTE agreement that "sharpness" was the (single? - or ...?) deciding factor in determining "best"? - Or did some fraction disagree?
Where, other than physically traveling over most of this green Earth, can I obtain access to all these studies? I'll try Google, etc., but you should remember that I actually have a life, beyond this discussion.
The German study was in Munchen (Bayern) Germany ( The same place where Linhof and Rodenstock are located). The panel were students and staff of the technical university in Munchen. Munchen=Munich in english.
I think, it is no problem to get the articles via the university library ( at least that is my experience in US university libraries ( Yale and the University of Minnesota e.g. ).
Please - one last request ... Do NOT automatically assume that everyone who disagrees with your line of thought does so ONLY because they "don't understand". Some of us actually DO understand what you are saying, and disagree for a wide range of other factors ... and I am one of them.
Paul, since your target audience seems to be people fundamentally unfamiliar with the techniques of silver gelatin photography, and your stated goal is their understanding of the qualitative tonal aspects of B&W prints, that should in itself guide the creation of your presentation.
And, as stated earlier, don't focus on just one measurable artifact, like DMAX - which is a bad choice, anyways, if your goal is to espouse the unique qualities to a B&W print.
Perhaps you should focus your talk on the basic techniques that photographers use to capture such a rich tonal scale; a dip of the toe into the ocean of information about the various 'Systems' used to capture a given scene's bightness range onto the film and paper media (Zone & BTZS are two such popular systems). Again, you don't need to 'baffle them with BS' and spout forth sensitometry data; just impress them with the wide range of tools and techniques available to photographers working in silver gelatin media.
You could also talk to them in general terms about various film development techniques and their effects on the distribution of silver grains in the resulting fixed emulsion, and how this can affect subtle but important changes to the resulting prints. Impress upon them that our 'optical image sensor' is 3-dimensional, and can be altered at the microscopic level by customizing our 'work-flow' (i.e. the film development process).
You could also talk a bit about the merits of contact printing verses projection enlargement, and the differences between cold light and condensor optics on the resulting print, and the necessary changes required in one's film developing regimen if one were to change enlarger optics or printing technique.
And then there are the wonderful effects of staining developers on controlling print contrast.
Etc, etc, etc.
In summary, impress upon them that the fundamental differences between the worlds of electronic and chemical photography is that electronic photography works much more in the area of the manipulation of abstract 'data', whereas chemical photography operates entirely in the realm of physical processes; as such, B&W silver gelatin photographers are by nature much more attuned to the subtle physical nuances of the materials at their disposal, and therefore more sensitive to disruptions and unexpected changes in their quality, working methods and availability.
I follow most threads here at APUG and I can think of few, if any, where in 13 pages the originator has failed to even acknowledge once the contributions others have made.
As he was a newcomer and this was his first post, maybe we just need to ask ourselves if we answered it in a way which was meaningful to him.
pentaxuser
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