The Maths of a Fine B&W Print

[Photo Engineer]

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

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

 

[Jed Freudenthal]

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....

Ed:
Let me try to explain this. I hop, I will succeed.
Of course, 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 is sensitive to any change in light across the retina. This change ( or gradient) is a one dimensional phenomena; although one can look at the change in many directions. In other words: our eyes are sensitive to any change in brightness in the world around us or densities on a photographic. print.
Here comes the idea of contrast transfer around the corner. This is of importance how images are transferred through a lens, in the human eye, through the atmosphere, name it. The language to describe the contrast transfer is MTF, and is applied in numerous different areas. This description is a one dimensional description.
I hope, this will explain this. If not, please let me know.

In my comparisons, I keep the magnification factor for the print constant.

Jed

 

[Ed Sukach]

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 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.

I'm not going to hold my breath. Come to think of it ... what could be a more intense oxymoron than "perfect art". Doesn't a player piano repeat notes, nearly perfectly every time? And in this "near" perfection, doesn't the lack of the human element - read "mistakes" - tag the work, and establish the indelible identity of "Player Piano Played"?

A camera - and its lens - are tools ... in the same sense that a hammer is a "tool". A really "good" carpenter - or photographer - will probably use a superior hammer - whatever that means to them; a photographer is apt to do the same... BUT ... terrible carpentry or photography can be created with the FINEST of tools; and utterly beautiful carpentry/ photography CAN be - and often IS - made with - well - the "Holgas" of hammers and cameras.

I have a MINOR interest in MTF (believe "minor" or not), I think as a leftover from my days testing lenses and marveling over the miracles of optics. However, I NEED to know the "MTF' of all my lenses as much as a carpenter NEEDS to know the Rockwell Hardness of his hammers:

NOT much.

 

[Ed Sukach]

... 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.

"We"???

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].

Only "rods"? What happened to the "cones"?

The human eye ...
... I hope, this will explain this. If not, please let me know.

An oversimplification IMHO. I understand what you have written .. but do not take that as aquiesence to the idea that "understanding MTF is VITAL. I don't think it is.

In my comparisons, I keep the magnification factor for the print constant.

Really? Then you made 8" x 10" prints from your 4" x 5" negatives - and 4" x 4" prints from 6cm x 6cm (2X) - or do I have that wrong?
Hmm. Did you use the same enlarging lens for both formats?

 

[gainer]

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

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. 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.

 

[Jed Freudenthal]

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

 

[Alan Johnson]

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.

 

[Jed Freudenthal]

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.

Apparent sharpness is a parameter not really defined. Although some people consider 'high microcontrast' sharp. In MTF language there is no such thing as sharpness. However in one German study they could correlate an optimal spatial frequency of the human eye with the MTF values of a photographic system. [ This spatial frequency is a little above the point where the MTF of the human eye peaks]. 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.

Jed

 

[gainer]

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.

 

[eddym]

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"?

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."
The US Army photography textbooks use 0.003" for 2-1/4 and 0.006" for 4x5.
Linhof uses 0.0038" for 4x5.
My understanding is that most consider 0.005" acceptable for 4x5.
Contact prints (according to my notes from many years ago) have a cc of 0.01".

 

[Roger Hicks]

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 Sukach]

Ed, you didn't get an answer for that question,

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.

...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, ...

Sounds good to me from memory. Thanks for the "chiming".

 

[Ed Sukach]

... 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.

Mr. Freudenthal.

In all honesty I am becoming more and more frustrated by what seems to me a definte pattern of evasion. I've asked a number of quesions about your data and references - and have received few answers.

I disagree, intently, with the idea that the 4 x 5 format is "approximately" the same as the 6cm x 6cm - and your implication that it is only twice the size (another disagreement) - so therefore of no importance. No - these are NOT you words, this is my interpretation of the message you are trying to send.

I firmly believe that there are thousands (if not infinite) characteristics that should be considered in a PURELY technical evaluation of a print. To single out "MTF" of the lens .. system ... human eye - wherever we are - is is really of minimal practical use, about on the same level as measuring Dmax and Dmin ALONE would be.

I will make one more effort at communication here. You speak of a judgement (survey?) of 17,000 "panelists". Having a Statistical Analysis background, that has set of a few of my sensors, that fire when I here inferences like this. Seventeen thousand is a VERY large sample size - usually there is very little gain in confidence after 125 (with distrubitions being "normal" or close to normal). WHO were these 17,000 - HOW was that "panel" formed, and HOW as the data collected? - and by no means least - HOW were the results analyzed? I would appreciate a concrete "reference" to all this work (web site?).

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.

 

[Photo Engineer]

Did you know that higher dmin can decrease the percieved sharpness (MTF) of a print? A softer toe can do the same. Even though the measured MTF can be the same (or was the same before some klutz messed up the dmin.. etc).

I think Ed, Roger, Patrick, we are dealing with someone who has little pracitcal experience but is long on theory. I have forwarded a long (60 page) article to a fellow APUG member by Mike Kriss titled "A Review of the Old and New Methods of Evaluating the Image Structure of Color Films". This is a rather definitive article on two methods of making such measurements on film itself.

His first sentence is "One's impression of a color photograph's quality is dominated by its contrast and color reproduction. Only after a closer look does one determine if the photograph is indeed sharp......" He goes on to say "Only when two photographs are comared side-by-side can one appreciate the importance of the superior image quality".

In the end, he develops an integral that defines the "Eye and Information Capcity" which is the response of the eye and the information on the film. He goes on to say though that there are indications that the response of the eye to "one dimensional variations, i.e., edges".

In the end, his hypothesis is that more than one equation is needed to describe the various types of image. and he adds in his closing remarks that "the ability to use the methods described in this chapter will be strained to some degree by the basic non-linear nature of the photographic process".

This summarizes the nearly 60 pages of calculus and diagrams and concludes that really, no one way can do it all. Lets let the armchair physicist stew over this. There are reams of things unpublished in the EK archives that no one will ever see....

(Permission to quote Mike's article are gratefully acknowledged. Thanks Mike. The article was published in an SPSE book available only to members who were conference attendees.)

PE

 

[gainer]

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".

The circle of confusion is best described by the angle it subtends. The choice of limiting angle then becomes less arbitrary when it deals with things that are to be observed by humans. The minimum angle and the proposed viewing distance then specify the linear diameter of the circle of confusion that is required for critical sharpness, but the linear diameter need never be used in a calculation.

 

[Michel Hardy-Vallée]

12 pages down the road, and the OP still hasn't said thanks for all the confusion. I call shenanigans on him!

 

[Photo Engineer]

Forget him Michael, we are sure doing our best to help Jed.

PE

 

[Jed Freudenthal]

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.

The Swedish study was done at the department of physics, Institute of optical research Royal Institute of Technology, Stockholm.
K. Biedermann and Y. Feng, Lens performance assessment by image quality criteria, SPIE vol. 549, Image quality, an overview (1985) 36-43.

The US study, at the Kodak Research Laboratories,
E.M. Granger, K.N. Cupery, An optical merit function (SQF), which correlateswith subjective image judgements.
Photographic Science and Engineering 16, 3, 1972.221-230.

G.P. Corey, M.J. Clayton, and K.N. Cupery,
Scene dependence of image quality. Society of Photographic Scientists an Engineers, 1983, 9-13.

On the MTF of the human eye are numerous papers. One of them:
R.W. Gubisch, Optical performance of the human eye, Journal Optical Society of America, 57, 1967, 407-415.
And one can find many more revent publications on this subject.

The Zeiss report on MTF measurements and film flatness were published on internet. However, they are certainly published in one of their printed publications

I hope, these publications will give more insight in the subject of 'image quality'. I am not aware of other approaches to this subject.

Jed

 

[Ed Sukach]

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...

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. [/QUOTE]

 

[Jed Freudenthal]

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.

[/QUOTE]


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. ). I also ordered papers from the library of congress in Washington DC. On internet you can locate in what libraries the papers are. More of a problem might be the German language. The German study is actually more studies in one. And the information is 'compact' and complete. For example when 'experienced' panels were used, a blind comparison panel was used as well. It really is a thorough German study. Every information you are looking for, is in it.
However, I recommend to read all the studies ( and their references) as one large report. You will notice that they also report on variables that are not covered by MTF as well.

The Zeiss study has been published around, I would say, 1995/6. As a result of that study, a special apparatus with a microscope has been build to measure film flatness directly. This apparatus is used since around 2000. Therefore, I am referring to the start of the study by Zeiss. As a result, Rollei modified the back of my SLX in their factory, but that is an action in between. The back of the 6008 is completely different from the back of the original SLX.

In the Swedish report is a plot between the critical spatial frequency and the perceived image quality (figure 3) and I quote their english comment : ' From this plot it is evident, that in viewing a picture from a distance of 40 cm, The MTF at 2 c/mm has very strong correlation with perceived image sharpness'. The report shows that the value of the MTF is scene dependent ( a landscape has to be detailed, a portrait not; the MTF of a portrait lens should be low; the MTF for landscapes high). However, all scenes will peak at the 2 c/mm.

In the Swedish report, you will find also a comparison between their study and the study of the Kodak research lab . These studies are in excellent agreement ( The Kodak research group used a range of spatial frequencies, covering most of the MTF of the human eye).

In the German report the standard deviations of the results of the studies with five different panels are given. In the Swedish report standard deviations are given as well.

Jed

 

[Ed Sukach]

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.

Interesting ... I've totalled the number of students, instructors, support personell ... from the University of Munich web site .. and it amounts to 14,890. The only way a panel of 17,000 could be formed is to have introduced others from ... where? Or does this "Within a factor of two" apply? The number of panel members could then be 8,500 to 34,000...? ... but that wouldn't be "significant", would it?

I have to be truthful: I don't believe that a panel of 17,000 EVER existed.

Now ...

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. ).

No problem at all ... IF you are a Member of the Faculty or a Student at U of Minn. or Yale ... I am neither... nor am I a member of SPIE, or the Optical Society of America.
After a brief excursion ... net result: waste of time, I am abandoning the "search." I have things to do ... and continuing here is not one of them.

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.

Good luck in your course of Instruction.

Sayonara! - and

-30-

 

[Roger Hicks]

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.

Dear Ed,

Seconded. I am not ex-Nasa or ex-Kodak or in the same league as several others among Jed's distinguished critics -- but I do know a little about the subject, and increasingly I suspect that Jed knows even less.

Cheers,

R.

 

[pentaxuser]

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.

If (and of course it is an unknown "if") we have succeeded in turning him away on his first and possibly only post to APUG then it is a pity.

It can be so easy to lose sight of the customer, in this case paulcop. If we do then we lose "business".

In the hope that he is still logging on to APUG and still reading this thread, I invite him to tell us how he believes his thread was handled.

I know that I have had good answers to my threads from most of the contributors to this thread and it would be a pity if he doesn't view the potential of APUG to help him in the same light as I do.

We can only wait and see if he responds.

pentaxuser

 

[Joe VanCleave]

Re: Helping the original poster

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 know it's considered extremely bad form to have to quote yourself; too much shouting; not enough listening.

Hopefully, if the original poster has any further questions, he can PM me.

 

[sanking]

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

Hi Pentaxuser,


I was a witness in a case a couple of years ago in which one of my former colleagues was suing two other colleagues for defamation. The issue was whether or not a certain kind of "doctorat" taken from a university in France in the late 60s was the equivalent of an American Ph.D. Very complicated issue because there are several different kinds of doctorats given at French universities, and the requirments now are not the same as they were when the degree in question was issued. And then there is the complication that all Ph.Ds granted in the US are not equal because of the standards at different schools.

The jury deliberated two days without reaching a decision, at which point the judge managed to get the contending parties to reach a settlement. In his remarks to the parties he indicated that the jury was fairly confused (in fact, I suspect they were totally bewildered) by the fine subtleties being advanced to support or or the other position.

I don't know about Paulcop, but my opinion is that his original question was appropriately answered at the beginning of the thread when it was suggested that he "show" examples of his work and try to convince with his own enthusiasm rather than get into specifics like Dmax, apparent sharpness, etc. If he takes the later path, most anything he hangs his hat on is open to extensive debate. This kind of intellectual masturbation is often neither useful nor pleasurable.

Sandy King