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acutance vs contrast

"..the situation is complicated bacause of the different steps in the negative-positive process."

And the variables within each step.

Slush in the systems/latitude helps.

Interesting discussion.

Thanks for taking the time to explain as I'm still learning!

Wonderful forum.
 
Jed;

What amuses me is that the average user wants a cheap throwaway camera with a plastic lens and wants instant imaging using diffusion transfer. They don't realize how poor the final image is!

PE
 
Photo Engineer said:
Jed;

What amuses me is that the average user wants a cheap throwaway camera with a plastic lens and wants instant imaging using diffusion transfer. They don't realize how poor the final image is!

PE
Click to expand...

Fortunately, APUG does not stand for average photography user group.

Jed
 
Can someone explain why, if the concept is so fuzzy, and has no predictive value, (other than as mentioned above)... people find it useful at all?

When and how do you in real life (not in a paper or lecture) actually turn to such data rather than your own "personal experience" to pick your film/developer before photographing?

---
I mean, if your own eyes don't tell you then do you actually turn to the data for guidence?
 
Ray, the eye can be deceived easily into confusing contrast and sharpness. Then it is up to the use of actual data rather than viewing to say what is what. OTOH, use what works.

PE
 
Photo Engineer said:
Ray, the eye can be deceived easily into confusing contrast and sharpness. Then it is up to the use of actual data rather than viewing to say what is what. OTOH, use what works.

PE
Click to expand...

This is a perfect description of the problem. At the same time a starting point for a solution.
I try to solve this problem by removing the confusion on contrast and sharpness. This, I think can only be done with photographic images in which this confusion is clarified and then removed.Once that is done, the approach with the actual data ( as mentionerd by PE) will be no problem.

Jed
 
To measure acutance for each film/developer/agitation setup would need a microdensitometer along the lines described in "Controls in Black and White Photography" by R.Henry.One can guess from reading that book maybe one hundred thousand dollars for this.
I daresay the cost of a device for measuring MTF for each film/developer/agitation setup would be similar.
It's difficult to see such data being available in the forseeable future.
 
Jed Freudenthal said:
I am very grateful to Zeiss, that they published in 1947 a method to oversee the complete photographic procedure in terms of image quality.
Click to expand...

Jed - is this Zeiss info published somewhere in the popular press, and in modern times, so that we could look it up?
 

I used micro-densitometers a lot ( for scientific research). Those machines cost easily 100.000 dollars But even with these machines, a lot of information remains hidden.
The image, as you see it with your eyes is what counts. And it doesnot matter that our vision does not show a reality.
But once we want to control the photographic process, we have to work in a reality. And the purpose of the Zeiss paper on image quality is to have control in a realistic world.

Jed
 
Kirk Keyes said:
Jed - is this Zeiss info published somewhere in the popular press, and in modern times, so that we could look it up?
Click to expand...

There are numerous popular introductions on internet

Just type MTF photography or MTF image quality . on google and select your favorite.

Jed
 
Jed Freudenthal said:
There are numerous popular introductions on internet

Just type MTF photography or MTF image quality . on google and select your favorite.

Jed
Click to expand...

Jed, the one site I glanced at did not tip their hat to Zeiss; are you saying (in a very roundabout way) that Zeiss scientists were behind the MTF analytical method?

Ray
 
Ray Rogers said:
Jed, the one site I glanced at did not tip their hat to Zeiss; are you saying (in a very roundabout way) that Zeiss scientists were behind the MTF analytical method?

Ray
Click to expand...

There are numerous papers on the subject. They do not necessarily refer to the oringial paper of 1947.

Jed
 
Jed:
How about quoting or pointing to a seminal one. I don't understand why are we playing footsy and please just point to something you are referring to. It's bad form to broadly say "everybody knows" if you're really are trying to help and illustrate something to somebody, this is why we are here, to help people, right? Please point to something specific and something that we can repeat ourselves, otherwise we are going to have this conversations for ever and ever. Hopefully I don't sound too rude.
Steven
 

I am not JED, but I don't think you are being too rude.
Sometimes this sort of thing happens.

I thought JED might be thinking of Selwyn's work which was done around that time, but I haven't pin pointed what ever paper he has in mind; and for some reason at this point I am too stubborn to simply ask!

Not having the time to footsy, I think I will just encourage JED to consider printing up small pictures that describe what he thinks is helpful to teach the subject... we can pass them round so we can all see the pictures first hand; A verbal description can be sent along or just put up in the articles section for anyone to read, with a link to this thread and perhaps with some suitable but suboptimal pictures....

It's just an idea though....
 


Apparently, it is no good to refer to the original paper. I am a physicist, so donnot tell people that the theory of relativity came from Einstein. Many other people wrote on the subject later on. But connecting it to Einstein is some kind of honor.

But now on the educational part: let me start to quote PE: Ray, the eye can be deceived easily into confusing contrast and sharpness. Then it is up to the use of actual data rather than viewing to say what is what. OTOH, use what works.

The objectve is to remove the deception ( the confusion on contrast and sharpness). I would like to do this by showing appropriate actual photos. If that succeeds, the MTF approach is easy. We (in APUG) are in the process testing this assumption, and when we think we have an appropriate approach, we will come up with the result. But, because, we are in the testing procedure right now, you should have a little patience.
But publishing suboptimal photos will, I think, not work. My idea is to have some kind of postcard exchange to get real images as an illustration of a text.

Jed
 
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We?


JED;
I have patience!

Postcards are fine, but a set of small photographs sent out by you to a list of participants is what I suggested;
the suboptimal digital images on apug was just for the sake of people with medium to low interest levels.

I am sure something nice can be devised... there are many examples, the color "ring-a-round" being one and the ordinary "bracket" being another.

I have even heard there is a lens (camera?) that claims to give you an "MTF bracket" but it sounds too good to be true... perhaps you know of this lens?

Best of luck with your tests....
 
Ray Rogers said:
JED;
I have patience!

I have even heard there is a lens (camera?) that claims to give you an "MTF bracket" but it sounds too good to be true... perhaps you know of this lens?

Best of luck with your tests....
Click to expand...

I do not know what you mean with MTF bracket.
When I have an specific application in mind ( e.g.landscape), I select, the camera, lens, film, developer etc. on the basis of MTF. I am doing that now for say 20 years. During that period of time, a lot of experience builds up. In particular on the behaviour of image quality due to micro-contrast (grain level).
As a result, I am using a different film in Italy than in The Netherlands or Cornwall (UK) etc. Just because the differences in light.

Do not expect to make these subtle selections on the basis of MTF, however MTF can give guidance how to modify the conditions in development etc.
And MTF is extremely helpful in making initial selections.

Once you start using and UNDERSTANDING MTF, it is a start, it is not a finish. You will probably never reach the finish.

Jed
 
Ray Rogers said:
JED;
I have patience!

I am sure something nice can be devised... there are many examples, the color "ring-a-round" being one and the ordinary "bracket" being another.
..
Click to expand...

Apparently, there are already examples. Do you know about the results of ring-arounds? That is kind of similar situation.

Jed
 
Jed,

Are you saying you select the film and developer on the basis of MTF data?
For film on the internet is only a minimal amount of MTF data from Kodak only,probably for D-76 developer.
For developers is only the small amont of data in the book by R.Henry.
Can you say where you get your MTF data for film and for developer? It does not seem to be generally available.
 

A lot of questions. First of all: there are MTF data, and there is an understanding of MTF. Therefore, part is the result of actual data, but much comes from the understanding the subject.

Kodak is not the only firm to supply actual data. I know Agfa and Foma have them too. I got them from internet. But in many cases, I can obtain the information, just by looking at photographs made by these materials. But that requires experience. And as I said already, the finishing touch needs testing, testing and testing.

For developers, you need understanding of MTF. If you are interested in landscape and details are important, a high defition developer is apprpriate to take advantage of detailed information. I have published such developers on the APUG site, as HD developers But if you are taking reportage photos, the forms are possibly more important. Then take a developer that do not show much detail, but show the forms. A medium format or 35 mm film in D 76 or Xtol might be more apropriate
This is just an example. The most important thing is, that you understand MTF. With that understanding, you can structure your photographic process.

Jed
.
 
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