Speed Increasing Dev Question

[jmal]

When using a speed increasing dev (like DD-X mentioned recently in another thread), I'm assuming this "underexposes" or underdevelops the negative a given amount, similar to pushing film speed. Am I correct in this assumption? If this is correct, would I then need to further overexpose the film (i.e. adjust film speed by the same amount in the opposite direction) in the camera? Thanks.

Jmal

 

[David A. Goldfarb]

A speed increasing developer like Acufine or Microphen lets you expose the film at a higher speed than the box setting (i.e., it lets you "underexpose" in camera, but you're not really underexposing, because the speed is really higher), but still retain good shadow detail and normal contrast at the reduced exposure.

This differs from what people normally call "pushing" (attempting to increase film speed substantially by extending development time), which usually increases density in the highlights while not really improving shadow detail significantly, and film speed is measured in terms of shadow detail.

 

[jmal]

David,

I think we're on the same page; I was just a little sloppy in my terminology. So, if I shoot Tri X at 200 normally, with a speed increasing developer, I could shoot it at the 400 box speed and get the same exposure (assuming the dev increases speed a full stop)? Yes?

Jmal

 

[David A. Goldfarb]

I wouldn't necessarily compare it to what your other developer is. I find I can get a reliable EI of 800 with TX in Acufine, and 640 with TXP, for instance.

Better just to develop the fim in your speed developer of choice and test it on its own terms.

 

[jmal]

Thanks. I'll start with the suggested times and work from there. I'm always looking for the easy way, but...Thanks.

Jmal

 

[Roger Hicks]

When using a speed increasing dev (like DD-X mentioned recently in another thread), I'm assuming this "underexposes" or underdevelops the negative a given amount, similar to pushing film speed. Am I correct in this assumption? If this is correct, would I then need to further overexpose the film (i.e. adjust film speed by the same amount in the opposite direction) in the camera? Thanks.

Jmal

ISO film speeds are defined by the minimum exposure to give a fixed density at a given contrast. This varies according to the developer: the same 'ISO 400' film, in different developers, might range from ISO 200 (or less) to ISO 650 or slightly more. There is almost no limit to the speed you can use, but one full stop is usually the absolute limit you can gain.

Most (not all) manufacturers use a 'middle of the road' developer such as ID11/D76 for speed determination. Use a speed increasing developer and you will get more genuine speed (and bigger grain); use a finer grain developer and you will get smaller grain, but less speed.

Extra agitation also gives a small but measurable increase in true film speed.

Many people confuse ISO speeds (scientifically determined and replicable) with EIs, or exposure indices, which can vary quite widely according to subject matter, lighting and personal preference.

There's an entire free module on ISO film speeds in the Photo School at www.rogerandfrances.com.

Cheers,

R.

 

[jmal]

Roger,

I guess in a roundabout kind of way I'm trying to figure out where to start with DD-X. After the positive comments in the other post, I decided I wanted to try it. I have been shooting 35mm Tri X (in HC-110 dil B or H) at EI 200 and cutting development a bit based on the light conditions. I arrived at this EI with no particular scientific testing, but rather trial and error. It seems to give a little better result than the box speed. I'm at a point where I've used D76 and HC-110 enough to have a good idea how they work and I'm still intersted in toying with others. I do need to stop at some point and pick something for consistency (though my results have never differed greatly). If I had to choose today, it would be D76, but I want to try the DD-X and see what I think. Anyhow, I have a couple of rolls with some potyentially good shots and I don't want to blow them. At the same time I don't ever shoot things that aren't meaningful to me, so I never have a junk roll to experiment with. I know it's a false economy to gamble with the good rolls rather than spending a few bucks on a test roll, but I feel risky. Also, I've never had any rolls come out unprintable, so I imagine I'll be okay just using Ilford's times. Any other advice for DD-X is appreciated.

Jmal

 

[Roger Hicks]

Any other advice for DD-X is appreciated.

Jmal

Okay: here's a bugger. Ilford often give EI dev times for their devs, so DD-X @ 400 with an ISO 400 film will almost certainly be slightly low in contrast (I've not checked this with them but I do know about the EI trick. Their view is that it avoids confusion.

If I were you I'd give 10 per cent OVER the published Ilford time for DD-X (or split the time between 400 and 800). This should give roughly the ISO contrast/speed point and thus (by definition) the ISO 650+. This is what I do, but I then rate the film at 400-500 with a spot meter, giving myself +1/3 to +2/3 stop, where I prefer the tonality.

Hope this helps. As you say, it's unlikely to be unprintable in any case.


Cheers,

R.

 

[jmal]

Roger,

Thanks for the info. However, as I shot at EI 200 I'm not sure it applies. Ilford gives a time of 6.5 minutes for EI 200. Should I split the difference between 200 and 400? Or, add the same percentage listed above to the 200 time? Thanks.


Jmal

 

[Paul Howell]

I use DDX for Tmax 3200 35mm. I shoot at 1600, duilte 1:5 rather than 1:4 and devleop at 3200 times, gives me good shadow without blocked highlights. I find it diffcult to get true 3200 speed with DDX or Tmax, at least for my equipment. For most 400 speed films I would try 200 at 1:5 at 400 times as well for a starting place. If you have access to a densitomer you can get a very percise EI.

 

[Roger Hicks]

Roger,

Thanks for the info. However, as I shot at EI 200 I'm not sure it applies. Ilford gives a time of 6.5 minutes for EI 200. Should I split the difference between 200 and 400? Or, add the same percentage listed above to the 200 time? Thanks.


Jmal

Dear Jmal,

Well, there's no advantage I can see in using DD-X. You've already over-exposed, reducing sharpness and increasing grain, and DD-X will increase grain again. On the other hand, I suppose it might look good tonally. I'd give it 7 minutes and see how it looks.

Cheers,

R.

 

[Jed Freudenthal]

A speed increasing developer like Acufine or Microphen lets you expose the film at a higher speed than the box setting (i.e., it lets you "underexpose" in camera, but you're not really underexposing, because the speed is really higher), but still retain good shadow detail and normal contrast at the reduced exposure.

This differs from what people normally call "pushing" (attempting to increase film speed substantially by extending development time), which usually increases density in the highlights while not really improving shadow detail significantly, and film speed is measured in terms of shadow detail.

There are several definitions of film speed (ASA, ISA, DIN etc). The film speed can be changed (in a limited way) through the development time.
In the case of a compensating ( or HD) developer one will observe more detail in the shadows, but this is not the result of a film speed increase. A compensating ( or HD developer) has the ability to show the actual light distribution in the deep shadows. Whether you will observe the actual light distribution in the deep shadows depends on the quality of the camera lens too.
The film speed change has a chemical origin; the struture in the deep shadows has a physical origin.

Jed

 

[Roger Hicks]

There are several definitions of film speed (ASA, ISA, DIN etc). The film speed can be changed (in a limited way) through the development time.
In the case of a compensating ( or HD) developer one will observe more detail in the shadows, but this is not the result of a film speed increase. A compensating ( or HD developer) has the ability to show the actual light distribution in the deep shadows. Whether you will observe the actual light distribution in the deep shadows depends on the quality of the camera lens too.
The film speed change has a chemical origin; the struture in the deep shadows has a physical origin.

Jed

Dear Jed,

Not exactly. First, all speeds are now ISO, which is based on the older ASA and DIN standards. These are now about as relevant as GOST, Scheiner, etc. but may be treated interchangeably with the respective ISO arithmetic and logarithmic speeds, e.g. ISO 400/27 is equivalent to ASA 400 or DIN 27.

Second, true film speed cannot be changed by varying time. You can get more density at the speed point (0,10 above fb+f) by increasing development, but only at the expense of increased contrast. This is commonly known as 'pushing'.

Third, true film speed can be affected by developer choice, as noted earlier.

Fourth, a compensating developer does nothing for the shadows, but decreases highlight contrast, allowing a longer brightness range to be represented without dodging or burning, at the expense of compressing the mid-tones.

Fifth, compensating and HD developers are completely different creatures, assuming you mean 'high definition' by HD. HD or acutance developers emphasize microcontrast at light/dark borders, at the expense of some sharpness.

Sixth, shadow detail depends on exposure, and differentiation of shadow detail to some extent on flare. Flare is a function of the lens and camera body -- the latter is often forgotten.

Seventh, I should be much obliged if you could expand upon your statement about chemical and physical changes as I could not quite understand it.

Cheers,

Roger

 

[Soeren]

Dear Jed,

Not exactly. First, all speeds are now ISO, which is based on the older ASA and DIN standards. These are now about as relevant as GOST, Scheiner, etc. but may be treated interchangeably with the respective ISO arithmetic and logarithmic speeds, e.g. ISO 400/27 is equivalent to ASA 400 or DIN 27.

Second, true film speed cannot be changed by varying time. You can get more density at the speed point (0,10 above fb+f) by increasing development, but only at the expense of increased contrast. This is commonly known as 'pushing'.

Third, true film speed can be affected by developer choice, as noted earlier.

Fourth, a compensating developer does nothing for the shadows, but decreases highlight contrast, allowing a longer brightness range to be represented without dodging or burning, at the expense of compressing the mid-tones.

Fifth, compensating and HD developers are completely different creatures, assuming you mean 'high definition' by HD. HD or acutance developers emphasize microcontrast at light/dark borders, at the expense of some sharpness.

Sixth, shadow detail depends on exposure, and differentiation of shadow detail to some extent on flare. Flare is a function of the lens and camera body -- the latter is often forgotten.

Seventh, I should be much obliged if you could expand upon your statement about chemical and physical changes as I could not quite understand it.

Cheers,

Roger

I thought the filmspeed was determined by the minimum amount light that will expose the film (Expose for the shadows)
You say that compensating devs does nothing for shadows but only highlights, how about Diafine? Is it both compensating and speed increasing (though not with all films) as two different qualities?
Can one say that the speed of X film in Y dev depends on a treshold value as in how exposed need the silverhalides to be for the developer to start working on them. Hight treshold (more light) = slow speed and low treshold (less light) = high speed.:confused:

 

[Roger Hicks]

I thought the filmspeed was determined by the minimum amount light that will expose the film (Expose for the shadows)
You say that compensating devs does nothing for shadows but only highlights, how about Diafine? Is it both compensating and speed increasing (though not with all films) as two different qualities?
Can one say that the speed of X film in Y dev depends on a treshold value as in how exposed need the silverhalides to be for the developer to start working on them. Hight treshold (more light) = slow speed and low treshold (less light) = high speed.:confused:

Film speed is determined by the amount of light required to give a certain density (NOT a minimum density) AT A FIXED CONTRAST. And at this fixed contrast, the amount of light required will depend on the developer and (believe it or not) the agitation: more agitation = more toe speed at a given contrast.

Yes, it is possible (I believe) to have a dev that is both compensating and speed increasing, and Diafine lovers claim this for their favourite developer, but I have never done any sensitometric testing of this myself, nor do I know of anything other than anecdotal or distinctly amateurish evidence that it is true -- but I've never looked, so it may well be true.

Thresholds (the minimum amount of light required to create ANY density) are another matter entirely. They were used in some early speed testing systems but were soon dropped as unreliable, hence the DIN standard of 0,10 above fb+f and the later Kodak fractional gradient system which became ASA and is now integrated surprisingly cleverly with the DIN standard in the Delta X criterion.

Cheers,

R.

 

[Jed Freudenthal]

Dear Jed,

Not exactly. First, all speeds are now ISO, which is based on the older ASA and DIN standards. These are now about as relevant as GOST, Scheiner, etc. but may be treated interchangeably with the respective ISO arithmetic and logarithmic speeds, e.g. ISO 400/27 is equivalent to ASA 400 or DIN 27.

Second, true film speed cannot be changed by varying time. You can get more density at the speed point (0,10 above fb+f) by increasing development, but only at the expense of increased contrast. This is commonly known as 'pushing'.

Third, true film speed can be affected by developer choice, as noted earlier.

Fourth, a compensating developer does nothing for the shadows, but decreases highlight contrast, allowing a longer brightness range to be represented without dodging or burning, at the expense of compressing the mid-tones.

Fifth, compensating and HD developers are completely different creatures, assuming you mean 'high definition' by HD. HD or acutance developers emphasize microcontrast at light/dark borders, at the expense of some sharpness.

Sixth, shadow detail depends on exposure, and differentiation of shadow detail to some extent on flare. Flare is a function of the lens and camera body -- the latter is often forgotten.

Seventh, I should be much obliged if you could expand upon your statement about chemical and physical changes as I could not quite understand it.

Cheers,

Roger

Sure, film speed nowadays is almost always ISO. But in pictorial photography, this number has the finction of a reference point. Lightmeters are even calibrated in two different ways ( I got two Rolleis back from Rollei, and they were calibrated differently!).

But now the question on the chemical and the physics side of the problem. I could try to explain this in 'common language', but this is not easy compared to the scientific way.
Therefore the scientific approach first. But please let me know, if that is not clear.

The photographic process is a process of image transfer: through the camera lens, through the development process/ negative, through the enlager optics and finally the print on th paper. Each step is described by a Modulation Transfer Function ( describing the transfer of contrast). In this image transfer process, one can recognize physical and chemical contributions.
When you look at a print in the deep shadows with structure, you should ask what is coming from what. Is this because of the properties of the camera lens, the developer, the film etc. In fact, with a camera lens with a high MTF at the higher spatial frequencies, a compensating or high definition developer, one can observe more than onbe reason that a deep shadow is structured. It requires experimenting to see what influences what.
I hope, this clarifies my statement a bit more.

Jed

 

[Roger Hicks]

Sure, film speed nowadays is almost always ISO. But in pictorial photography, this number has the finction of a reference point. Lightmeters are even calibrated in two different ways ( I got two Rolleis back from Rollei, and they were calibrated differently!).

But now the question on the chemical and the physics side of the problem. I could try to explain this in 'common language', but this is not easy compared to the scientific way.
Therefore the scientific approach first. But please let me know, if that is not clear.

The photographic process is a process of image transfer: through the camera lens, through the development process/ negative, through the enlager optics and finally the print on th paper. Each step is described by a Modulation Transfer Function ( describing the transfer of contrast). In this image transfer process, one can recognize physical and chemical contributions.
When you look at a print in the deep shadows with structure, you should ask what is coming from what. Is this because of the properties of the camera lens, the developer, the film etc. In fact, with a camera lens with a high MTF at the higher spatial frequencies, a compensating or high definition developer, one can observe more than onbe reason that a deep shadow is structured. It requires experimenting to see what influences what.
I hope, this clarifies my statement a bit more.

Jed

Dear Jed,

Thanks for the explanation; I think I now have a better grasp of what you meant. As I said, I do not see that a compensating developer will have any effects on the shadows -- visualize a D/log E curve for both compensating and non-compensating developers and I think you'll agree -- and I am some way from convinced that an HD developer will have any effect on subtle shadow graduations, given that it works only at abrupt light/dark (and of course dark/darker) interfaces. And, as I noted, the MTF must be considered as a system, including camera flare as well as lens flare.

I'd dispute 'calibrated differently', too, suggesting that the two meters (assuming that they are otherwise identical cameras) are calibrated in the same way and to the same standard, but that the variations are a consequence of tolerances in the calibration process. If the cameras are not identical, they cannot be calibrated in exactly the same way, i.e. the process or referents or both of the calibration process must vary. Nit-picking perhaps, but no evidence that there is any film speed standard other than ISO.

I fully take your point about about ISO speeds as 'a reference point', but what else could they be? Many photographers habitually give a little more exposure in the interests of tonality, but this normally remains fairly constant, e.g. if you rate Tri-X at 250 you're likely to be happy with HP5 at 250 too.

Cheers,

Roger

 

[Jed Freudenthal]

Dear Jed,

Not exactly. First, all speeds are now ISO, which is based on the older ASA and DIN standards. These are now about as relevant as GOST, Scheiner, etc. but may be treated interchangeably with the respective ISO arithmetic and logarithmic speeds, e.g. ISO 400/27 is equivalent to ASA 400 or DIN 27.

Second, true film speed cannot be changed by varying time. You can get more density at the speed point (0,10 above fb+f) by increasing development, but only at the expense of increased contrast. This is commonly known as 'pushing'.

Third, true film speed can be affected by developer choice, as noted earlier.

Fourth, a compensating developer does nothing for the shadows, but decreases highlight contrast, allowing a longer brightness range to be represented without dodging or burning, at the expense of compressing the mid-tones.

Fifth, compensating and HD developers are completely different creatures, assuming you mean 'high definition' by HD. HD or acutance developers emphasize microcontrast at light/dark borders, at the expense of some sharpness.

Sixth, shadow detail depends on exposure, and differentiation of shadow detail to some extent on flare. Flare is a function of the lens and camera body -- the latter is often forgotten.

Seventh, I should be much obliged if you could expand upon your statement about chemical and physical changes as I could not quite understand it.

Cheers,

Roger

Dear Roger:
I use High Definition in the way it is used nowadays: high MTF values over the relevant range of spatial frequencies. In the 1960 ties high defintion has been used for high acutance. This gives sometimes confusion. As a matter of fact, you will see the term high definition in many areas (TV and audio, although the term high fedelity is still common)

The flare is an example ehere a reduction of the MTF will show up.

High defintion developers are compensating. A compensating developer is not necessarily High Definition.

Jed

 

[Roger Hicks]

Dear Roger:
I use High Definition in the way it is used nowadays: high MTF values over the relevant range of spatial frequencies. In the 1960 ties high defintion has been used for high acutance. This gives sometimes confusion. As a matter of fact, you will see the term high definition in many areas (TV and audio, although the term high fedelity is still common)

The flare is an example ehere a reduction of the MTF will show up.

High defintion developers are compensating. A compensating developer is not necessarily High Definition.

Jed

Dear Jed,

Fair enough, though I'd suggest that as applied to developers, 'acutance' and 'high definition' are still all but synonymous.

I am not convinced that high definition developers (in any sense of 'high definition') are necessarily compensating, but perhaps you would care to say more about your definition of 'compensating'. Or perhaps you would be kind enough to refer me to the relevant passages in one of the authorities such as Haist or Glafkides.

To me, 'compensating' means 'with reduced developer activity (and therefore film density) in the highlights, normally achieved via dilution and reduced agitation'. Or as Mike Gristwood so graphically put it, "It pushes over the top of the D/log E curve." An acutance developer relies on edge exhaustion, again achieved via dilution and reduced agitation, so I can see the parallel between them, but, for example, some of Geoffrey Crawley's formulations are famed for their acutance at 1+9 but he suggests using them at lower dilutions (1+14 or even 1+19, from memory) for a compensating effect.

Then again, the more I think about it, the harder I find it to understand your definition of 'high definition'.

What are 'the relevant spatial frequencies'? High MTF at low frequencies creates 'sparkle', as research by both Ilford and Zeiss confirms: Ilford quantifies it in lp/mm, Zeiss in frequencies across the image area.

At high frequencies, any developer still offers the age-old trade-off between resolution, sharpness and grain. What is your definition of 'High Definition' if not 'a pretty good balance between resolution, acutance and grain'?

From the way you use all these terms, it sounds as if you know more about the subject than I, but I have not hitherto been so confused by things I was reasonably confident I understood.

Cheers,

R.

 

[Jed Freudenthal]

Dear Jed,

Fair enough, though I'd suggest that as applied to developers, 'acutance' and 'high definition' are still all but synonymous.

I am not convinced that high definition developers (in any sense of 'high definition') are necessarily compensating, but perhaps you would care to say more about your definition of 'compensating'. Or perhaps you would be kind enough to refer me to the relevant passages in one of the authorities such as Haist or Glafkides.

To me, 'compensating' means 'with reduced developer activity (and therefore film density) in the highlights, normally achieved via dilution and reduced agitation'. Or as Mike Gristwood so graphically put it, "It pushes over the top of the D/log E curve." An acutance developer relies on edge exhaustion, again achieved via dilution and reduced agitation, so I can see the parallel between them, but, for example, some of Geoffrey Crawley's formulations are famed for their acutance at 1+9 but he suggests using them at lower dilutions (1+14 or even 1+19, from memory) for a compensating effect.

Then again, the more I think about it, the harder I find it to understand your definition of 'high definition'.

What are 'the relevant spatial frequencies'? High MTF at low frequencies creates 'sparkle', as research by both Ilford and Zeiss confirms: Ilford quantifies it in lp/mm, Zeiss in frequencies across the image area.

At high frequencies, any developer still offers the age-old trade-off between resolution, sharpness and grain. What is your definition of 'High Definition' if not 'a pretty good balance between resolution, acutance and grain'?

From the way you use all these terms, it sounds as if you know more about the subject than I, but I have not hitherto been so confused by things I was reasonably confident I understood.

Cheers,

R.

High definition, as it is defined nowadays, (not just in photography) has an MTF close to 100% over the entire range of relevant spatial frequencies. In practice, the MTF will fall off somewhat at higher spatial frequencies. A developer for scientific applications should always be high defintion ( image distortion as small as possible). For developer/film combinations see publications of Kodak, Agfa/Gevaert and FOMA . Ilford never published their measurements.
In the case of high acutance, the MTF is higher than 100%, in particular at the lower spatial frequencies. It is often obtained, using adjacency effects in the development process.
High Definition and high acutance are two different things in the current terminology. Although, sometimes, high defintion has been used for high acutance, 40 years ago. Grant Haist is using that in his book. This terminology leads to some confusion.
Anyway, I follow the current use of the word. Resolution and sharpness are not in the current vocabulary anymore. Resolution has been replaced by MTF, and sharpness disappeared all together. The MTF description replaced all that.
I have a Kodak publication of 1976, and at that time already, the developer/film characteristic is given through the MTF representation.

We often talk about 'compensating developers'. I rather would talk about a developer with a compensating effect, as has been done in the 1930's ( by Hans Windisch). This means an extension of the contrast range in both directions (highlights and shadows). In the past, the extension in the direction of the highlights was very clear. Nowadays with some modern lenses, with good MTF characteristics, the extension into the shadows is very important. This is not just theory. I made photographs to prove this.


Jed

 

[Roger Hicks]

High definition, as it is defined nowadays, (not just in photography) has an MTF close to 100% over the entire range of relevant spatial frequencies. In practice, the MTF will fall off somewhat at higher spatial frequencies. A developer for scientific applications should always be high defintion ( image distortion as small as possible). For developer/film combinations see publications of Kodak, Agfa/Gevaert and FOMA . Ilford never published their measurements.
In the case of high acutance, the MTF is higher than 100%, in particular at the lower spatial frequencies. It is often obtained, using adjacency effects in the development process.
High Definition and high acutance are two different things in the current terminology. Although, sometimes, high defintion has been used for high acutance, 40 years ago. Grant Haist is using that in his book. This terminology leads to some confusion.
Anyway, I follow the current use of the word. Resolution and sharpness are not in the current vocabulary anymore. Resolution has been replaced by MTF, and sharpness disappeared all together. The MTF description replaced all that.
I have a Kodak publication of 1976, and at that time already, the developer/film characteristic is given through the MTF representation.

We often talk about 'compensating developers'. I rather would talk about a developer with a compensating effect, as has been done in the 1930's ( by Hans Windisch). This means an extension of the contrast range in both directions (highlights and shadows). In the past, the extension in the direction of the highlights was very clear. Nowadays with some modern lenses, with good MTF characteristics, the extension into the shadows is very important. This is not just theory. I made photographs to prove this.


Jed

Dear Jed,

I'm sorry, I'm still having difficulty with this. Like 99.9999 per cent of photographers, I can't measure MTF, so I must take another's word for it. On the other hand I can form very good comparative (not merely subjective) judgements on resolution, acutance and grain. These terms may seem outmoded to you, but they have an enormous advantage over MTF: they are usable in the real world of amateur and indeed professional photography. I therefore suggest that my usage is actually the more useful and generally understood.

There seem to be ever more areas for discussion, such as 'image distortion as small as possible' as applied to developers. There are also distinctions I find odd such as 'compensating developers' and 'developers with a compensating effect," and I really find it very difficult to understand, let alone accept, your assertion about compensating developers having as marked effect in the shadows. This is governed by exposure, speed (which is of course developer related, but nothing to do with compensation) and lens contrast -- or MTF, if you will.

Compensation is not an extension of the contrast range but rather a compression; an increasing differentiation in the toe and the upper part od the curve. In a sense this is a question of terminology: a compensating developer allows the print to accommodate a greater tonal range without dodging or burning, but it reduces the information carrying capacity of the negative.

I think that perhaps it is best to terminate this discussion before we confuse ourselves (and probably others) any more than we have already done. This is not to denigrate your approach merely to suggest that sometimes it is easier and better to stick with a simple-but-imperfect analysis (memorably described as 'lies-to-children' because that's how teaching proceeds) than to seek another model, perhaps (though not necessarily) more accurate, but less applicable. I hope you will not take this as an attack; I shall definitely go away and investigate your usages further. But, as I say above, I question the value of MTF in home-grown comparisons, and I am less than convinced by some of your original assertions.

Cheers,

R.

 

[Jed Freudenthal]

Dear Jed,

I'm sorry, I'm still having difficulty with this. Like 99.9999 per cent of photographers, I can't measure MTF, so I must take another's word for it. On the other hand I can form very good comparative (not merely subjective) judgements on resolution, acutance and grain. These terms may seem outmoded to you, but they have an enormous advantage over MTF: they are usable in the real world of amateur and indeed professional photography. I therefore suggest that my usage is actually the more useful and generally understood.

There seem to be ever more areas for discussion, such as 'image distortion as small as possible' as applied to developers. There are also distinctions I find odd such as 'compensating developers' and 'developers with a compensating effect," and I really find it very difficult to understand, let alone accept, your assertion about compensating developers having as marked effect in the shadows. This is governed by exposure,
speed (which is of course developer related, but nothing to do with compensation) and lens contrast -- or MTF, if you will.

Compensation is not an extension of the contrast range but rather a compression; an increasing differentiation in the toe and the upper part od the curve. In a sense this is a question of terminology: a compensating developer allows the print to accommodate a greater tonal range without dodging or burning, but it reduces the information carrying capacity of the negative.

I think that perhaps it is best to terminate this discussion before we confuse ourselves (and probably others) any more than we have already done. This is not to denigrate your approach merely to suggest that sometimes it is easier and better to stick with a simple-but-imperfect analysis (memorably described as 'lies-to-children' because that's how teaching proceeds) than to seek another model, perhaps (though not necessarily) more accurate, but less applicable. I hope you will not take this as an attack; I shall definitely go away and investigate your usages further. But, as I say above, I question the value of MTF in home-grown comparisons, and I am less than convinced by some of your original assertions.

Cheers,

R.

Dear Roger:

The concept of Modulation Transfer Function (MTF) is very common ( 1,410.000 entries at google). The lens manufacturers are all giving MTF data. Part of the amateur film manufacturers are giving those data. Zeiss is selling densitometers to measure MTF for years, other companies came thereafter. In the seventies there were people at Kodak stressing the fact that image quality has to be expressed via MTF, and they gave the MTF data for their films. C.N. Nelson in chapter 19 on Tone reproduction in the classic work 'The theory of the photographic process 4 th ed (1976) indicates that the application of sensitometry is a macro reproduction and has its limitations. Here, we are talking on micro reproduction. In that case the MTF approach plays an important role.

OK, when you prefer another approach; it is up to you.

I thought, the discussion might be useful because there does not exist an integrated text on the subject for photography based on modern technology. And with 'integrated' I mean the contribution of lenses, films, developers etc. on the quality of the final image.

Jed

 

[Roger Hicks]

Dear Roger:

The concept of Modulation Transfer Function (MTF) is very common ( 1,410.000 entries at google).
Jed

Yes.

I just said that like 99.9999% of photographers, I can't do my own MTF tests, but would have to rely on published figures. As by definition these do not exist for every combination of cameras, lenses and film that I am likely to use, this seems to me a compelling argument for adhering to the older criteria (and testing prcedures).

Cheers,

R.

 

[Jed Freudenthal]

Yes.

I just said that like 99.9999% of photographers, I can't do my own MTF tests, but would have to rely on published figures. As by definition these do not exist for every combination of cameras, lenses and film that I am likely to use, this seems to me a compelling argument for adhering to the older criteria (and testing prcedures).

Cheers,

R.

Dear Roger:
It is not necessary to do your own MTF tests, but it is important to understand the concept of MTF. In this way you can make your own interpretation of say, the quality of a lens. The selection of the lens for your camera can be done in a way, based on facts. Just to give an example.
I realize that many photographers are not familiar with the concept of MTF. Just a few days ago, an APUG photographer came to me with the MTF data of the new Xenar for the Rollei to be sold this year. With these data at hand I could tell what kind of image one can expect from that lens. I hope, photographers can read that kind of data in the future. It is a matter of familiarization. Maybe the subject of a workshop or so.

Jed

 

[Soeren]

Now where were we? Oh yes speedincreasing developers
Cheers
Søren