Kodak grey card usage

[markbarendt]

Please explain the concept of 'the speed point'

The simplest way to think of this is that the speed point of a film is the lower limit of exposure.

On the film curve it's down at the bottom on the "toe". This is rightly where the expression "expose for the shadows" comes from, the real numeric values are the numbers on the X axis of the H&D curve. It is the one point that exposure actually gets to define.

The box speed of a film is based on this speed point.

The rest of the points on the films curve are defined by both exposure and development/processing. Hence the rest of the saying "develop for the highlights". Development defines what happens on the Y axis of the H&D curve.

 

[wiltw]

18% is the visual "middle point" of human vision, and corresponds to 128/256 (or 127/255 if we have a representation with the zero) in the digital world.
The scale from 0 to 255 used in the digital world is a "perceptual" one.

The assumption by wiltw that by taking a picture of a grey card he should obtain a colour expressed in RGB as 128, 128, 128 looks to me quite correct. In a slide film 100 ISO he should obtain a density of -1..

My point of view is well expressed by you! If all scale tone charts have something appearing to be 18% reflectivity is 'in the middle' between the extremes of perceptual black and perceptual white, when I 'properly expose' a shot so as to capture everything in the scene 'at their inherent tonality', when that shot is reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white.

Speaking from sensitometry, film might be very different from digital, but the identical principle still applies...when that shot -- 'properly exposed to capture everything in the scene 'at their inherent tonality' -- is reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white.

How I arrive at the 'proper exposure' might match exactly an incident meter reading (or not) or might match exactly a reflected light reading of 18% or 12.5% or 9% (depending upon who you choose to believe), and or it might take moving the reflective target to some very specific yet not always easily replicated angle, and still might require 'creative interpretation' nevertheless, but when that shot -- 'properly exposed to capture everything in the scene 'at their inherent tonality' -- ' is reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white.

And even when I employ some exposure offset to better take advantage of the sensitometric limitations of my capture medium -- ETTR, in the case of digital, or Zone System exposure in the case of film -- when that shot -- 'improperly exposed to NOT capture everything in the scene 'AT their inherent tonality' -- ' is reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white.

If I shoot textiles or fashions for a client, they expect faithful reproduction of their products --'properly exposed to DEPICT the fashion/textile in the scene 'at their inherent tonality' -- ' and reproduced on the printed offset print page, on the photographic print, or on the transparency, THEY expect to see that 'middle tone' in the middle between the extremes of black and white.

The root priciple is 'faithful reproduction' and very likely I must employ different methods to achieve 'faithful reproduction' depending upon my media selection, but my goal is always reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white when I am trying to achieve 'faithful reproduction'

 

[markbarendt]

My point of view is well expressed by you! If all scale tone charts have something appearing to be 18% reflectivity is 'in the middle' between the extremes of perceptual black and perceptual white, when I 'properly expose' a shot so as to capture everything in the scene 'at their inherent tonality', when that shot is reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white.

Speaking from sensitometry, film might be very different from digital, but the identical principle still applies...when that shot -- 'properly exposed to capture everything in the scene 'at their inherent tonality' -- is reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white.

How I arrive at the 'proper exposure' might match exactly an incident meter reading (or not) or might match exactly a reflected light reading of 18% or 12.5% or 9% (depending upon who you choose to believe), and or it might take moving the reflective target to some very specific yet not always easily replicated angle, and still might require 'creative interpretation' nevertheless, but when that shot -- 'properly exposed to capture everything in the scene 'at their inherent tonality' -- ' is reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white.

And if I employ some exposure offset to better take advantage of the sensitometric limitations of my capture medium -- ETTR, in the case of digital, or Zone System exposure in the case of film -- when that shot -- 'properly exposed to capture everything in the scene 'at their inherent tonality' -- ' is reproduced on the printed offset print page, on the photographic print, or on the transparency, I expect to see that 'middle tone' in the middle between the extremes of black and white.

If I shoot textiles or fashions for a client, they expect faithful reproduction of their products --'properly exposed to DEPICT the fashion/textile in the scene 'at their inherent tonality' -- ' and reproduced on the printed offset print page, on the photographic print, or on the transparency, THEY expect to see that 'middle tone' in the middle between the extremes of black and white.

When going straight to positive you can only define one point, the rest fall as they may, if you get middle gray right the rest of the tones will vary more and more from normal towards the ends of the curve.

 

[wiltw]

The simplest way to think of this is that the speed point of a film is the lower limit of exposure.

On the film curve it's down at the bottom on the "toe". This is rightly where the expression "expose for the shadows" comes from, the real numeric values are the numbers on the X axis of the H&D curve. It is the one point that exposure actually gets to define.

The box speed of a film is based on this speed point.

The rest of the points on the films curve are defined by both exposure and development/processing. Hence the rest of the saying "develop for the highlights". Development defines what happens on the Y axis of the H&D curve.

Thank you for the clarification about what is meant by the term. Nevertheless, when I am shooting for 'faithful reproduction' I am wanting the inherent tonality of the objects in the photograph to fall AT their inherent tonality, and that might entail some mods to lighting during capture or film/print making to adjust suitabily to achieve that goal, and the resultant middle grey is still between my extremes of perceptual black and perceptual white. I might be actually limited in where my white point and black point fall, relative to reality, but inherent contrast is still the goal so that white is white and black is black, and near-white is not actually white nor very dark grey seen as black, in addition to middle grey being somewhere very close to the middle, when I am striving for 'faithful reproduction'

When going straight to positive you can only define one point, the rest fall as they may, if you get middle gray right the rest of the tones will vary more and more from normal towards the ends of the curve.

When shooting textiles or fashions, that is the purpose of closely controlling the lighting of the items to be photographed at time of shooting, and ensuring that the offset printed page is capable of reproducing what is captured on the slide.

 

[markbarendt]

Thank you for the clarification about what is meant by the term. Nevertheless, when I am shooting for 'faithful reproduction' I am wanting the inherent tonality of the objects in the photograph to fall AT their inherent tonality, and that might entail some mods to lighting during capture or film/print making to adjust suitabily to achieve that goal, and the resultant middle grey is still between my extremes of perceptual black and perceptual white. I might be actually limited in where my white point and black point fall, relative to reality, but inherent contrast is still the goal so that white is white and black is black and near-white is not actually white, nor very dark grey seen as black, in addition to middle grey being somewhere very close to the middle, when I am striving for 'faithful reproduction'

There's nothing wrong with your goals for your prints wiltw, the disconnect is that camera exposure doesn't, except for slides, define where the tones fall when printed. "Mods" as you put it are inherently required to do what you want.

The gray card is a good tool for helping you get what you want, it's an excellent reference point, forcing it to the middle point though is a choice not a law of physics.

 

[Stephen Benskin]

Actually, speed point is where the film speed is measured. It's not necessarily where the shadow exposure should fall in B&W negative film or where the mid-tone exposure should fall with reversal film.

Technically, I don't think there can be an inherent tonality. A perfect 1:1 match between the subject and the reproduction is not only impractical, but would not yield a satisfactory image. This is based on many psychophysical studies and is part of subjective tone reproduction theory.

 

[Bill Burk]

Now to prints.

Munsell gray 18% makes a great visual middle gray for humans visually judged by millions... So despite lack of evidence, I accept the idea that Kodak Gray Card was selected to be 18% to match Munsell middle gray.

But photographic negative and print, based on their characteristics, cannot give you the other Munsell grays step for step... given changes of exposure stop for stop... even if you develop normal (or to standards) and print on Grade 2. The print is just going to become whatever it will be and we have to accept where the tones fall or make adjustments in the printing session.

It must have driven Ansel Adams crazy to find that every time he metered for Zone V using recommended meter settings the print came out darker. May also corroborate that most Zone System users find their EI is half rated speed... I assume he wanted Zone V to be 18% in the print.

In my Zone Ruler for Normal development, the normal ISO metered point corresponds about to Zone IV and is printed to 7% while Zone V is near 14%.

Let's take another step... Suppose I exposed the negative by standards instead of by Zone System.

I would still want the metered point to be near 14% in the print. So I would get a thinner negative and I would have a shorter enlarger exposure time, and both prints would look about the same.

 

[DREW WILEY]

My remark about Munsell was simply challenging if it ever had anything to do with light metering and film. Why would it? Maybe somebody does know some vague historical connection; but it would seem photographic standards would have evolved completely independently of that, and that the
attempted explanation of gray cards and so forth using it is largely irrelevant. I did a lot of color consultant work at one time, and even back then
the Munsell system was regarded as more a pain the butt than practical. I never heard of it in a photographic context, though maybe somebody made
colored studio background paper or something like that with the system vaguely in mind. It was useless for color matching anyway because printing
ink samples rarely equated well to anything but printing ink.

 

[Stephen Benskin]

Now to prints.

Munsell gray 18% makes a great visual middle gray for humans visually judged by millions... So despite lack of evidence, I accept the idea that Kodak Gray Card was selected to be 18% to match Munsell middle gray.

But photographic negative and print, based on their characteristics, cannot give you the other Munsell grays step for step... given changes of exposure stop for stop... even if you develop normal (or to standards) and print on Grade 2. The print is just going to become whatever it will be and we have to accept where the tones fall or make adjustments in the printing session.

It must have driven Ansel Adams crazy to find that every time he metered for Zone V using recommended meter settings the print came out darker. May also corroborate that most Zone System users find their EI is half rated speed... I assume he wanted Zone V to be 18% in the print.

In my Zone Ruler for Normal development, the normal ISO metered point corresponds about to Zone IV and is printed to 7% while Zone V is near 14%.

Let's take another step... Suppose I exposed the negative by standards instead of by Zone System.

I would still want the metered point to be near 14% in the print. So I would get a thinner negative and I would have a shorter enlarger exposure time, and both prints would look about the same.

Adams and ZS was in the pre-1960 speed standards era where film speeds were 2/3 to 1 stop slower, so your I don't think your supposition applies.

Bill, with your tests, there's the issue of the conditions of the test. Are you exposing a target with a single tone? How are you printing the negatives? What are you basing the print exposure on?

 

[BrianShaw]

My remark about Munsell was simply challenging if it ever had anything to do with light metering and film. Why would it? Maybe somebody does know some vague historical connection; but it would seem photographic standards would have evolved completely independently of that, and that the
attempted explanation of gray cards and so forth using it is largely irrelevant. I did a lot of color consultant work at one time, and even back then
the Munsell system was regarded as more a pain the butt than practical. I never heard of it in a photographic context, though maybe somebody made
colored studio background paper or something like that with the system vaguely in mind. It was useless for color matching anyway because printing
ink samples rarely equated well to anything but printing ink.

That's my understanding as well. It was a landmark work not because it was the first or best color theory, but because it was the first that was both comprehensive and based on psychophysics data. Well, maybe at the time it was the best, but ...

 

[Bill Burk]

Adams and ZS was in the pre-1960 speed standards era where film speeds were 2/3 to 1 stop slower, so your I don't think your supposition applies.

Bill, with your tests, there's the issue of the conditions of the test. Are you exposing a target with a single tone? How are you printing the negatives? What are you basing the print exposure on?

I agree now post-1960 the difference in where the meter aims to place exposure is 2/3 to 1 stop lower than pre-1960. That explains the one Zone difference on my Zone Ruler because I printed as if for Zone System placement which would be 2/3 to 1 stop more exposure on the negative.

My negative is a sensitometric test exposed with EG&G, negative found to have been developed to 0.57 CI. Negative masked to reduce flare reasonably at the enlarger. Printed at my usual height for making an 11x14 print from 4x5 negative on my usual paper. From the resulting prints and graphs that I drew from densitometer readings of the negative and print, I selected which step wedge print chips would represent the camera exposure at the different Zones including 0.4 flare. Flare impacts which chips I chose to represent the lower few Zones.

 

[wiltw]

My remark about Munsell was simply challenging if it ever had anything to do with light metering and film. Why would it?.

Somewhat in line with your question, I have been trying to make the point about 18% grey's use as a visual reference tone on final product, but NOT necessarily as any standardized way to meter for exposure. And as my earlier posts of a grey card at an angle exhibit, the card's apparent brightness does change with angle so it use as a 'standard' is really a 'variable' and not a 'constant' because of the variability. In the Munsell chart, that middle tone was between the extremes of black and white, regardless of the application, and it happened to be darn close to 18% grey (ignoring the reflectivity variable).

 

[DREW WILEY]

Everything in black and white work might be relative, and the so-called Zone System is really just a shorthand method for pigeonholing distinct exposure issues, with exactly zero fixed points of reference other than how the end user himself defines them. I know, I know....Some people like to make a quantifiable religion out of the Zone System and sit cross-legged in the Himalayan foothills on a bamboo mat contemplating how the universe was originally created in eight discrete zones. I'm not one of those people. But color photography, especially chrome exposure, does require some pretty rigid standards due to the linkage of color saturation to specific levels of exposure, not to mention the limited latitude of such films. And that
seems to be the defining characteristic of how certain meters are calculated. The middle of the scale truly means something. I've worked a lot with
both Pentax digital spotmeters, and the IRE scale is there for a reason. You can easily maneuver between color still photography, color cine, and
black and white Zone theory. But anytime I check something, it's with a high quality reference like the MacBeath Color Chart gray scale, not some
generic gray card.

 

[markbarendt]

Actually, speed point is where the film speed is measured. It's not necessarily where the shadow exposure should fall in B&W negative film or where the mid-tone exposure should fall with reversal film.

Technically, I don't think there can be an inherent tonality. A perfect 1:1 match between the subject and the reproduction is not only impractical, but would not yield a satisfactory image. This is based on many psychophysical studies and is part of subjective tone reproduction theory.

Thanks Stephen.

 

[RobC]

Mmmh, rethinking it, there's a complication.
If you lay the disc over the table, and the sun is let's say 45°, and you take the picture at 45°, the two readings (disc and grey card) should coincide.
But if, let's say, the sun is very high, and your angle of view is different, then the reading that the flat surface of the disc collects is for the light at an angle which is different from the lens angle with the table.
The two readings should coincide if you photograph the table from above, with the lens perpendicular to the table. That is, if you photograph the table as if it were a document. Only in that case the flat grey card collects the same light that the disc collects.

The flat disc diffuser should always be perpendicular to the main light source axis otherwise you are not using the meter as intended by the manufacturer.
The lumisphere is meant to be pointing at camera lens and not on main axis (unless it happens to be right behind the camera (which may create a shdow on the meter).

AND

with the lumisphere pointing straight up from table it would only be correct if camera lens axis was pointing striaght down on it.

AND

Spot meter reading should pointing straight down from above too.

And remember lumisphere uses 12% average as baseline and lumidisc uses 16% average reflectance as baseline

 

[RalphLambrecht]

its grey, not gray. They can't even get the spelling right.

Who s'they'?

 

[RalphLambrecht]

The flat disc diffuser should always be perpendicular to the main light source axis otherwise you are not using the meter as intended by the manufacturer.
The lumisphere is meant to be pointing at camera lens and not on main axis (unless it happens to be right behind the camera (which may create a shdow on the meter).

AND

with the lumisphere pointing straight up from table it would only be correct if camera lens axis was pointing striaght down on it.

AND

Spot meter reading should pointing straight down from above too.

And remember lumisphere uses 12% average as baseline and lumidisc uses 16% average reflectance as baseline

I'm making progress with my test on % reflection of the average scene but everything is pointing at 18% at the moment.

 

[markbarendt]

The flat disc diffuser should always be perpendicular to the main light source axis otherwise you are not using the meter as intended by the manufacturer.

The meter in flat mode simply measures whatever light source it's pointed at. I agree that it should be pointed directly at what you are trying to measure, but not just at the "main" light.

Duplexing as described by Dunn uses the flat mode with one reading pointed at the main light and one reading pointed at the camera that are then averaged.

Another example is in studio/controlled light situations. One measurement would be taken pointed at the window (main light) from the sitters position, a second reading pointed at the offside lighting, not the camera. In this example the meter is being used to check the lighting ratio so that the secondary lighting can be adjusted so that the subject's offside has the look you want. (In this case I typically use the main light reading to set the camera.)

 

[wiltw]

The flat disc diffuser should always be perpendicular to the main light source axis otherwise you are not using the meter as intended by the manufacturer.

But the reading with flat disc aimed at the windowlight source was 1/60 f/5.6 +0.6EV...about -1EV of underexposure.

with the lumisphere pointing straight up from table it would only be correct if camera lens axis was pointing striaght down on it.

yes, and I was standing on a chair shooting the 'art' from overhead, yet the shot was 0.5EV overexposed

AND Spot meter reading should pointing straight down from above too.

And this was pretty close in the the ideal exposure. I was standing on a chair shooting the 'art' from overhead,

 

[markbarendt]

yes, and I was standing on a chair shooting the 'art' from overhead, yet the shot was 0.5EV overexposed

Is your assessment here is based on the use of a digital camera?

 

[wiltw]

Is your assessment here is based on the use of a digital camera?

<heavy sigh> Every test I had ever done before with my digital camera revealed its ISO rating provided me with an exposure which put the 18% grey card exposure to be positioned precisely in the middle of the histogram -- smack dab in the middle -- between any extremes of 'black' and 'white' when metered with my incident meter. (Note in this photo the Tone Curve and the three peaks, with the middle peak between the other two peaks.)

So when I metered the 'flat art' set with the same incident meter, and I metered the grey card with my same one degree spot meter, I did not question the validity of my assumptions about digital exposure results, when I have used precisely those same two meters for decades for film exposure.

 

[Diapositivo]

wiltw, to clarify what Mark means regarding speed point, I suggest you read Kodak document H-740, "Basic Photographic Sensitometry Workbook", which explain the basics of sensitometry, and I certainly won't go a centimetre past that document as far as complexity is concerned

What Mark means is a well-known property of B&W negatives: by altering the developing time you alter much more the highlights than the shadows. One can imagine the characteristic curve as "pivoting" around a shadow point, on the left of the graph, where there is minimum density. The more the exposure, the higher the density, by a "law" which is defined by the ISO speed of the film but also by the development time (or agitation, or temperature). The curve can "pivot" around that shadow point at different kind of development and while the different development raises somehow all the curve, the effect will be more relevant to the highlights.

That leads to the "zone system" by Adams. By developing negatives one by one, you can alter the contrast and the highlight renditions of the image. That's because the development can alter the highlights much more than the shadows. So you control the shadows with the exposure, and you "control" the highlights with the development. In this manner you can obtain a negative which is more contrasted, or less contrasted, than the original scene, and always print on the same gradation of paper with the intended result.
This is all very esoteric, very sophisticated photography. The Zone System applies only in Black & White, in sheet film (because you develop each shot individually), and is as far as I know quite a complication in a world of variable contrast papers. But that's only what I heard through the grapevine, I use slides, and I would like to go back to it.

[My example of the digital ETTR was intended to mean that it is a technique that uses a "non ISO" exposure to reach a certain result. It's not meant to be taken literally and transported in the analogue world].

Before we talk slides, we should talk very simple sensitometry. For a complete ignorant of the matter like yours truly, you can define a speed scale either by choosing a certain arbitrary density on film, and then measuring how much exposure it takes to arrive to that density (the higher the exposure, the lower the speed) OR by choosing a certain arbitrary exposure on film, and then measuring how much density that produces on film (the higher the density, the higher the speed).

There certainly are very many possible algorithm for defining film speed. The most famous are ASA/ISO, and DIN. There used to be others, created in the United Kingdom, in Eastern Europe, in Russia. Now the world set on the ISO standard which is basically the ASA standard.

If I were Mr. ISO I would define a certain density on film "around the middle" and measure how much exposure it takes to arrive there. Mr. ASA did things very differently. He chose a certain point at the near transparent end of the characteristic curve of the negative, and from the density of that point, he derived a certain speed, assuming, I suppose, that the rest of the curve was basically linear and the ASA number would describe the "entire curve" (or line) of the film even if it was calculating by extrapolating the very initial part.

As a completely ignorant person of the subject, I can infer that Mr ASA chose to measure density near the extreme left because that minimizes the differences in development. Even though the ISO standard certainly stipulates a certain "standard" treatment defined by the manufacturer, measuring on the left of the curve takes some complexity out of the tests, takes away some head-scratching.

Conceptually, though, given a standard well-known development, Mr. ASA could have chosen any density, and is possible that Mr. DIN did something completely different than Mr. ASA, considering that certain films (Vericolor III if memory serves) have a "different" speed rating in the ASA and DIN systems (meaning: they employ two different algorithms). (The difference was 1/3 of a stop but is relevant for what I am saying). And the aim of Mr ASA, just as the aim for Mr. DIN, is to actually show the behaviour of the film around the middle part of the curve. If Mr. ASA chooses to take a certain low density point as "speed point" he does it for some technical reason but not because he has Zone System in mind, so to speak! Mr. ASA does not think that the user will develop for the highlights, or use sheet film. He means to tell you the speed of the film all along its linear part of the curve so that Aunt Sue will get the holiday pictures with the same tones that she saw during her trip to that most beautiful wonder which is Rome (shameless plug).

Now, back to slides. Slides matter because all this talk about exposing for the shadows, developing for the highlights, compensating in print does not stick with slides and does not stick with aunt Sue. I insist: slides can be developed only in one correct way, and can be seen only in one way, there's no print and there's no "recover" of details, no dodging, no burning, the bunny must come out of the hat at first attempt.

With slides, a light meter must work exactly and very precisely as intended. And it does! So - I insist - there is, even "implicitly" in the ISO speed determination, a way to make the middle grey (and all surrounding tones of all colours) fall exactly where they are perceptually faithful. Yes the extremes of the dynamic range will not be rendered, or will be rendered with some faults. But the tones around the average MUST be perceptually precise on slides, and they are. So lightmeters are actually devices that allow us to know where the middle tone will fall, and they show that to us every day. And they must be calibrated for a certain, unknown but certainly determined by the manufacturer, shade of middle tone. And I would be very, very surprised if this middle tone wouldn't fall exactly where the human eye sees middle tone, and where the "world at large", as shown by a research conducted by Kodak and mentioned by Ralph, shows middle tone. That's 18%.

So let's keep the reasoning alive because there is a lot to be understood more precisely (I have got a couple of huge doubts that I will try to clarify with your help) by keeping slide film in mind. Let's forget B&W negatives for the time being.

 

[wiltw]

Thanks Diapositivo.

I am aware of the interconnectedness of exposure and development, as taught in the Zone System -- I have Ansel's book The Negative on the shelf behind me, 3' away,and have been developing B&W since 1962 or so (and also color darkroom since about 1964). The Zone system basis of film exposure I have applied to exposing color materials, even though I have not ever tried to apply contrast changes or processing deviations to color materials, it does affect how I 'place' my exposures if shooting a landscape, for example, just as I might do with B&W neg. While not wholly ignorant on the topic, in my 45 years in photography I did not recall ever hearing the term 'speed point', as I had only a practical level interest in sensitometry. I have read chapters on the topic in photographic educational tome. But I do not profess to be a true Zonie who exposes and then adjusts processing for a single shot, and then prints it, so I am not an Expert Zonie in spite of the fact that I have a view camera (monorail), my LF work has largely been confined to product photography on color precise emulsions like EPN (IIRC the emulsion designation which hasn't been available in years).

Appreciate the elucidation on ISO vs. ASA very much, as I had never read upon about similarities and differences...I merely noticed that the ASA numbers all seemed to become ISO numbers at that point in time, and am aware that some emulsions might have been ASA 320 vs. ASA 400 (Tri X) but not having insight as to the Why of that rerating by Kodak. My Kodak Darkroom Dataguide expresses everything in ASA, and Tri-X 320 Estar and 320 Estar Thick base and Tri-X 400 are separately listed. I did not notice if any emulsions when from ASA X to ISO Y, however, such as your mention of Vericolor III.

Going back to one text which I had previously read (apparently not with full memory of its contents!), it mentions in one place 'speed point' and says it is

"located at a density of 0.10 above base plus fog and the following formula is used:

ISO (ASA) = (1 / Hm) x 0.8

It goes on to say that "ISO (ASA) speeds are rounded to the nearest third of a stop using the standard values listed in Table 4-3...The determination of speed is as follows
Locate point m at 0.10 above the base-plus-fog desnity, which in this case is at a gross density of 0.20
Beginning at point m, move a distance of 1.3 in log units to the right along the log exposure axis
From this position, move up a distance of 0.8 in density units, and if the cirve crosses at this point
(±0.05) the proper contrast has been achieved and the speed may be computed at point m.​

It continues on and derives for an exposure of 0.00428, that the example is ISO (ASA) 200. In this text, authored in 1990 by three distinguished faculty and one professor emirtus of RIT, it never states any differences in numeric ratings of ISO vs. ASA.

 

[markbarendt]

wiltw Digital cameras are a cool way to test general ideas without burning film, I play with ideas there too.

But:

Digital cameras do a lot of processing in camera to develop a picture. Then the software used in computer adds another layer of processing, the screen shot in post 122 shows adjustments to brightness, contrast, blacks, saturation, vibrance. Your camera and Adobe may have even done those adjustments for you without your knowledge.

And:

Film and Digital use different ISO standards. https://en.wikipedia.org/wiki/Film_speed

My point is simply that when we want to talk specifics about how things work with film, we need to understand that film and digital really are different.

 

[wiltw]

wiltw Digital cameras are a cool way to test general ideas without burning film, I play with ideas there too.

But:

Digital cameras do a lot of processing in camera to develop a picture. Then the software used in computer adds another layer of processing, the screen shot in post 122 shows adjustments to brightness, contrast, blacks, saturation, vibrance. Your camera and Adobe may have even done those adjustments for you without your knowledge.

And:

Film and Digital use different ISO standards. https://en.wikipedia.org/wiki/Film_speed

My point is simply that when we want to talk specifics about how things work with film, we need to understand that film and digital really are different.

I shoot RAW, the camera does ZERO processing in camera. I do RAW conversion with Lightroom, and the only processing it does is what I instruct it to do. The values of Brightness and Contrast are my own standard settings that I had chosen which results in an appearance which I had experimentally determined to provide what my own film-experienced shooting expected to see as a result. My standard settings would reproduce the Macbeth Colorchecker chart with a faithful brightness and contrast and subjectively faithful reproduction of hues (saturation and vibrance). It is possible to derive a profile with measured objectively faithful reproduction of hues, but I have not needed that for my now-enthusiast level of photography...I haven't shot any textiles or fashions since my film days.

So while the derivation of ISO rating is different from film to digital, I am ultimately a pragmatist and not a theory driven sensitometrist measuring density values on film. I seek black blacks and white whites and 18% midtones in between those two extremes, regardless of my medium, and I find my incident meter to give me the right tonal values in combination with my standardized settings during RAW conversion with my digital, just as it allowed faithful placement of midtones on slide transparency.