Kodak grey card usage
-
A
- Thread starter RobC
- Start date
Recent Classifieds
-
For Sale FS: Tamron 150mm f/6.3 Lens
- Started by B.S.Kumar
-
For Sale FS: Royal Soft Focus 150mm f/4.5 Lens
- Started by B.S.Kumar
-
For Sale Kodak Aerochrome 1443 Offcuts, the last I'll be selling
- Started by MCB18
-
For Sale 9 Rolls FUJI Fujifilm SUPERIA PREMIUM 400 27 exp 3 pro packs
- Started by orbitaldebris
-
For Sale Nikon Nikkor-H 85mm f1.8 AI'd
- Started by Oldwino
Forum statistics
If your past post is a reaction to my comment about 'zero processing' I know well enough that there has to be some processing to equalize the electrical response of the three pixel colors, to balance the image to a neutral response under 'daylight', make ISO 100 rating perform 'just like ISO 100 film', etc.. But apart from very low level things like that (like gamma) there is not a fundamental assumption about contrast and brightness or color saturation by RAW convertors (Canon DDP attempts to mimic the settings that the camera uses to create preview JPG data which is embedded within the RAW file, the only exception to that statement.) I even have to select a contrast curve vs. a linear response, and I can alter the profile of the curve.
The point I am making is that digital is different.
Sometimes very different. Once the analysis has been done digitally, the analysis will need to be repeated on film. So why bother with digital in the first place other than to just play with it?
Pretty much.
Perhaps both of you can enlighten us all with specifics of how 'digital is different' and behaves in a manner inconsistent with film. BTW, reciprocity does not count among the differences.
- Joined
- Feb 9, 2010
- Messages
- 9,290
- Format
- 4x5 Format
Enjoyed your storytelling... maybe I can fill in part of the story as I understand it...
When dry plates came out in the late 1800's "Standard Extremely Rapid Dry Plate" didn't mean much. Hurter and Driffield drew the first line in the sand when they picked natural logarithms as the units of density and exposure. On their graphs they drew a line following the straight-line part of the curve and extended it straight to the exposure axis. That point they called "Inertia" and used it to rate the films and plates. So a "Roebuck's Extra Fast Dry Plate" would get a speed of H&D 200 (something like ASA 10). Having H&D speeds was like having "Consumer Reports" on your side to keep you from buying into the hype.
When films started to have long toes, they were getting bad ratings by H&D so a new method was needed to give these new films a fair break.
Mr. ASA found a spot way down on the toe that he knew was the absolute minimum (the 0.3 gradient). Mr. DIN didn't deny it but said the math to find that point was too complicated. For a long time (maybe even before H&D) Mr. DIN said develop as much as possible and find 0.10 above base and fog. I'm not sure who was the clever one who found the compromise and said something like "hey... if you bring down development to the point where you can fit a standard picture onto a standard paper, then you could stop arguing over 0.10 or the 0.3 gradient because they are sort of locked into each other."
- Joined
- Feb 9, 2010
- Messages
- 9,290
- Format
- 4x5 Format
Digital can have a true straight line tone reproduction, where film always has a bit of an s-curve.
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.
It's about the parameters of the speed determination method of both B&W negative and Color Reversal and the relationship of the different speed points to the metered exposure point. I could explain it but it would take math and math tends to upset people for some reason.
Well, while they both accept input of light through a lens, they use very different subsets of the rules of physics from there forward.
Chemical/Physical processes, like how certain wavelengths of radiation affects the silver in a film and how that silver behaves when dipped in certain chemicals, are constrained by rules we can't change.
Digital processes can't break the rules of physics either but the rules that define a digital image are fully contrived at the whim of man. If a software engineer were to pick middle gray to hinge all adjustments on there's no reason they couldn't. Film can't do that.
Last edited:
OK, I can loosely interpret the S-curve vs. Linear in this manner:
When film is exposed, it is inherently more contasty than Digital...in digital I can alter the Tone Curve and make it more contrasty than inherent response. In film I can overexpose and underprocess to make it inherently less contrasty than inherent response (Zone technique).
That is somewhat like the inherent difference of transparency vs. neg, or processing Tri-X in Acufine vs. HC-110 dil B 4 decades ago.
So it is different, I can manipulate somewhat. I adapted technique of metering and exposure to different kinds of film, but 18% grey was still 'in the middle' if I exposed and processed each properly...the fundamental exposure was essentially the same 'per ISO rating' even when inherent contrastiness or DR of slide vs. B&W neg were quite different. And so...???
if you stop trying to compare incident meters with reflection meter, throw your grey card in the bin, then all your problems and worries about exposure will disappear. You will learn to interpret your meter reading and adjust accordingly as an instinctive action.
On the other hand, if you are a perfectly able bodied person who thinks they need a crutch to walk with combined with two measuring sticks one of which is slightly longer (or is it shorter?) than the other and you can't see why they never quite match each other, then you are destined to be a pathetic paraplegic for the rest of your life by your own choice. That is not an intelligent choice to make. Is that you, just so we know?
On the other hand, if you are a perfectly able bodied person who thinks they need a crutch to walk with combined with two measuring sticks one of which is slightly longer (or is it shorter?) than the other and you can't see why they never quite match each other, then you are destined to be a pathetic paraplegic for the rest of your life by your own choice. That is not an intelligent choice to make. Is that you, just so we know?
Last edited:
Speeds fluctuated from batch to batch. Eastman almost went out of business when a batch had zero sensitivity. One of Mees' first jobs was to find the reason. It took him and Shepherd about a decade to find the answer. The inconsistency came from the cows used to make gelatin. More specifically, what type of cow and what they ate. I believe the greatest sensitivity came from Jersey cows that ate mustard plants. Mees once said that if cows didn't like mustard, there wouldn't be photography.
All of these threads have been interesting, but this is truly the bottom line. Especially if "and learn how to use the meter(s) correctly" is added.
Im not sure about the able-bodied crutch user, though. I'm still pondering that.
No.
Neither has an inherent contrast defined by the rules of physics.
Digital and Analog do though each have their own separate ISO standard for determining the sensitivity/exposure speed they can claim and that standard has certain rules that specify contrast.
In the wild though no one/no company is bound to use the ISO standards for contrast.
Digital and analog require different standards because they don't work the same.
Last edited:
I often wonder why ISO standardization wizards didn't think of using a different naming and numbering nomenclature. I understand being backward compatible but if the are different they ought to be different.
I think the backward compatible idea is on the right track but I don't see that as being tied to film. Light meters measure light and suggest lens and shutter settings, so the hardware in front of light sensitive medium.
Mark, I don't think there is a standard for contrast.
- Joined
- Jul 14, 2011
- Messages
- 13,928
- Format
- 8x10 Format
I always walk with one stick longer than the other. It helps on steep hills. And I once measured the diameter of a giant aspen tree using these trekking poles. But as far as measuring photographic subjects, I haven't bothered carrying a gray card in the mountains for the last thirty years at least. That kinda sums up my opinion of this whole subject.
I think you are normal, Drew. I asked, in one of these threads, who still uses a gray/grey card... and I don't recall a single person responding in the affirmative.
Thanks Stephen, I stand corrected on the specifics.
Where I got that thought was not from reading the standard but from here https://en.wikipedia.org/wiki/Film_speed
That article is also where the thought of centering adjustments on mid-tones comes from, this is from one of 5 ways the digital speed can be determined in the standard.
A short outtake here:
In this case the digital camera can be tied specifically to and or centered on 18% gray rather than having a specific relationship to the threshold of usable sensitivity.
It does seem to me though that in order to turn raw data into an image, that the tone reproduction needs to be defined. https://en.wikipedia.org/wiki/Raw_image_format
Last edited:
RobC, is that aimed at me??? I have made it clear that reflectivity of the grey card introduces enough variability of reflected readings off grey card, that anything 'matching incident' is purely coincidence.
I have done enough metering comparisons to know coincidence happens sometimes, but it does not happen other times, so any difference in reflected vs incident reading is somewhat shrugged off...it is inconsequential, for example, when I employ spot metering of highlight and shadow and average the two readings and assess if the DR fits within my film or digital camera DR. I can assess the difference between the spot average method vs. incident, and know the offset of the actual exposure from the incident reading, so that I can bring everything back to its INHERENT TONALITY in the darkroom or via digital editing.
If you recall, I have repeatedly pointed out middle grey as the middle of a number of tonal step wedge scales, having NOTHING necessarily to do with being a target for reflected light metering (which seems to be argued about what is the right tone to meter). I use it as the center between apparent black and apparent white -- regardless of the media, which is how it was originally defined by Munsell and the color system used in the world (for non photographic purposes). No matter what methods have to be employed for different media, the end goal is 'visual middle of scale' for faithful rendition of the midtone. That different contrastiness in film causes the toe or shoulder to be different, affecting low tones and high tones in their appearance, my midtone stays accurate for any contrastiness level.
I can say without a doubt that digital colour correction moves are identical to enlarger colour correction moves. a 5 yellow change is the same if you are using an all digital platform vs an colour enlarger.
Over the years I have been amazed at how close both systems can match each other.
Well... I'll be taking some photographs today... and metering with a lot of new-found insights and knowledge... but little change in methods.
Methinks my comments are taken too literally in this comparison of film vs. digital.
If I take a digital photograph, the red line is less contrasty than the curve...I can see that effect, and LR even calls the curve 'moderate contrast' or 'high contrast'. That was the point I was making. If I have a toe and a shoulder, far more things are perceived as 'black' or 'white' than the reality of the tonal level...we have some degree of control in the darkroom over the perceived contrastiness, just as we can do this in digital postprocessing.
I don't care that digital may have its own ISO standard than film...the camera manufacturer engineers the response so that a rated ISO 100 behaves in a manner which appears similar to ISO 100...in the early days, cameras were critiqued because "ISO 100 in the XYZ camera really is ISO 125", for example. The camera manufacturers fixed these differences, so today they behave similarly enough that an old film photographer like me does not have to relearn photography entirely to shoot digital. The more I use digital, the more I perceive it 'MORE LIKE FILM' rather than 'LESS LIKE FILM'. Differences may indeed exist, but materially for day to day purposes, it is 'the same' with many parallels in the two worlds, so that most ordinary photographers care not about the invisible (or hard to notice) differences.
Last edited:
| Photrio.com contains affiliate links to products. We may receive a commission for purchases made through these links. To read our full affiliate disclosure statement please click Here. |
PHOTRIO PARTNERS EQUALLY FUNDING OUR COMMUNITY:  |