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
No sweat, really thank you.Sorry Mark, I'm not intending to nit-pick. It just that this point has come up a few times lately. The ISO film speed parameters produce good correlation with the fractional gradient speed point using the Delta-X Criterion. It's only for determining the film speed, not for film/paper matching.
No it was aimed at anyone who is struggling with with why they cannot get meter readings from different types of meters or comparisons with grey card readings from one setup to another to agree.RobC, is that aimed at me???
It's amazing it provokes so many responses then.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.
The digital straight line in LR is part of a histogram and not comparable directly to an H&D curve.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.
No it was aimed at anyone who is struggling with with why they cannot get meter readings from different types of meters or comparisons with grey card readings from one setup to another to agree.
I don't use grey cards or incident meters and have no problems. If you know your film and one meter (I opt for a spot meter) then thats all you need for accurate meter readings and tone placement. Given this it seems pointless to be concerend about what appears to be inconsistencies between meters and readings. Simplest by far is throw out the things and processes causing the inconsistencies. ie. grey cards and incident verses reflective comparisons which achieve nothing.
The only thing a grey card is good for in my book is putting a neutral gray in a test shot to get colour balance right or close when analog or digital printing. And with either print medium, neutral grey isn't likely to be best if you have skin tones to worry about so even that is a moot point. It may be important if you need exact colour matching for a clients product packaging or logo or some such, but if you are working to that level then you likely have a colour densitometer to check exact match anyway. A neutral grey may get you close quicker but isn't likely the final colour balance reuiqred since film response is so different from film to film anyway.
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.
There is no hard and fast answer to this question. However, what you should know is that if you are wet printing to B&W paper then the paper requires an approx 1.3log film density range when printed at G2. That will give you a print density range of 2.1log of print reflection. Or to put it in simple terms, at Grade 2 a B&W print gives 7 stops of reflection density(when measured with a densitometer). So in a literal translation of the subject which just fits the paper, you would be looking for a subject which has a subject brightness range of 7 stops which is captured on film in a density range of 1.3log which prints to B&W paper exactly.I use a gray card
The Kodak reflectance card I use as a target (6.6 stops brightness range) has gray 18% background and patches ranging between white 0.0 and black 2.0. A test frame of this subject was made using Ilford Delta 100 exposed using spotmeter reading of the 18% background of the reflectance card and processed for normal contrast in ID11. I find this neg has a density range approximately 0.3 (= black 2.0) and 1.2 (= white 0.0). Based on these approximate density values is this a well exposed negative? It prints well. It seems to my limited knowledge of densitometry that there is a lot of unused density, film can go to density values of 2 or higher. Is this an underexposed neg? If so by how much? At what density values does the film "shoulder" begin?
Digital can have a true straight line tone reproduction, where film always has a bit of an s-curve.
Negatives don't have a middle grey. They have a transparency density. The assumption that will translate to a middle grey in a print is very dependant on how you print it.I must have expressed myself incorrectly or ambiguously. Mr ISO and Mr ASA are basically twin brothers. It's Mr. DIN who is different from Mr. ISO ;-)
What I wanted to stress, in any case, is that the "speed point" is "m", but the general use of determining the speed of the film is the overall speed. For a certain speed at point "m" there is a certain density at middle grey. Density at point "m" indirecty defines density at middle grey.
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.
You probably got 5 stops of range onto the film, with headroom for one more stop of light on the highlights end.
Here's how I figure it.
I have one of those grayscales and mine measures 0.04 to 1.95 which is really 1.91 and then suppose you develop to 0.58 contrast which I consider normal.
You have a density range on negative of 1.2 - 0.3 = 0.9
You can take the 0.9 density range on negative and divide by 0.58 contrast and arrive at the figure of 1.55 which is the subject brightness range corresponding to the negative density range. The difference between what you shot and what you got is 1.91 - 1.55 = 0.36 which would be attributable to flare that brought your shadow density to 0.3 instead of being 0.0 or 0.1 where you thought it would be.
So... This is a classic example which fits the model (though I projected some of my assumptions onto your numbers... you can confirm or counter).
In a standard 7 1/3 stop scene with something in the shade (yours is 6 1/3 all in the main light) the 0.36 flare would bring the subject luminance range at the film plane to 1.84 which would give you a density range on negative at 0.58 ... 1.06... which is all pretty reasonable.
Methinks my comments are taken too literally in this comparison of film vs. digital.
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. T
Negatives don't have a middle grey. They have a transparency density. The assumption that will translate to a middle grey in a print is very dependant on how you print it.
Even with slide film it depends on how you project it and the reflctivity of what its projected onto. You may be able to measure it in the slide. Or you may digitize the slide but then its down to your digitizing settings as to what colour you get. So who says the slide density is right? It really doesn't matter. Its what you do with it to view it that really counts.
yes but becasue your eye is constantly and subconciously altering its aperture you can never calibrate anything perceptually and get it right unless viewing conditions are always identical and even then its subjective. So you either do it by numbers or do a pratical test to see what you're actually getting which is what I do.Rob, slides have a middle grey, which is the perceptual middle between what in a slide appears white (let's say, the frame of a window) and what in a slide appears black (it might not be black, imagine the shade under a bush, but it's the "blackpoint" of the image, your eye sees it as black).
Whether you see it with a 150W or a 250W lamp, at 2 meters or at 5 meters, even though the absolute amount of light projected on the screen will be different, your "perception" of middle grey will remain the same, because your brain will "center it" between the two extremes of blackpoint and whitepoint which are present on the image.
If white is presente, and black is present, middle grey on the slide must fall where the human vision would expect it to fall.
And, more in general, if I project an image of "middle grey clouds" on the screen, I will perceive them to be the same middle grey both with a 150W lamp or a 250W lamp etc. (the intensity of the light on the screen will be different, but my vision will adjust for that, just like it adjusts for the different light falling on a print).
And If that wasn't the case, how could we go to the cinema and be satisfied by what we see? Things look natural because white looks white, black looks black, and middle look middle, IMO.
What wiltw and I are interested in is the behaviour of film, and of reflected light meters, when confronted with a certain shade of grey, which let's say is 18%, that we call "middle perceptual grey", regardless of the scene.
To make an extreme example, I might have a scene which is solely composed of something which I know has a 36% reflectivity and I want that 36% shade of grey to be naturally recogniseable in my final image. That means the SBR of the image is actually 0 EV or very near there, if it is enlightened with a flat light. The "middle grey" of the scene is 36%.
If I know that my light meter is calibrated to 18%, I know that, by reading the meter indication, and by exposing for 1 more step, I will obtain 36% grey which is the desired result, in my slide developed according to the well-known standard method prescribed by the manufacturer.
But in order to make that reasoning, I must know in advance to what grey is my light meter calibrated. If my light meter was calibrated, for instance, at an 8% grey, I would have to open more than 2 steps, instead of 1 step, in order to obtain that 36% reflectivity grey of my subject.
Thank you gentlemen, I'll take that as a no, it is not an underexposed negative. Printed on grade 2 paper the neg reproduces the reflection density range of the original pretty closely. This is basic calibration work to orient myself with a new enlarger and darkroom after a 20 year break.
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