Here’s a paper graph. I measure 0.57 CI and just a tad short of ASA parameters.
@radiant you and I have been discussing where I think exposure falls vs where your nominal device exposure is designed to fall.
I continue to estimate the exposure which would cause HP5+ to meet 0.1 above base plus fog is -2.70 log mcs. The curve crossed 0.1 above base plus fog right between two of your tubes. But I estimate that actual exposure is 0.01 or 0.02 higher because you didn’t hit ASA parameters.
So I think the tube you labeled -3.056 is -2.76 or -2.77 and the tube you have labeled -2.9031 is -2.62 .
We can surmise why the effective exposure seems to be higher than the engineered exposure, but I think the factor(s) will reveal themselves as you do more and more tests.
Spectrum reaching the film could be “more actinic” than daylight through glass lenses of a camera (UV could be hitting the film? Does your diffuser pass UV?).
You have a chance to try R G and B separately.
Have you electronically isolated the LED’s so there’s no noise or trace voltage that could be weakly energizing the LED’s that are supposed to be off?
Of course since we are possibly off by a full stop, we don’t know how that stop is distributed… the 0.15 intervals can’t be 0.15 intervals, this may reveal that you have higher contrast than we measured
Another thing could be light leak in the device allowing some of the bright tubes to influence exposure of the low tubes. Do you have good segregation between each of the tubes? Could the circuit board itself be piping light?
Tape off the bulbs and pour a black ooze over the board.
Same with the backing behind the film.
Look at all the parts with your IR device. Are they “white”?
TMY2 is relatively insensitive to IR, there is a hard cutoff in near IR. I don’t know about HP5+
very cool! subtract .65 milliseconds from each exposure and away you go!
You’ll notice how close you are to the toe when you consider 7 stops of subject luminance range at 1600. The longer development time helps improve image quality down in the toe. A photograph taken at the 1600 setting might place shadow exposure lower than you planned.
Yes, at 1600 I'm close to toe, there isn't much room for error in exposure. On lower stop range, low contrast scene, then I'm more safe and on linear part. Of course this is possible becuase of this film+dev combo being really,really good.
Today I shot one 6-7 SLR/SBR scene with EI 400/800/1600 just to see if my theory is right that the film is working in linear. I overexposed a bit just to keep the EI 1600 from hitting the toe, but it doesn't really have negative effect as I'm just testing the linearity. If my analysis is correct I can print three similar prints with only adjusting the base time and while printing on same grade.
I've also kept logbook of my prints and analysed the printed negatives. I'm not sure what I can do with the data but as I grow the log I think I can see patterns. I have a bit same kind of data that you have in your graph, actually. Not that many points but at least meaningful shadow / highlight information so I know what has been the negative density range for the exposure chosen on paper.
Shooting a 400 film at 1600 is the same as rating the film at 400 and stopping down two. Rating a film at 1600 and opening up isn't the same as shooting it at 1600. You will be misinterpreting the results.
The example you have is a good looking image, but it has stylized lighting. With exterior scenes, we have a internal idea of how they should look in sunlight and in overcast light. Interior light, especially stylized lighting, doesn't have such a criteria and consequently harder to judge the relationship between exposure and quality. That you are able to obtain a desired print with less effort does indicate better exposure / processing control.
Maybe I was not clear enough on my explanation. I of course understand what happens on 400->1600 change.
I think what happens is:
- my NDR area moves to the left, but stays on linear part where gamma is pretty much the same all the way
- without compensating on developing time I just get thinner negatives and I have to shorten my print times
- printing grade doesn't change
- with normal or low SBR/SLR I won't be hitting the toe, close of course and no margin for error
Those are my findings and I would like to hear did I misintepret the results?
You are correct. For a shorter than normal LSLR, underexposure will generally not have the lowest point of exposure fall far into the toe. A normal LSLR is another matter. As the speed point is located in the toe, normal shadow exposure already falls in the toe. Here's a two quad example.
Hmm, maybe I don't understand something (yet).
EI 400 Zone V is at -1.7 on film MCS. If we go 3.5 stops down (half of "normal" 7 stop SLR) we are then at -2.3. ISO 400 speed point is at -2.7. I don't see that falls into toe yet? Or well, it depdends on description of "toe" but for example my development at -2.3 there is good distance to toe. At -2.3 I'm on very linear part of the negative, right?
Maybe it's how you define toe or how it's drawn in your curve. 0.10 over Fb+f (Hm) is 1.0 log-H below the metered exposure (Hg) and not 1.05. Shadow without flare falls about 1.25 log-H. From a paper by Jack Holm,
You can add a bottom line to Paper LER, then slide the pair up and down like you slide the Subject Luminance Range to understand greater and less exposure.
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