As Matt noted, the speed increase is so small that it is not noticeable and can only be shown it best. In real life, there is no noticeable difference.
Sirius, that's wrong.
Not only middle gray value and optimal EI change with extended development: even shadows do, in a small amount.
You can see it yourself the day you decide to do that homework.
Speed depends also on the developer.
Juan,
Extending development does not increase film speed (aka sensitivity to light) appreciably.
It does alter the characteristic curve though, which can result in more usable results from exposure that is less than optimum.
You, who has all the sensitometers in the world (except maybe a Kodak Type 1B), shoots a plain target?
Now that I think about it, I don't believe I know what you mean by "0.1 log d". Can you explain?
Understood. And thanks. So, using a densitometer, one measures a density 'D' of the negative uniformly exposed at Zone I, computes the product 0.1*log D .... and does what exactly with that number? I think I'm missing some context or background here.Those are the technical units of the readout of most sensitometers and the units of the Y- axis of the H&D curve. D is density which is the inverse of transmission. That is why the H&D curve gets higher to the right as LESS light can pass through the film.
Juan,
Extending development does not increase film speed (aka sensitivity to light) appreciably.
It does alter the characteristic curve though, which can result in more usable results from exposure that is less than optimum.
John Finch has an informative channel on Youtube named Pictorial Planet .
He has also written an excellent book called The Art of Black and White Developing.
He explains in detail a simple way of determining film speed for your chosen developer, and in the second video he shows how to determine the developing time for correct contrast.
Have a look at the links
I am trying this method as we speak.
I shot a test roll of Ilford Pan F in 35mm and a roll of HP5+ in 120mm
The negatives are drying at the moment. I will do a Dmax test using the fb+f negative on silver gelatin paper and on Agfa Ortho Green xray film to find an iso.
@Andrew O'Neill
Would you be able to read these negatives with your densitometer for me as well?
I would like to know what comes from this angle as well!!!
But I'm not bringing my densitometre to Timmy's!
Too bad - that might be the definition of Canadian, photographic nerdism!
It'll cost you one apple fritter.
Too bad - that might be the definition of Canadian, photographic nerdism!
Only one!!?!!
I was thinking more like a 6 pack
I have two rolls to measure
Understood. And thanks. So, using a densitometer, one measures a density 'D' of the negative uniformly exposed at Zone I, computes the product 0.1*log D .... and does what exactly with that number? I think I'm missing some context or background here.
Are you trying to kill me? 6 pack is fine, but TWO rolls??!!
Understood. And thanks. So, using a densitometer, one measures a density 'D' of the negative uniformly exposed at Zone I, computes the product 0.1*log D .... and does what exactly with that number? I think I'm missing some context or background here.
The Arithmetic film speed is 0.8 (a constant) divided by the Arithmetic exposure the film received at the point where it has developed to 0.1 density above filmbase plus fog.
A 400 speed film takes -2.7 log meter candle seconds to meet that measure when developed to the ASA contrast parameters in standard developer like D-76.
Antilog of -2.7 log is 0.002 Arithmetic meter candle seconds.
So plug into the speed formula 400 = 0.8 / 0.002
0.1 density is an easy density to measure. You don’t actually “do” anything with it. But it’s near the area of dark shadow, key black of the print where detail is just emerging. It’s about a stop of exposure (0.29) above the 0.3x average gradient point (where the slope of the film curve flattens out to be a third of its average). 0.3x average gradient is the speed point. That’s the point found in Kodak studies where ordinary people judged prints (sorted a bunch of prints made from negatives with variety of exposures into just acceptable, good, excellent, unacceptable) and picked the first excellent print.
It’s traditional to graph exposure on the X-axis in logarithmic terms decreasing exposure as you go right-to-left and the Y-Axis is density in logarithmic terms increasing density as you go up from bottom. That makes X and Y the same scale. You would get a curve of 45 degrees if the negative was developed to give one to one density increase for exposure increase. Unity contrast is a special purpose, for example negative copying. For regular photography you want to go up one for two across (0.5 contrast index). That fits normal subject luminance range on a negative that doesn’t block highlights. That’s a decent contrast for normal: 0.5 to 0.6
Quite a delay here, sorry to take so long to come back - I wanted to try an experiment to reduce flare. To that end, I shot a new test negative and developed it as before. For the test exposure I used a larger target and a longer lens (with a smaller acceptance angle) so that I could shoot from farther away from the target: about 5' away from the camera. I used an extended lens hood, and shot at sunrise, when the target was just about level with and perpendicular to the sun's direct rays. I reasoned that these adjustments would reduce the number of off-axis rays entering the lens. Also, instead of a white target I used a grey matt board.I was going to say, you’re flooding the interior of a dark chamber with light to make a contact print. There’s no flare in this scenario because all the light is even and the image is formed in that contact sandwich.
But there is off-axis light hitting the walls of the bellows increasing the overall exposure, that’s flare. So yes you could be getting increased expose above what you estimated.
I realize that attributing the difference in FB+F to flare doesn't fit. I measured FB+F in the blank patch left on the negative by the taped patch on the stouffer step wedge, and the density was 0.1 both the July and the May test shots. The rebate measurements were different - from each other and from the tape blank - in the two test negative runs, and I used those in my plots, to maintain continuity with earlier tests. Now it seems to me that I should have used the tape blank.Quite a delay here, sorry to take so long to come back - I wanted to try an experiment to reduce flare. To that end, I shot a new test negative and developed it as before. For the test exposure I used a larger target and a longer lens (with a smaller acceptance angle) so that I could shoot from farther away from the target: about 5' away from the camera. I used an extended lens hood, and shot at sunrise, when the target was just about level with and perpendicular to the sun's direct rays. I reasoned that these adjustments would reduce the number of off-axis rays entering the lens. Also, instead of a white target I used a grey matt board.
Metering was with the same Sekonic as before, which I had adjusted to match my Minolta Spot M (post #45)View attachment 310308.
Attached, a plot showing the new curve - in black - and the curve from the last plot I showed a few weeks ago. The FB+F+0.1 value for the earlier test shot was 0.27, and for the current shot it's 0.21. A difference due to flare, perhaps? The right-angle apex of the ISO triangle is still about 1/3 stop away from the nominal Zone V value. I'm thinking that if I shot this film at ISO 125, the alignment might improve.
Tom,
If the step tablet was sandwiched over the film, then flare wouldn't be a factor. It's flare free. If you are wondering about the difference in Fb+f between the two tests, that sounds like fog. You need to make sure a the Fb+f section measured receives zero exposure.
The two test appear to have about the same gradient. The displacement is from exposure. The test from May had more exposure than the recent one. If there was any extraneous exposure striking the area of the film where you measured Fb+f, then that part would have received more exposure in the May test and would have a higher density than the recent test. Process a blank sheet to guarantee a baseline if you are wondering what is causing the difference.
Stephen
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