Also use a 80A filter to convert the enlarger light to daylight.
Wow! So that explains why my Panatomic-X seems faster.
Originally Posted by Photo Engineer
Because my platen is flat... Step 16 (approximately the speed point for Panatomic-X) is 5% closer to the light than Step 21 (typical 400 TMY-2 speed point). I can sketch the layout on a piece of paper and measure it with a Stanley tape measure. Doesn't take special equipment to prove the point.
While 5% only causes me mild amusement, I bet this really bugged the serious scientists.
Kirk, thanks for bring up the daylight conversion because while the exposure problem is solved with a $95 meter, another important aspect of the test exposure that is frequently missed is the color temperature of the light source and how it factors into the determination of film speed as this excerpt from Nelson's Safety Factors in Camera Exposure illustrates.
Originally Posted by Kirk Keyes
"A new formula for speed can be derived which will make use of the 0.1 fixed-density speed criterion and will also provide the desired safety factor of approximately 1.2. If a specification is adopted requiring development to a ΔD of 0.80 or an average gradient of 0.62, for example, the log E difference (ΔX) between the two types of speed becomes 0.29, and the exposure, Ed, at a density of 0.1 above fog becomes 1.9 times greater than the exposure, Es, at the fractional-gradient speed point.
A revised form of Eq. (12), giving a new kind of film rating or speed that would provide a safety factor of 1.2, may be expressed as follows:
Speed = 1/2Es. (13)
Since Ed = 1.9 Es (Ed is the for the assumed development condition, the equation may be rewritten as
Speed =1.9/2Ed, (14)
or Speed = 0.95 /Ed. (15)
A change in the spectral quality of the light to be used in the sensitometer, from simulated sunlight to simulated daylight (sunlight plus skylight), is also contemplated which will have the effect of requiring a constant of slightly more than 0.8 in place of 0.95 in Eq. (15) in order to keep the safety factor at 1.2. If this change in light quality is adopted, the formula for the new photographic speed will be
Speed = 0.8/Ed (16)"
(or in today's terminology Speed = 0.8 / Hm)
Last edited by Stephen Benskin; 07-13-2012 at 01:10 AM. Click to view previous post history.
I presumed that the silver-colored interior and the sample-holding chamber were somehow designed to make the light distribution more even. (And possibly the striped attenuator, laying in the bottom, was a factor; all of my testing used one of these.)
Originally Posted by Bill Burk
When first working with a new EG&G sensitometer (in my job, around 1980?), I was skeptical about eveness of lighting, due to the flat sample holder. I had previous experience with a Kodak "process control sensitometer," where the sample holder was curved, following a radius around the filament of a lamp. (New lamps were calibrated with respect to both operating amperage and location of the filament; the sensitometer allowed such adjustments.) So the simple appearing EG&G unit, with a flat sample holder and fixed-position flashtube seemed a bit shaky.
We did shake-out tests in all sorts of configurations to test for uneven lighting and consistency. We ran wedges in both directions to test for processing problems, and made special wedges, sandwiched between fixed density strips to detect light falloff. Our conclusion was that the EG&G was perfectly adequate for our purposes. It turned out to be a real work horse.
Stephen, are you saying that the EG&G units are intermittent?
Originally Posted by Stephen Benskin
I don't believe this is true, unless one used multiple flash "pops." Granted, the flash may not be constant intensity (quickly up to peak power, then falling off for the duration of the flash), but I'm not even sure this happens in an EG&G unit. Even if power does fall off substantially, this still doesn't seem to meet the definition of intermittent (I mean a general definition, I don't believe that any of the film speed standards elaborate on this.)
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Wow - I didn't have the chance to check the thread last night. Lots to read.
A couple of quick clarifications here:
-Leigh B and others: Re contacting, the purpose here is to remove flare from the test. This is actually the precursor to another thread about testing and flare, and how one should really test film for his/her purposes. There are a lot of different ways of doing it. But actually now I'm thinking perhaps it would have been better to start with that thread.
-Re colour temperature: I prefer to test with tungsten (in this case it would be quartz halogen so perhaps not ideal) rather than daylight as much of my work is made under those conditions.
-Re enlarging meter, I have the Darkroom Automation meter (Pyro version). But I have not used it before. I originally bought it for Pyro densitometry but haven't used it yet. I don't use an enlarging meter when printing so the meter has sadly been sitting idle.
-Stephen: I probably should have first posted the flare/testing procedures thread I mentioned to you a few weeks ago before asking how to use my enlarger for contacting, but I haven't had the chance to write it up yet. So I figured in the meantime it would be helpful to at least figure out how to do a contact test.
I have to read through what everyone's written here in detail.
This is what the standard has to say.
ISO 6 Photography - Black-and-white pictorial still camera negative film/process systems - Determination of ISO speed
5.3.2 Type of sensitometer
The sensitometer shall be a non-intermittent illuminance-scale type.
I'm looking into my interpretation of what constitutes a non-intermittent sensitometer. So far, it's looking like my attributing it to the light source and not the exposure is incorrect. Theory of the Photographic Process 3rd edition talks about intermittent and non-intermittent sensitometers (I need some time to carefully read through it). It doesn't mention xenon flash so that part isn't helpful. The Encyclopedia of Photography does say that "no standards exist for such sources as flashlamps and fluorescent lamps." (edited later) I currently don't have the standard in front of me, but I believe it states incandescent for the light source, and maybe that's what the guy from Kodak was thinking when he dismissed my data out of hand.
Last edited by Stephen Benskin; 07-13-2012 at 08:52 AM. Click to view previous post history.
Todd-Zakia sketch an intermittent illuminance in their diagram of the monochromatic sensitometer. A sector wheel "constructed so as to produce a stepped series of illuminances on the sample when the wheel is rotated sufficiently rapidly to avoid the intermittency effect."
Originally Posted by Stephen Benskin
I think they are ruling out the spinning sector wheel as far as speed testing in the ISO standard.
OK. Sounds like a solution looking for a problem.
Originally Posted by Michael R 1974
Is this a BTZS thing?
“Wise men talk because they have something to say; fools, because they have to say something.” - Plato
Ilford makes a very nice on-easel meter as well.