> How do you evaluate your tests? which densitometer do you use? Which camera (how do you determine that your shutter is correct before testing)?(posted 8326 days ago)I start by calibrating all meters to "Sunny f16" using a Wallace Expo-Disc. I believe "sunny f16" or, 1/EI @f16 for an exposure in direct sunshine with the sun high in the sky, to be valid for my area; tropical residents may need "sunny f22" or thereabouts while residents of the far north may need "sunny f11."
"Sunny f16" exposures result in the expected densities with a variety of film types including traditional b&w, C-41, E-6 and K-14.
So...why calibrate to "sunny f16" and not something else? The short answer is that there isn't anything else. There is no "industry standard." So I use what's consistent and consistently available.
The Expo-Disc is a dense diffusion disc that transmits 18%. Although the "standard" such as it is is 13%, trying to achieve a 13% reflectance by holding a Kodak grey card at the specified angle to the light, not shade it or not get glare off it, creates more potential errors. Someone with more knowledge of mathematics than me could calculate the difference between 13% and 18% reflectance/transmission, but I believe it to be no more than 1/3 stop.
For shooting test strips, I use a camera that has an electronically-timed shutter that I tested with a Calumet shutter tester a while back; it turned out to be consistently within 1/3 stop of the set speeds throughout the range I use for testing. I always use the same lens, beginning two stops down from wide open to avoid losses due to vignetting or falloff at wide apertures.
I shoot a series of test exposures through a range of 14 to 15 stops.
Developing the film is straightforward, either in a Jobo machine or using hand inversion tanks. BTW, I've gotten consistent changes in EI for the same CI with a couple of films on the order of +/- 1/3 stop when comparing continuous rotary agitation with intermittent inversion agitation.
I read the negs with an Eseco TR-90 densitometer, which is regularly calibrated to a step wedge, and plot the curves on paper. Not particularly automated. ;-)
For several years I've occasionally compared my results with three people who also do the same sort of testing as a "reality check" and we've usually agreed sufficiently well.
> sacrifice shadow rendition for film speed, which makes the film better to sell.
While I'll agree that it's easier to sell a film that's labeled EI 400 than EI 250, I don't think it's a valid assumption that shadow rendition is somehow being sacrificed. I believe it would be much more confusing to customers and users if the film needed to be labeled several speeds according to which developer is used; for HP5+ for example this could be anywhere from around EI 100 (PMK+) to EI 640 (Microphen). > To sum up: I am fairly convinced that I can prove my statements about film speed with the test I made.
I don't think it's a matter of proving anything; it's necessary to recognize that equipment, materials and methods vary and the results one person obtains may be somewhat different than the results another person obtains, all caused by variations and tolerances in manufacturing, calibration, procedures and above all, what constitutes a "good image."