Well, I had an unknown film over the weekend. It was 100' of Kodak 2575 High Speed Duplicating Film circa 1980. Bought at a camera show for about $4 for a lark as to see what it might be. I thought it might be related to 2475, which is a recording film that gave grain the size of snow balls. The box said was ok to handle under 1A safelight, so I presumed it was orhtho chomatic, or maybe only blue senstive. So if that was the case, maybe it was closer to fine grain release film? Unprocessed it looked white, like fine grain relase does.
Loaded 36 exposures into a cassette, stuck it in a camera and set the meter on 12asa. Ortho dupe films, high speed or not, are usually slow. Metered on a grey slide in a slide duper set up on the enlarger desk. The duper diffusion plate is illuminated by an MR-16 tungsten bulb I have set up for this sort of tests. I filtered the slide to daylight with a balancing filter, in case the tungsten is too red to mate well with the ortho's response curve.
Round 1 -Metering was f/5.6 at 1/30". Exposed 1/100, 1/30, 1/8, 1/2. Open the camera back after 5 frames in the dark, and take the exposed film and toss it into a tray of Dektol paper developer, and turn on the Red safelight I reserve for ortho film use.
Dektol will develop anything. Harshly often, but enough to get you started on a usable speed when you start with an unknown film. After 2' the film was uniformly black, save a bit of grey leader.
All fogged? Toss first test into fixer tray.
Round 2- White lights on. Pull 2" out of cassette. White lights off. Pull another 2" out of the cassette unexposed. Toss into dektol. The flashed leader goes clear, and unexposed stays black. A light bulb goes on in my head. Oh - this is positive to positive film, and was pre-flashed in manufacture. We are working on the part of the HD curve over the shoulder where the reponse curves down again!
Round 3 - Change target slide to one I have of a MacBeth colour checker chart. Shoot it f/5.6 at 4, 20 and 80 seconds. Pull and precess next 6" of film in the tray. The result is that 20 seconds is weak, 80 seconds is overexposed. The film appears to be blue sesnitive only, based on the squares of the Macbeth chart that show density. I am getting somewhere finally.
Round 4 - Pull the colour correcting filter since the film is blue sensitive only, and expose wide open f/3.5 on my macro lens, for 1, 2, 4, and 8 seconds. It turns out that expsoure between 2 and 4 seconds looks best. the final results needs to be refined in a less severe developer than Dektol, and projected. It looks like the film is still viable, but will not be used in the field. Speed works out to less than ISO 0.5. It does appear to be grainless so far.
I am thinking this might be the right product for me to use to shoot copy negatives with. I have negs from my early years in photogrpahy that hold precious scenes, but could really benefit from some intensification efforts. My experiences with 35mm intensification are that it is not always a sure thing. I would like to have a dupe before the original goes into my intensification regime. This product shoud fill the bill.
I hope this play by play gives you ideas on how to quickly test a totally unknown film to get you close to a more refined second roll effort. So far this effort went though 24" of 100' of film.
The same night I shot about 8 test frames on the MacBeth chart each of Ektachome 160T, and Ektachome Plus 100 that are also at least 10 years out of date 100' rolls that I am working on trying to calibrate. These I taped end to end with film splicing tape and loaded in total darkness onto a stainless steel reel, and placed it with other reels that are piling up in a capped daylight tank awaiting processing. I will process them tomorrow the other backlogged slide films.
The colour test slide results will be reviewed as to thier current effective speed by looking at the five white to grey squares at the bottom of the Macbeth chart. The exposure out of the bracket of times taken that looks best is then reviewed for colour casts with colour print viewing filters and a loupe over a daylight balanced light box.
Often old slide film takes on a colour cast that can be corrected by fitting a Cokin filter holder with the right Wratten filters set on the camera to counter the worst of the cast. The balancing filters and whole grey test neg is then put into the slide duper, and the camera film speed is adjusted until the metering matchs at the aperture and time used for the best looking original exposure. That gives you the new speed with the filters in place
I then write this on each cassette I wind off, and put the needed Wrattens into a Cokin 194 gelatin holder that I have for the old Cokin filter systen that I have acquired over the years.
There can be 'crosed curves' with old film, that colour correction filters or post processing scanning cannot fix (at leats to my level of scanning skills).
Then it is a question of where do you want to place the cast to use it creatively. I usually strive for balancing for white in the highlights, and can usually live with colour shifted shadows when shooting slide film.
Partially unscrewing crossed curves is usually a task best accomplished by reading off the density of the primary red, blue and green chips of the test chart for a range of bracketted exposures once the new efefctive speed is found on a densitometer. The measured values are plotted on a log plot and thus one can plot and read from the plotting the new (old) film response curve, and how to best fiter to partially correct for it.
