densitometry coach?

[Murray]

I am trying to get together a game plan for testing of oddball films I could not resist acquiring (aerial, xray, microfilm and graphic arts). Kind of like FAS instead of GAS.

I have some low gamma developers identified to control contrast.

Where I am confused is what step to do first when I don't yet know a film ISO or a development time in a given developer.

I think if I knew the development time I could expose Zone I and V or VIII and an unexposed strip and figure out a film ISO.

Do I do something like determine the time for base + fog to get the processing time first?

I'm not worried about printing yet...just the film.


I have an XRite 301 transmission densitometer.

Thank you

Murray Leshner
Holland MI

[snuck]

Well I can save you the trouble with Kodak Graphic arts film. Kodalith, 16x20 sheets, process well with constant agitation 6 minutes in 1:50 rodinal, shot at a rated ISO of 6. That's constant rotary processing.

Results are contrasty however, so if anybody has a better idea, I'm all ears... That said, there still are 'continuous tones' from this methodology'..

Cheers

[Anupam]

Where I am confused is what step to do first when I don't yet know a film ISO or a development time in a given developer.

I think if I knew the development time I could expose Zone I and V or VIII and an unexposed strip and figure out a film ISO.

Remember that exposure determines shadows, development determines highlights. Hopefully you know a rough ballpark ISO (like if it's 50 or 1600). Then the key is to expose at various EI values around that for zone 1 and develop it. Development time is unimportant - it doesn't affect the shadows very much. So let's say you have something like an ISO 400-ish film. Expose at EI values of 200, 250, 320, 400 for zone I and develop along with a sheet of unexposed film. The unexposed film will give you your Fb+F and after that you are looking for .1 above Fb+F. That's your EI - simple!


Okay - now to determine development time. Shoot at the EI you tested and expose a few sheets of film for zone VIII. Give them different development times. You are looking to hit about 1.35 above Fb+F for diffusion enlargers and 1.25 for condensor enlargers. Whichever sheet gives you the correct density will give you your development time.

A little fine tuning might be required - I usually shoot one final set at both zone I and VIII and run it through and check densities on both to see if they are at .1 and 1.35 above Fb+F etc. But that's pretty much it.

[Murray]

Great !

Thank you both. This is helpful.

I have data for some and not for others...

[Nathan Potter]

Snuck, some years ago I processed Kodalith Ortho in Dektol to obtain a long density range. The disadvantage with the graphic arts films though is the propensity toward adjacency effects ( what they are designed for). Any dust that might be imaged is magnified on the film even with a long range tonality developer. I had to work in a laminar flow hood to obtain pristine negs but with Dektol I could produce some impressive results.
I'd have to check my darkroom notebooks for details but I know I used Dektol at 1:2 or 3. and tray development with red safelight inspection during the development. I assumed ASA 6 EI.

Nate Potter

[nolindan]

I am trying to get together a game plan for testing of oddball films I could not resist acquiring (aerial, xray, microfilm and graphic arts)

Cut them into 4x5 sheets and take pictures or make contacts of a transmission step tablet at ASA 2 (it's likely the film won't be any slower), placing the clear portion at zone 0. Take a half dozen exposures or so and develop them in a tray, pulling them at 4, 5, 6, 10 ... minutes (or whatever scale makes sense). Adjust ASA and developing times and repeat if things go off scale.

Some part of the step tablet will produce an H-D curve, find the film with the straightest and lowest contrast (for lith film) or desired gamma (depending on what the negative is to be printed with/on) curve. Quite often the low contrast curve isn't the straightest. This becomes the standard developing time.

For very contrasty film determining the EI for ~0.6 OD (18%, Zone V) may be a better choice than the standard 0.1 + B+F method.

As a bonus, you also pick up data for N-2 ... N+2 exposure and development.

[ic-racer]

Personally I think a densitometer is of limited use for development control without a sensitometer. (of course I have two sensitometers...)

Anyway, just expose a strip of film with the sensitometer and send it through your process. Measure the gamma or contrast index with your densitometer and adjust development time about 0.6 or so (with a diffusion enlarger.)

Better yet, measure the gamma or contrast index with a known film/developer time combo that gets you good results and duplicate that gamma or contrast index with the 'unknown' film. That the way I do it.

PS: don't try to use the sensitometer for EI measurements, do that 'in camera' and check 0.1 log with your densitometer.


If what I typed does not make sense try this: It should be required reading if you own a sensitometer or densitometer (you really need both :) ): http://www.kodak.com/US/plugins/acrobat/en/motion/education/sensitometry_workbook.pdf

[Murray]

Thanks. That handbook has questions and answers I haven't thought of yet.