The BTZS, was it ever useful?

frednewman said:

... I have changed the testing procedure slightly. Now you process a roll/sheet of film for 4 minutes and send it to me for reading. I'm looking for a specific contrast negative and if it is too contrasty or not contrasty enough you can adjust the dilution of your developer and try again. I started doing this because I would get the test back and the dilution of the developer would be too strong and all the tests would be too contrasty and you would have to start all over again. If they were doing their processing in a Jobo processor that's a lot of time. I really didn't like calling up a photographer and saying that the film you just tested was too contrasty and we are going to have to run the whole test all over again. It doesn't take a lot of time to do one roll/sheet for 4 minutes. I now send out 7 rolls/sheets with each test so we have 3 tries to get the right developer dilution. ...

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Fred

I can see the logic but never ran into this problem. Sometimes I end up having not quite enough contrast after 16 minutes, but then, I just go to 22 minutes to get that little bit extra.

Gradient vs development time graphs are non-linear. Unfortunately, sometimes the slope is increasing and sometimes it is decreasing. Consequently, judging the appropriate developer dilution from just one development time is difficult for most of us, unless we have done quite a bit of testing.

If I had to guess, I would say that a 4-minute development, resulting into a gradient of less than 0.35, is likely to need an increase in developer concentration if more than N+2 contrast is required and development times above 16 minutes are not desired. If the 4-minute development has an average gradient of above 0.45, one should think about a higher developer dilution or N-2 developments are impossible.

Then again, I had film/dev combos that had an average gradient of almost 0.5 at 4 minutes and still did not get more than N+1 at 22 minutes, because their gradient vs time curve is very flat (APX100 in Rodinal 1+50).

Ralph wrote

If I had to guess, I would say that a 4-minute development, resulting into a gradient of less than 0.35, is likely to need an increase in developer dilution if more than N+2 contrast is required and development times above 16 minutes are not desired. If the 4-minute development has an average gradient of above 0.45, one should think about a higher developer dilution or N-2 developments are impossible.

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And I am sure you are on the right track but I'm sure you meant

... a 4-minute development, resulting into a gradient of less than 0.35, is likely to need a [stronger concentration of developer]...


I totally get the idea, Ralph you have all the equipment in-house so you can control more variables.

Fred offers sensitometric/densitometric service to photographers without such equipment. In his case he's sending 7 sheets of sensitometer-exposed film to the photographer to process.

The 4 minute test is a sanity check. Assuming all the other variables are under reasonable control (temp, agitation, tank, etc.) -- developer concentration is a straightforward variable that can be tweaked and then locked down.

Then the photographer using Fred's service develops the series and both Fred and the photographer can expect reasonable data.

Thanks. I agree and corrected my typo.

Hi Ralph

I try to work with developing times between 4 & 16 minutes. The sequence of developing times used are 4, 5.5, 8, 11 & 16. This way normal developing times are usually between 6 & 9 minutes. If someone is testing film for platinum/palladium I sometimes extend the series - 22, 32 and even 45 minutes depending upon the results.

I've tried to use these procedures to keep the amount of work for film testing to a minimum. Film testing is like doing homework when you are in school and no one including us adults likes to do homework so the simpler it is the more likely film testing is the more likely photographer's will do it.

The original BTZS workshops that Phil Davis did were about 2 weeks. Everything was done by hand - this was before the plotter program. Actually plotting by hand works very well but is extremely time consuming. I have done the plotting by hand many years ago and have spoken to photographer's who have done it by hand.

I try to keep the proccessing time as reasonable, especially if you are processing film in BTZS tubes to 6 minutes. Processineg film past 16 minutes gets quite tedious. There is an article in the D-Max Newsletters where Phil increased dilutions of the developer and processed film out to about 64 minutes in the BTZS tubes.

Fred