Film testing: FP4+, D76, in a Jobo

I am conducting some experiments on Ilford’s FP4+ film using Kodak D76 developer. My testing is as controlled as I can make it using a Stoffer’s step tablet negative, Jobo rotary processor and keeping all the temperatures and processing variables as consistent as possible.

I’m using an Xrite 810 densitometer with a new bulb and calibrated with a new calibration strip from the manufacturer.

All my testing has been by sandwiching a 4x5 sheet of film with the step tablet and exposing it on a white wall illuminated by a blue photo bulb taking care for even illumination. Here’s what I’ve gotten so far:

My “normal” ISO rating for this film should be approximately 80.

________ISO_____DT______DR____________ER_________gamma
N-2_____40______6.5_____3______________5__________0.061
N-1.1___64______8_______3.9____________5___________0.078
N_______80_____10_______5_____________5___________0.100
N+.5____100____13_______5.4____________5___________0.110
N+.7____125____18_______5.7____________5___________0.114

DT = Development Time in Minutes
DR = Negative Density Range in stops
ER = Egative Exposure Range in stops

Assigning N as the process that gives me 5 stops of density for 5 stops of exposure, N-1 and N-2 worked out about as I expected.

The plus values though are a little troubling since gamma flattens out pretty quickly after about 13 minutes of development. I couldn’t even reach N+1 at 18 minutes of development as you can see the change of my curves slope (gamma) from 13 to 18 minutes was very small. I attached my gamma curve below. Plotting this data in a spread sheet and creating a polynomial trend line (dashed) yielded an extremely good fit. The gamma curve seems correct.

Has anybody done any testing with FP4+, D76, in a Jobo? I’m interested in comparing your data results with mine.

Thanks,
Bill

PS: sorry for the funny table above; I couldn't figure out any other way to make it look reasonable in this posting.

Sure your gammas aren't off a decimal place? Raise them one order of magnitude and you'll get "normal" gamma with a development time of around 6.5 minutes and reach N+1 and N+2 easily. I haven't used the combo you're testing, but it would appear to be about right. You'd have to go to shorter times for N-1, N-2. Something is off with your numbers if that's not the case.

Lee

Lee L said:

Sure your gammas aren't off a decimal place? Raise them one order of magnitude and you'll get "normal" gamma with a development time of around 6.5 minutes and reach N+1 and N+2 easily. I haven't used the combo you're testing, but it would appear to be about right. You'd have to go to shorter times for N-1, N-2. Something is off with your numbers if that's not the case.

Lee

Click to expand...

Thanks for the tip Lee... I'll dive back into my spreadsheet and take a look...

Bill