adjusting proccess times with ISO manipulation

How do you adjust the processing time after changing the ISO from 400

to 16,000 and if you could give me a summary of how you calculate the

proccessing time so that i can do it for myself next time. thank you

very much

Unfortunately I don't know much about darkroom work. But 5 1/3 stops? What film are you using? I'd be interested to see the results, if you can post them.

ISO defines the contrast of the film; in the Iso definition; thus a given film and developer ususally has but one iso rating...

16,000? that's more than a 5 stop push. Are you sure you don't mean 1600 which is only a 2 stop push? The times are going to be different depending on the chemistry you're using. A regular processing time is going to be about 3mins. The documents that come with your chemistry usually tell you how much to extend development for push processing. I guess you'll just have to interpolate for a 5 stop push. It's not very common.

You can expose many b&w films within a wide range of exposure indices (EI). While the "normal" EI for a given film may happen to correspond with the ISO, it doesn't always happen. Even if it did you might not want to use the same developer and technique the manufacturer used to determine the ISO.

 

Okay, enough semantics. You probably want some practical applications.

 

When I push film (a bad habit of mine) I first check the available data. There's lots of data for most 400 films pushed to 1600. From there you're pretty much on your own and must draw from the existing data, take some leaps of faith and conduct lots of tests.

 

A few tips...

 

Buy a bulk roll of an appropriately pushable film or buy enough factory short loads (24 exposure) to get a discount. With bulk loading I generally load up 12-exp rolls for experiments. I find Tri-X (TX) and T-Max 400 (TMY) very pushable so those are good choices for buying in bulk.

 

Don't experiment with important photos. IOW, don't go out and shoot an important session at, say, EI 6400 for the first time and expect to get it right. Instead, experiment using easily repeatable circumstances. I have a couple of fairly standard still life setups under halogen and tungsten light. I also just walk outside and shoot some familiar stuff around the house and lakefront, day and night. This way I'm not constantly wondering whether it was the light that was the problem.

 

Pick one or two developers at most and experiment with them to exhaustion for several months (unless you have time for full time experimentation, in which case the trials can be done within a few weeks).

 

I'd suggest starting with something like TMY and Microphen. I routinely use this combination at EI 1600 for day and night shooting on the same rolls. It shows promise of being able to handle EI 3200, tho' so far I haven't found many situations where I needed to push that far.

 

I also like Tri-X in Diafine but this is a fixed speed developer, around EI 1000-1600. Unlike conventional developers you can't extend the effective "speed" of Diafine with longer processing.

 

Anyway, I can tell you what works for me using my materials and techniques. But I'm still gathering data and don't have much concrete info to share other than what's already in my photo.net folders.

 

Hard push processing, like you're talking about, can be done and has been done but there's surprisingly little hard data available. I suspect this is in part due to the inevitable arguments the subject engenders, especially from zonies.

 

Suffice it to say, with push processing I choose to distinguish between *effective* speed and *true* speed. The latter deals with maximum shadow detail and is a topic for zonies and densitometrists. The former is more subjective. For example, if I get a hint of Zone III from an ISO 400 film pushed to 1600 I'm very pleased. And what I really strive for is good gradation in the midtones without blocked up highlights - that's what I mean by effective speed. It's within the reach of most fast films using most developers.

 

So, you're pretty much on your own here. BTW, you might consider using Delta 3200 or TMZ for pushing to EI 16,000 - that's asking a heckuva lot from any 400 film.