Film Speed and Developing Time

[Flexnib]

Hello All,
I am trying to use the article in View Camera magazine by Steve Simmons to help find my personal EI. I understand the closing down 4 stops, but am having trouble with the next steps.
What would be "at a film speed of 75%" Would this mean changing the asa on my spot meter from 320 to 240asa then metering the wall again and close down lens again 4 stops?
50% asa 160
125% asa 400
150% asa 480
please help!
Arthur, NYC

[IanG]

Once you've determined your speed as 75%, assuming your shooting the Tri-X 320 you just set your meter to 240 EI. It's a simple as that, then use your meter as normal.

Ian

[Ken Lee]

Developing times may vary from person to person, but after all the testing has come and gone, most people shoot most b&w films at 1/2 the stated ISO.

This is more than a coincidence. It's probably due to the way that manufacturers determine their ISO or market their products.

[Bruce Barlow]

Sorry, Ken, but while "most people" use 1/2, that doesn't mean it's best. My tested Tri-X speed for LF and 35mm is 400, and I choose to goose it a little and use 320. That's good: I want as much speed in LF as I can get for the subject matter I typically hunt.

They're simple tests, whose psychological value (confidence in the materials) is well worth the effort. Exposure and development are mechanical, and should occupy as little of our brains as possible while guaranteeing good results.

[Flexnib]

Thanks, but will someone please answer the question asked?? I am trying to find out what my speed will be.

[IanG]

Once you've determined your speed as 75%, assuming your shooting the Tri-X 320 you just set your meter to 240 EI.
Ian

I thought that was the answer

240 EI - ASA

Ian

[Flexnib]

This may be the answer but since I do not know my EI. I am asking in the question above if this is how I should be doing the test to figure my EI out.

[IanG]

OK, sorry I thought Steve's article was quite good and explained it well, it's roughly how I did my Zone system speed tests about 20 years ago.

Maybe someone can post a link to a better explanation. Unfortunately it's not clear quite what you've done so far, so where your stuck.

Ian

[Steve Barber]

If I understand your question, you are trying to find a film speed for a Zone I density based on meter reading which gives a Zone V density. That is the reason for the four stop reduction. So, using the film's rated ASA, reduce the aperture 4 full stops. This gives you your initial setting for the first exposure. Then, open the aperture 1/3 stop for each exposure thereafter. This will start you with what would be a Zone I exposure at the rated ASA for the first one and an increase in the exposure for each succeeding one that will correspond to a decrease in the film rating of 1/3 stop for each one. A total of six will take you from an ASA of 400 to an ASA of 100, which should be enough. Start with a large enough aperture so you don't have to worry about reciprocity and remember to keep the camera focused at infinity so you don't have a bellows factor multiple to contend with. When developed, one negative should give the density you are looking for and that will indicate the film speed to use for that combination of film and equipment you used to make the exposure.

[Steve Barber]

Yes, I forgot you were starting with 320 not 400 film. If you are using 320 (TXP), use 400 anyway. It does not hurt to start a little high and it might help. Just ignore where I said "using the film's rated ASA" and use 400. If I am wrong and you are using something else, the idea is the same, just adjust the rating accordingly.