testing for film speed (again)

[quigon]

Hi, I know the topic has been discussed before and I have studied lots of posts (and books). Anyway as I've always been a slow learner I have some doubts.

I want to test Fomapan 100 in Rodinal 1+50 because I've experienced that my best results are when I expose at 32 ISO (!!!)
So one film, one developer at one dilution.
Stouffer step wedge 4x5 21 uncalibrated, sandwiched with a sheet of Fomapan 100. The light of the enlarger as light source: no lens, but sinar shutter mounted on the enlarger. Shutter speed @1/4.

The question: How do I calculate an exposure for zone X for the fomapan 100 exposed for the box speed (100 ISO) in the above illustrated scenario?
Reading with a spotmeter on the base of the enlarger? Ok, but which EV should I obtain? 10? 11? (remember there is no lens)

I thought that if the film were honestly rated by the manufacturer, exposing the step wedge+ film for 10 zones I should get a density (over b+f) of 0.1 log in sector 19 of the developed film. That would mean 100 ISO. 0.1 log in sector 17 would mean 50 ISO, and so on.

Please tell me where are the flaws in what I think to do.
Thanks Luigi

[lantau]

I'd remove the lens, take an incident reading in its place. Then place back the lens and set aperture and shutter speed according to the reading.

[Michael R]

A few comments:

1. The exposure index that consistently gives you the best negatives (ie what you have determined is best for printing/scanning through practice) is what matters

2. An ISO 100 film will, by definition, have a Zone System speed of 64. Use that as a rough guideline to compare your results with.

Using an enlarger is not the easiest way to do a Zone System speed test, but it can be done. Do you have access to an incident exposure meter? If not, you can make approximate measurements with a spot meter using a few assumptions and/or applying a few formulas.

[Peter De Smidt]

I prefer to use a method as close to general photographing conditions as practical. An enlarger light source is quite different than the sun.....But.....Haven't you already found your exposure index, i.e. EI32? That's seems like an appropriate value to me for Fomapan 100 in Rodinal.

Your meter will give you a reading that will give whatever tone it's pointed at a Zone V density on your negative if you have the right EI and development time.

Assuming your EI and development time/temp/agitation are correct, meter a low scene density (usually a shadowed area) where you'd like detail. Suppose that indicates F/22 at 1/25th of a second for Zone V. You now want to close down 2 stops to place that value on Zone III, which is the standard place for detailed low values. That would give f/22 at 1/1ooth of a second.

Now spot meter the brightest area of the scene where you want detail. Suppose it gives f/22 at 1/800th of a second, a 5 stop spread (i.e. zone III to zone VIII). That's perfect for a standard development. If it's less, you might want to develop 15% more than normal (or so). If it's more.....honestly, don't worry about it. Film has a tremendous range.

[ic-racer]

Rather than the 'standard candle' that used to be used, I use a 'standard film' for calibration. This is a valid test and has been described in various papers.

For example I use Delta 100 or Tmax 400 and compare my other films to that to find their speed. https://www.largeformatphotography.i...light=shanghai

Produces a sensitometer calibration package consisting of two rolls of film of the same emulsion. The CCF must expose one roll with a calibrated step-tablet exposure and age the film to reduce latent image effects. The second roll must remain unexposed. The CCF also stores the sensitom- eter calibration package under controlled conditions at all times, and keeps appropriate records for periodic verification.

AIR FORCE INSTRUCTION 14-202 28 MARCH 1994
Intelligence

[quigon]

Thanks everybody for your help. I have indeed used the method in AA the Negative first thing, and I got and EI of 40 ISO, I also tried BTZS method (after having read the book) but the result was disappointing: 160 ISO (which is impossible: the negative and prints were really with no detail in the shadow areas). At last I tried the method "Use your eyes" which Paul Wainwright published on his website: 25 ISO. As I wrote in my first post I have seen that a EI of 32 ISO is what I like most. It was my intention to use a way of testing avoiding (as far as possible) the problems connected to lenses, and that was -- at least -- repeatable.
I'll stick to 32 ISO for now.
Thanks again
Luigi

[willwilson]

Hi Luigi,

I just got done dusting off a page on my website about film dev testing. It is a method I use with a densitometer that works pretty well. It is based on an article written by Gerry Russell that was in view camera. I turned the method in the article in to a spreadsheet you can download and use which makes it pretty easy.

https://willwilson.com/Film_Developm...sitometer.html

Black and white film is so flexible honestly as long as you don't under-expose you are probably good. An over exposure of even 2-3 stops is also almost always fine for me and remains very printable. There is something to be said about the perfect negative. Having a great neg makes the work in the darkroom much more enjoyable. My personal opinion is that nothing important should be in the 0 - .2 FB+F range of a negative (which is zone I and zone II traditionally). I always meter my critical shadows, that will print down to zone I or zone II, up and in zone III on the negative, so a .35-.6 density. This allows for less errors and less exposure thinking in the field.

[Neal Chaves]

I have posted this many times in answer to the finding film speed question. No one has ever questioned the accuracy of this method, which Mortensen open sourced in the 1940s.

Years ago I learned an excellent method to find the correct developing time and EI for any film. I source was an article by William Mortensen. Mortensen wrote some excellent books and articles about basic sensitometry. The last time I did this test was when I abandoned Tri-X and switched to HP5+ due to cost about five years ago. I proceed as follows.

I set up my trays with my favorite developer HC110B (1:31), now Ilfotec HC (1:31). I pull out a sheet from the package in the dark. and then when the package is sealed again I turn on the room lights. This part of the test is done under the lights. I cut the sheet into five strips and mark them 1-5 by punching holes with a paper punch. Lets say the recommended time is 5:00. I want to see 3:00, 4:00, 5:00, 6:00 and 7:00, so I throw all the strips into the developer and agitate as usual until 3:00 when I move the No.1 strip over to the stop bath. Then I pull No.2 at 4:00, No.3 at 5:00, etc. I fix, wash and dry the strips as usual. What we are looking for is the best usable film DMax value. Obviously the film has been fully exposed! When strips dry lay down a page of news print on a table in good light. Find the strip through which the news print is barely visible. That's your developing time. Now to find the film speed.

Go outside in unchanging light conditions and expose five sheets and expose one at the manufacturers rating and then the other four at one half a stop and one stop less and one half a stop and one stop more. In the dark, develop them all together for your newly derived time. Contact print them together exposing and developing the paper for maximum usable paper DMax value through the film base plus fog negative rebate area. Pick out the best-looking contact print and you have your film speed.

Because my 7:00 negative looked the best on the first test, I did the test again with 7:00 as the central developing time and found that 8:00 was indeed too dense. This HP5+ time was the same as the as the developing time I had been using for Tri-X and film speed was also the same, EI400. I have also switched to Ilfotec HC developer due to cost and availability and find it to be a clone of HC110.

Many of the last generation of B&W gurus favored a development time of 5:00 for Tri-X and suggested an EI of 64-100. You can do the above test backwards, developing for 5:00 minutes and finding the film speed. I like 100. The difference between negatives exposed at 100 and developed for 5:00 and those exposed at 400 and developed for 7:00 is quite subtle. Both could be considered "normal" or N negatives. The 100 negative has slightly greater shadow and highlight detail that only a careful, knowledgeable viewer could detect. This slight improvement might not be worthwhile trading for two stops in the field. I do routinely rate HP5+ at 100 under powerful strobe light in the studio and it produces beautiful skin tones.

From here, if you are still with me, you can derive expansion and contraction schemes for both the 100 and 400 "normal negs". I do this by changing dilution rather than time. Make sure you have at least 1 oz. of the concentrated sauce for each 8X10 sheet or equivalent. For contractions I found that 3/4 oz. concentrate to 31 1/4 ozs. H20 yields an N-1 neg at a one stop loss in film speed and 1/2 oz. concentrate to 31 1/2 ozs. H20 yields an N-2 neg at a two stop loss in film speed. For expansions, 1 1/4 oz. of concentrate to 30 3/4 ozs. H20 yields an N+1 neg at a one stop gain in speed and 1 1/2 ozs. concentrate to 30 1/2 ozs. H20 produces an N+2 negative with a two stop gain in speed.

If you look at the chart of Tri-X film speed in Phil Davis' BTZS book you can easily pick out the film speed in HC110B 5:00 as EI 64.

Don't apply reciprocity exposure and development corrections for long exposures (1/2 sec. +) based on published data. Test for yourself and you may be surprised. I wasted a lot of time and effort producing long exposure negatives that were thick and flat. When I finally tested, I found no compensation was required for TXP or now HP5+ out to one minute.

[Peter De Smidt]

I prefer 1/3rd stop increments to 1/2.

[Neal Chaves]

I prefer 1/3rd stop increments to 1/2.

It's most important you are actually in the ball park. Most players are happy just to hit a home run, masterful hitters like the Babe can point where the ball will go.

In the early 1970s, when I gave a Navy photographer his personal EI (exposure index) for Tri-X and developed his film for him, he exclaimed profanely that the negatives were "bullet proof" but admitted "They made nice prints though, damn nice prints." on a normal grade of paper. Yet he could never bring himself to do the same and continued to use the data published by the "Great Yellow Farter", that required grade 4 paper and much manipulation to produce prints I would still find unacceptable.