Question about testing for film speed...

[Christopher Barrett]

The tutorials I've read about shooting ISO test generally involve metering a grey card, then placing it in Zone I for an exposure and Zone VIII for another, then doing this again at different ISOs.

I was wondering... couldn't I just place a light at a sharp angle to a wall to create a 10 stop gradation and shoot that? It seems that it could produce a less confusing workflow. I could tape meter readings to the wall to define the Zones.

Thoughts?

Thanks!
CB

[xkaes]

Hello,

Kodak, Stouffers and others make positive and negative step scales to try to shorten the number of tests you need to perform to determine the correct exposure or development "under study". Ask 10 photographers your question and you will get 20 answers. It's important to understand that:



The best book I have ever read on this -- and similar questions -- is "Controls in Black and White Photography, by Richard Henry (there are at least two editions). He basically says "Don't listen to anyone; do your own experiments" -- but he tells you how to do them and why. In short what works for one photographer will not apply to another for a number of reasons.

In my opinion, you need to start at the end and work backwards:

First, pick your paper and figure out what is the best development for it. Then determine the best exposure for the paper -- with YOUR gear. Then you are ready to figure out what the best development is for your film and your development. Only then are you best suited to determine the best exposure for your film. Check out:

http://www.subclub.org/darkroom/henry1.htm

[Neal Chaves]

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). 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. 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.

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 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 expensions, 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 failure 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 out to one minute.

[Kirk Gittings]

Chris I know you like precision in all things. FWIW (this is probably NOT precise enough for you) film speed for me is related solely to generating adequate shadow detail (Zone IIi placement of important shadow detail). I'm not concerned with "speed"as it relates to being able to use a faster shutter speeds or smaller apertures. That "ASA" and placement will render sufficient shadow detail for a given method(s) of output. I would much rather have too much and print the shadows down than have too little and try and extract detail that isn't there. Shadows that are printed down have a luxurious depth to them. As such, a long time ago after a lot of testing, I started rating everything at half the box speed. It works for me and makes for less testing which I don't enjoy all that much.

[ic-racer]

Any uniform target that is not colored. A colored target will alter your results. A gray, white or black card will work.

[Christopher Barrett]

Ha... Kirk, for some odd reason, I really enjoy this process.

[John Olsen]

Interesting thoughts about speeds and testing, but please tell us whether your recommendations are for a digital scan-and-print or for an enlarger output. Drum processing or tray? There seems to be lots of variables that make comparisons difficult to understand. A little more background information may help determine which schemes go with which workflows. But nevertheless, thanks for sharing.

[Bernard_L]

I would much rather have too much and print the shadows down than have too little and try and extract detail that isn't there.

100% agreed. Which leaves the question of negative contrast. It seems that the manufacturer recommended contrast index (for enlargements, not contact) has been generally going down from 0.65 to 0.55. I'd like to hear from experienced practitioners what is their target value for, say, an enlarger with opal bulb and condenser, and "normal" scene. Related question: is that decrease in target CI possibly related to more people scanning rather than wet printing?

[Doremus Scudder]

Christopher,

First, it has been fairly well shown (and I'm now convinced) that film-speed testing is largely superfluous. If you're using the Zone System, just rate your film 2/3-stop slower than box speed as a starting point and go directly from there to determining developing time. You can always adjust later.

If you insist on determining a personal EI, your results will vary depending on the methodology you use. The Zone System speed point of 0.1 over B+F is not the only way to find film speed (and not the one used for determining ISO). Stephen Benskin has posted copiously on this either here or on APUG. If you're interested, you might want to search on his posts and do a bit of research. Be prepared to read a lot.

Might I suggest a less-quantifiable, visual approach to determining EI and film development time. I learned this years ago from Minor White, et al. in the book "The New Zone System Manual" and have modified it a bit for my own purposes. The basis for all testing is a "proper proof" made on the enlarging paper you plan to use (most). A negative is printed to find the minimum exposure needed to render the B+F density equal to maximum paper black. The trick is in determining this exposure, since viewing light plays an important role here.

The starting point is a negative you have made of a real-world scene that you have carefully chosen and metered so that you know where everything was placed and fell. Keeping good notes here is essential. You likely already have such a negative.

The original advice was to contact print negatives for the "proper proof," but I have moved to enlarging then negative to a magnification equal to my most-used enlargement. I place the neg in the carrier leaving a stripe of nothing on one edge so the paper will see the raw enlarger light there. I then make a test strip with a clear negative (or the rebate) that includes the empty stripe and the edge of the negative so I can compare the area exposed through the negative to the area exposed directly to the enlarger light.

I develop and dry (important) the test strip and evaluate it under what I consider to be ideal display lighting and find the exposure where the black of the unexposed rebate merges with the max paper black next to it. Use too bright a light (e.g., direct sunlight) and your EI will be way too slow and vice-versa.

Once you have that exposure time (light-source intensity needs to always be the same, so head height, filtration, etc. all need to be the same), then simply make a straight print of your negative on the same paper/grade as your test strip, develop it for the same time as your test strip and dry it down.

Compare the print with your notes and adjust EI and development accordingly as needed. Shadow detail not where you want it? Adjust the EI. Highlights not where you want them? Adjust the development time. Do this a few times and you'll have a pretty good baseline for "Normal." Now do the same for expansions and contractions.

I feel that using a real-world subject together with the meter and lens(es) I use gives better results than other methods. It takes into account the actual flare of the system and my metering techniques. Similarly, making the proof with an enlarged negative takes the flare of the enlarging system/lens into account. I find this gives more honest, practical data than using step wedges or metering a uniformly-colored surface (too white and you'll have more flare than you usually have, yielding a false EI and vice-versa).

This method works especially well for negatives developed in staining developers where a densitometer may give erroneous readings due to the color and function of the stain.

I keep good notes and make tweaks to my development times as needed.

Best,

Doremus

[xkaes]

Like, I said, "Ask 10 photographers, and you will get 20 answers!"

They are ALL right -- for them, and ALL wrong -- for you.