how to do the math for speed film test

I am testing a film for personal film speed. Thanks to one of our forum members I have a method to follow. Since I am really bad at math and find formulas difficult, I wanted to ask how to interpret my results.

The formula I followed said the take a reading of a grey card, filling the entire unfocused ground glass with the blurry grey image. Then I took a spot meter reading with a Pentax V and it gave an exposure of f 11 at 1/60 second. The instructions said to stop down the aperture to 45. That theoretically would be zone one.

Then I took five shots, each at about 1/3 stop greater than the previous. I made a exposure test strip from a developed unexposed negative to get base plus fog. Then after developing and printing under controlled conditions I should find the first negative/print that varied from maximum black. That print would indicate my proper zone 1 for my film.

Is this correct so far?

I have done all that and found that having started with f 45 at 1/60 second, the first print that showed a difference was shot at f 18 at 1/60 second.

So, seeing those figures, how do I determine what the true proper speed for my set up? The film I am using is Arista EDU Ultra 200 box speed.

Thanks so much. A greatly challenged math student.

You seem to have found a speed of 32.

I think we'll need to know more about your method because this doesn't seem right.

Yeah, it seems odd to me too. Perhaps I need to do the test again and make sure I have done everything exactly correctly.

There's a lot of "slop" in this kind of test - mostly at the printing stage where it is very hard to judge the shortest time to max black, and then visually judge the next lightest tone (you're better off printing to a middle grey tone and then looking for a tone slightly lighter). That being said, some quick things to check for as I read your post:

1. When you do the camera part (filling the ground glass view with an unfocused image of the grey card), make sure the camera is focused to infinity for the lens used

2. Assuming you started at f/45 and then took an additional 5 shots in 1/3 stop increments, I think you only get down to about f/25. Here's a f-stop sequence in 1/3 stops: 45, 40, 36, 32, 29, 25

The instructions I followed were on Barry Thornton's web site. I agree that there are some possibilities for sloppiness on my part. There is another test included in the Way Beyond Monochrome book that I think I will try. In that book there are three methods he recommends, a super easy one, one a bit more complicated and a final, really thorough test with a density meter, which I don't have. Perhaps the middle txt would be sufficient?

Put the negatives over you meter. Look for the negative that drops the meter reading by 1/3 stop over base. That is your 0.1 log d zone one.

Oh, you might not have developed for enough time to get the full speed of the film.

I've got lots of ideas how you can tell if you developed long enough.

When you photograph the gray card, you first must have your camera focused at infinity. Then fill the ground glass with the gray card. If you merely de-focus the camera, you've changed the focal length and the proper exposure.

In addition the the grey card, you also need to see what is happening to the extremes... For the highlight test, put a white sheet with a yellow post-em note next to the grey card... The white should be close to D-max with the density just enough to barely see through it, and the post-em note should just separate into another step if exposed/developed correctly...

For a D-76 type developer/normal exposed film in daylight, expect a range something like this:

If you spotmeter a scene in sunlight, place a bright white object (you want to hold detail in) and meter that... One stop under that reading should be middle grey, and two stops under that will be the safe shadow region that will hold detail well, but the 3rd stop under middle grey will record form, but no detail... Under that will be no exposure... This is about the range for a standard developer + film... If you meter for these, you will safely be within range...

For the developing, just long enough before the D-max blocks up... This is the simplest "zone" type system you can use for normal (N) negs, and will allow you to fit the range of exposure onto most films (with standard film developers), and print easily, before other processes/steps are tried... And will work with the vast majority of normal scenes you will encounter...

Good Luck!!!!

Steve K

I truly appreciate all your great answers and advice. However, my brain doesn't think in an analytical manner and all the information is confusing to me. In the end, I suppose I just need a simple yet clear method for determining my film speed. I know there are endless variables, but I can't process all that at my present stage of learning. All of you are far advanced in this process and I am just a newbie at the technical side of things.

Does anyone have a very simple and clear method for getting film speed? Then perhaps I can experiment and start thinking about the variables. Thank you so much!

Alexis

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Originally Posted by Peter Gomena

When you photograph the gray card, you first must have your camera focused at infinity. Then fill the ground glass with the gray card. If you merely de-focus the camera, you've changed the focal length and the proper exposure.

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So on a 4x5 view camera that means extending the bellows all the way to it's maximum?

Just go with the (ISO) speed on the box first, and see if it fits in with what I posted before... Remember, the developing time controls the highlights, but the exposure will control the shadow level... Read what I posted again carefully... ;-)

This will get the proper exposure level on the film... Then comes the developing tests... Later you can try overexposing the film slightly (+ 1/3 to 1/2 stop, and slightly underdeveloping the film to find a "sweet spot" for nice highlights/shadows...

Steve K

OK, thanks Steve, but as you will soon discover I am as dense as some negatives:) So let me clarify a bit. I should still do the grey card test, right? Then I should do another test with a grey card, a white sheet and a post it note n the scene, right? That should likewise be focused at infinity, or should it be focused normally? Do I do this highlight test after I have completed the grey card test to determine speed? Should it be shot at the newly determined speed test, or do I shoot several shots at varying apertures 1/3 stop apart?

I'm sorry that I don't completely understand.

I need a cheat sheet that lists all the steps I need to take. Does that exist somewhere?

Thanks again,

Alexis

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Originally Posted by LabRat

In addition the the grey card, you also need to see what is happening to the extremes... For the highlight test, put a white sheet with a yellow post-em note next to the grey card... The white should be close to D-max with the density just enough to barely see through it, and the post-em note should just separate into another step if exposed/developed correctly...

For a D-76 type developer/normal exposed film in daylight, expect a range something like this:

If you spotmeter a scene in sunlight, place a bright white object (you want to hold detail in) and meter that... One stop under that reading should be middle grey, and two stops under that will be the safe shadow region that will hold detail well, but the 3rd stop under middle grey will record form, but no detail... Under that will be no exposure... This is about the range for a standard developer + film... If you meter for these, you will safely be within range...

For the developing, just long enough before the D-max blocks up... This is the simplest "zone" type system you can use for normal (N) negs, and will allow you to fit the range of exposure onto most films (with standard film developers), and print easily, before other processes/steps are tried... And will work with the vast majority of normal scenes you will encounter...

Good Luck!!!!

Steve K

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Yes, the reason to focus for infinity (or at least > 6 or 8 ft), is so that there is no bellows factors that will influence the exposure... Yes, you can include the white sheet with the grey card exposure, but you would need the grey card exposure for the print calibration step where you would be matching the grey card to the print grey patch... But for film, the white/yellow step is important for exposure as overexposure would make this step invisible... The next test would be to shoot a daylight scene with highlights you want to hold detail in, to shadows you want to keep... (Use the measuring scale I mentioned in other post...) If your highlights are too dense, it might be overdeveloped, or you would have to underexpose, but use the posted info to tell the difference... (If you can see the wh/yel step and see through the dense part of the neg slightly, you are there... Then look at the shadows on the neg and see if they fit within what I posted when metering...

This should get you started...

Steve K

As a question, how do you know that the 1/60th film speed that you used is accurate? I bought a shutter speed tester from Calumet decades ago. I find the actual shutter speed at a setting and use that value on my meter.

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Originally Posted by LabRat

In addition the the grey card, you also need to see what is happening to the extremes... For the highlight test, put a white sheet with a yellow post-em note next to the grey card...

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Alexis, Please be aware that this is not part of finding personal film speed.

What kind of person are you? Do you enjoy testing things or do you enjoy taking photographs and making prints? I do not mean to pejoratively imply that a desire to test things is lesser than, or opposed to, a desire to make photographs/prints - I do both and I do own a densitometer that I use on a regular basis. However, if you do not enjoy the idea of testing things, I would venture that you might be better off finding a simpler method of establishing your own exposure/development regimen.

The basic idea here is that you are trying to control the characteristic curve/H-D curve/transfer function - think of this as the rule that governs how a brightness/luminance value out there in the world is changed to density values on the print. Now there are actually two stages with B&W film - so there are two transfer functions you need to get to grips - one which translates luminance values in the world into a density on the negative and one that governs how a negative density (actually the luminance of a printing light that has been changed by a negative density but we assume that the intensity of the printing light does not change) translates into a print density. The basic principle here is that exposure mainly affects the shadows and development mainly affects the highlights. Paper is usually developed to completion and so we try to do whatever adjustments we can at the negative exposure/development stage.

As you can imagine, there are dozens of ways of varying accuracy/ease to get these down. The big problem is that we need to know what a properly exposed negative should look like and what a properly developed negative looks like, the problem being that we don't know what these look like. Experienced workers know what these look like and can usually home into very reasonable solutions for new material within a few exposures. If you don't know what to look for, some lab learning can help but so can some field learning. Like all learning, it tends to be initially difficult - and the point to keep in mind is that lab learning is a different process from field learning.

At one end, you could approach this very technically. You could start by exposing a piece of your photo paper to a step wedge in your enlarger/whatever your print making process entails (for e.g., if you are working in 4x5, Stouffer makes 4x5 step wedges that fit into enlarger stages). The step wedge has bars of various densities, usually varying in 1/2 stop or 1/3 stop values (0.15 or 0.1 density units - density values of 0.3 correspond to 1 stop i.e., a density of 0.3 units more will allow half the light to pass through). Adjust exposure till you get a range from black to unexposed paper base white (usually you will look for an exposure that gives you a series of bars of white at one end and a series of bars of black at the other end. Look for the first off-white and the first black bar and count up the number of bars in between, multiply by the step wedge factor (i.e., 0.15 or 0.1 density units). That is the negative density range your paper wants to see to give you a full range from the best white to the best black the paper is capable of giving. In other words, this is telling you how long you should develop the negative. Next expose some film in a manner similar to what you have done. Develop for the recommended time with fresh developer. Measure these densities with a densitometer or compare then visually with the step wedge to assess the density - your eye is actually very good at comparing densities. Many of the negatives will be underexposed i.e., the film did not receive enough exposure and so the development does not produce any density beyond that contributed by the film base and general fog (often abbreviated to fb+f). The first value that shows you an increase in density is your film speed. The next stage can involve sandwiching the step wedge to your negative and making an exposure (actually expose a bunch of film this way - this can be done under an enlarger). Now develop these for different times. From your paper tests, you found the density range your paper wants to see. Find the development time that gives you what you need.

Needless to say, many find this kind of testing regimen stifling. And with good reason. If you want to get on with the making of photographs and prints, this kind of testing can be trying to the soul. It is like learning equations within a stuffy classroom while you want to be out in the real world digging up fossils of dinosaurs.

So, at the other extreme, you have systems that do not break down things into the individual components. Instead, you go out into the world and dig up fossils and try to learn on the job - just relax and accept the fact that sometimes, there will be screw ups. Screw ups happen in the lab too - its just that they happen in a controlled situation with little to lose. The usual advice that is given is to start with about half the ISO stated on the box and about 2/3 the recommended development time. Then make photographs and print them - lots of them. Sit down with the prints and the negatives and look at the shadow regions. If you consistently find that your shadows do not have enough detail, drop your film speed some more. If not, try increasing film speed in 1/3 stop values till you get to that point where your shadows do not have enough detail. People usually recommend some margin here and to give somewhat more exposure than this point. This is your film speed. Now use this film speed and make some more photographs and print them. If your highlights are always washed out/difficult to print/require lots of dodging and burning, reduce development time. If your highlights are consistently flat and grey/muddy, increase development time. So, this is a trial and error way to find out what a properly exposed and developed negative should look like and you can expect to lose some pictures along the way. Some of us are comfortable with that, some of us are not. Those of us who are not tend to pooh-pooh this approach but it is actually surprisingly good. And it is what you will use constantly because you will unconsciously be doing something like this kind of assessment with each subsequent negative you make and that provides a constant feedback cycle to help you keep your process under control - a bit like tasting the dish as you cook it, except the dish here is not an individual picture but a process.

As someone who owns a densitometer and uses it on a regular basis, I will argue that you should not underestimate the utility of the second approach. There is a fair bit of margin in this system. For e.g., consider that many will establish a film speed with step wedges and densitometers and then put in a margin and overexpose slightly. This actually makes sense since slight overexposure is preferable to underexposure but it highlights the issue that we are not aiming for some scientific level of precision but are trying to establish the useful boundaries for our work to ensure we stay within those boundaries or are at least aware of when we are sailing too close to the edge of the world....

I enjoy making photographs and printing and use something very much like the second method in practical terms. But I do enjoy also learning about and testing photographic materials and over a large amount of time, that learning and information becomes second nature. More importantly, the two ways of work actually inform each other and become a creative tool in their own way. Your testing might give you ideas about photographs you could try to make and the photographs you make will start to give you ideas about different kinds of controls that might be worth testing. I think the important thing is to make sure you are enjoying yourself at some level - that's what keeps you at the game.

Cheers, DJ

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Originally Posted by neil poulsen

Alexis, Please be aware that this is not part of finding personal film speed.

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But it should be done prior to the testing; using an inaccurate shutter speed in the testing is a waste of time/film/chemicals. I made my own shutter speed tester and have checked all my shutters at all settings, then taped the results on my lens boards so I can make the necessary corrections in the field.

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Originally Posted by ic-racer

Put the negatives over you meter. Look for the negative that drops the meter reading by 1/3 stop over base. That is your 0.1 log d zone one.

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The math to find ISO is not difficult if you know the intensity of your sensitometer and your step wedge densities. (Speed = (0.8 / Hm))
However, when doing your exposure index, no math is needed. Just look back at your notes to see the ISO to which your meter was set when it exposed the 0.1 log d negative.

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Originally Posted by Jerry Bodine

But it should be done prior to the testing; using an inaccurate shutter speed in the testing is a waste of time/film/chemicals. I made my own shutter speed tester and have checked all my shutters at all settings, then taped the results on my lens boards so I can make the necessary corrections in the field.

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IMHO, that is the most important point made so far. I've written this before: large format shutters in general are highly susceptible to inaccuracies. Some of us find the speeds that actually correspond to a standard and work from there. For example, the only shutter speed I can always trust is B (or T). If we are lucky we might fine other speeds that correspond with our other lenses. By chance, I find 1/60th more consistent among the lot. Your experience is likely to vary. It is a crap shoot.

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Originally Posted by fralexis

So on a 4x5 view camera that means extending the bellows all the way to it's maximum?

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No the exact opposite is what they mean... to focus at infinity, you aim at a distant object. You will find the 4x5 view camera bellows is closed up most of the way when you are at the right focus position for a speed test.

Then without changing the focus position, fill the ground glass with the blurry test target.

If you did it the other way, and you stretched out the bellows... that could explain why your test seems to indicate 32 speed.

--- There isn't one cheat sheet reference for film speed testing because everyone does it differently and everyone has their own write-up they like ---

I have my own ideas too, but I don't want to make things complicated for you right now.

If the bellows extension was your problem, you might test again focused at infinity.

Otherwise, you could do no harm shooting a 200 speed film at 32. I once had a test problem and found 64 speed for a 400 speed film. I went around for a year shooting that film at 64 and got some of the best pictures of my life.

Many years ago I got ahold of some medical imaging film, EktascaB. We used it at work to image CRT traces . To use it in an 8x10 camera at home I loaded a few film holders and did some test shots of the swing set in our back yard.

I figured it was pretty fast to capture fleeting spots on a CRT. I set up a series of exposures by choosing a shutter speed and aperature correct for the lighting assuming a film speed of 50 and pulled the slide for one exposure. Then inserted the slide 1/3 in and made the same exposure. Next the slide was pushed in to the 2/4 position (about) and another exposure was made at half the first shutter speed.

The one sheet of film had been exposed at an assumed ISO 50, 100 and 200. Iflipped the film holder did did the same at 200, 400 and 800. When the film was developed, it seemed to be good if rated at ISO 200, and that is where I shot it for several years.

NO MATH

I want to thank all those who offered suggestions and advice. Each post had something important for me. I had a very kind private message that gave me some good directions. I followed this directions and determined tat my film speed should be between 64 and 100 iso. The resulting negatives were just what I wanted. I stuck with the 100 iso for convenience sake. I am attaching a partial scan of one negative to show you what I came up with. Perhaps it isn't perfect, but it is a far cry better than what I had.

Now a problem I have has to do with printing. The scan looks great, but my print comes out very grey and muddy. There is no "punch" or contrast to the print. There are no deep rich darks as in the scan. I opened a new box of paper. I am using Arista edu glossy RC paper on a Beseler 45s enlarger with a color head. I have the contrast at level 2. The exposure was at f22 with 22 seconds. I am developing with Arista paper developer. My safelight is a Thomas Duplex Super Safe Light. I am sticking with the basic recommendations from the manufacturer until I get a handle on it. It obviously is my technique at printing. Any ideas?

Thanks again!

Attachment 154777

Less time, higher filter. Increase the magenta in the filter head. Try the equivalent of a 3. Don't feel that everything has to be aimed for 2 or 2.5.

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Originally Posted by Bill Burk

No the exact opposite is what they mean... to focus at infinity, you aim at a distant object. You will find the 4x5 view camera bellows is closed up most of the way when you are at the right focus position for a speed test.

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Or you can measure the distance from the lens board to the film plane and set it for the lens' focal length........L

I just wanted to give an update. I followed all your suggestions and carefully made tests, experimented and still was unable to get a print that was not muddy and lacked deep black shadows. I was ready to just about give up. Then I though that it could nt hurt to make another experiment.

I am shooting 4X5 Arista EDU ultra asa 200. I found my personal speed should be about asa 100. I was developing my paper, also Arista Ultra EDU in Arista paper developer 1:9 for 1.5 minutes and the rest as usual

I made one change, and began using Ilford Multigrade paper developer and magic happened. Now I am getting beautiful deep shadows, wonderful mid-tones and good highlights. So rather than formulas and negative work, exposure and so forth, all along it was using a paper developer that didn't produce good results for me. So I learned something. Thanks for your input.

Alexis

Following Michael R's point about 1/3 stops, could it be that you actually increased exposure 1/3 stop each time, but mistakenly counted whole stops when getting to your Z-I neg? If so, would that have actually been f32 you set and result in a 100 speed?

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Originally Posted by fralexis

I truly appreciate all your great answers and advice. However, my brain doesn't think in an analytical manner and all the information is confusing to me. In the end, I suppose I just need a simple yet clear method for determining my film speed. I know there are endless variables, but I can't process all that at my present stage of learning. All of you are far advanced in this process and I am just a newbie at the technical side of things.

Does anyone have a very simple and clear method for getting film speed? Then perhaps I can experiment and start thinking about the variables. Thank you so much!

Alexis

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Years ago I learned an excellent method to find the correct developing time and EI for any film. I think the 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 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 reciprosity 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.

A little late to the game, but my personal EI for Arista 200 is 40. Works well. Thanks for the tip on the developer, I'm going to try it.

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Originally Posted by fralexis

Does anyone have a very simple and clear method for getting film speed?

Alexis

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- metering a pair of black socks, with box speed
- exposing 4 stops less than given by the meter ( not to forget adding bellows factor)
- developing to recommended time

Should give nearly white socks with little drawings in the negative (zone 1, correct filmspeed)); if not - same procedure with slightly corrected film speed (longer or shorter exposure).

Finding zone 8 (correct development):
exposing a white t-shirt with 3 stops plus than given by the meter will do the simple but somehow clear trick and should give a black shirt with some drawings in the negative..

Ritchie

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source was an article by William Mortensen

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I have a lot of Mortensen books and articles, never saw this technique. Do you know where/when this was published?

Perhaps you have Mortensen's "On the Negative". I know that in that book he gives details in the "Ring Around Method" of reading a negative. I took the photojournalism course at Boston University in the late 60s-early 70s, graduating in '73.

This was all geared to 35mm technique. The instructor used and suggested Diafine for all B&W films. I wanted more and was starting to work with 120 film so I went across to the library and explored the photography books and it was there I found Mortensen. The photo-j crowd had their Diafine, and the fine artists at BU had Adams and the Zone System. At nearby MIT, Minor White had a big following. The mere mention of the name Mortensen was enough to get you black-listed, but his methods gave me prints I liked, so I persisted. The negative on the newsprint thing may have been from David Vestal, whose many articles I found very helpful.