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Friday, March 6

The whys and wherefores of test strips

Contributor David M. continues his look at the essentials of the darkroom with a comprehensive guide to one of the simplest but most important "tools" in the printer's armoury.

A good test strip should give you most of the information you need to produce a
satisfying print.

The Stripper

Here is one of the most encouraging things that I ever learned. There are some things that the great darkroom printers do, and we can do all of them ourselves. This is the greatest lesson I learned from watching a printer I admired. He (it was a he) didn’t do anything that I couldn’t do, and do easily. It was not like making Benedictine or becoming an MP. There were no secrets at all.

Here is what all the great printers do. Put the negative in the negative holder, at the top. Switch on the enlarger. Move the enlarger head up or down to the right place. Focus. Switch off the enlarger. Put the paper in the masking frame. Stop down the lens. Switch on the enlarger again. Switch it off again. Develop the paper and fix, wash and dry it. I could do all of that. In fact, it’s what I did already. That, believe it or not, was the lesson.

That is what everybody must do. There are other things that people do, like dodging and burning, changing paper or filter grade, using different developers, toning, bleaching, spotting and host of other refinements, but an actual, real print can be produced without them. It might not be the best possible print, but it will be a print, nonetheless.

Some items are idiot-proof. (Well, nothing is altogether proof against a really dedicated idiot.) Our first doubt will arise when we come to the second switching on and off. Easy, yes, but for how long?

It’s possible to buy all sorts of devices to decide this time for us, but we can rely on our own eyes and our own judgement.

First, we shall make some tests

Let’s assume that we are going to make a 10x8 print for no better reason than that it’s a very common size. We’ll assume that we’ve chosen the negative (clean it first) and got as far as focusing it and stopping down the lens. Most people find that stopping down two or three stops works well. Take a sheet of 10x8 paper and tear it into four 5x4 pieces. A reasonably sized test strip will avoid wasting much more paper later. Put them back into the box, emulsion side up (so we know which is the right way up when you take them out again) and close the box. Use the same paper that you will use for the final print.

Don’t forget that this is all done under the safelight.

Open up the lens fully and examine the projected image. Choose a part that seems to go from darkest to lightest, or one that is pictorially important. Switch off the enlarger and stop down again, then place one of the quarters on your chosen part of the image. It doesn’t have to line up with the sides. Set your timer (some people don’t use a timer but for me, it’s essential) to something like four seconds and expose the whole sheet. (This is my own starting point, but yours may be different.) Cover up a strip at one end with an opaque card and give your timer another click. Do this again and again, covering up an additional strip each time, until you reach the end of the paper, taking care not to move it. About half-a-dozen strips should do. (A sheet of glass or some small weights or magnets will help to keep it still.)

Develop it in your usual way, then when it’s fixed and rinsed, have a look at it in decent light.

Ideally, you will see a series of stripes progressing from much too light to much too dark with a couple that look more-or-less right, somewhere in the middle. It’s very important that both ends are wrong. If you think that one of the ends looks right, you must do it all again, because if the strips are getting better and better, just when you run out of paper, how can you be perfectly certain that the next one won’t be better still? You might believe that you can judge something that isn’t there, but it’s not true. You will simply waste more paper, time and enthusiasm. If all of them are too light, either open up the lens by one stop or increase the time to twice the time you set and do it again. If they’re all too dark, close the lens by one stop, or reset the timer to half the time.

And repeat...

I’m afraid there’s no alternative to doing it again, but the next test should give you a much better idea of the sort of exposure you are going to use for the actual print. If this is your first time, you might possibly need to do a third one, which is unlikely, but not improbable. You still have two more pieces of torn paper to play with. The next time you’re printing, you’ll be much closer from the beginning. After you’ve printed a few more of your own negatives, you’ll have a better idea of what your system prefers and have established your own convenient starting point.

We shall imagine that your second test strip has produced a strip that you think looks right. It’s possible that there are two equally attractive strips. In that case, you can, if you wish, make another test strip to decide. You must give all the paper the same number of clicks as the lighter of the two, then re-set the timer to half the time and continue to make another test strip as before to give you a more detailed choice. You’ll be very close. I usually guess. Develop and examine. Make up your mind which one you think is best. Now you’re getting so close, you might want to give a little thought to the contrast of the print, because any major contrast problem will be evident.

If the indicated time is very short, it might be sensible to stop down one more stop. A longer time will be useful when dodging and burning, when you make the final “fine” print.

Some people like to make their test strip in reverse, covering up all but the first strip and successively exposing parts of it. The effect is the same – a series of exposures at known intervals, each strip with one click more.

Now you have established a basic exposure we shall make our first print.

Take a whole sheet of paper and put it in the masking frame without altering anything else. Expose it for the same number of clicks as the best test strip. Develop, fix, wash and, if you have time, dry.

This print is the first time you will see your whole image and will act as a guide to what to do next. Examine it carefully. Facial expressions will be clearer. You will often want to change the cropping or framing a tiny bit (Leica owners may ignore this.) You might even revise your opinion on how light or dark the print should be, or how contrasty. It’s probable that one part of the picture looks just right and another part looks a bit wrong. Seeing all these things is why you made this first straight print. You are ready to go on to darkroom glory.

Not all clicks are equal

There are two advantages to using the same number of clicks for the print as you used for the test strip. Firstly, it seems to be agreed that several clicks that add up numerically to the same overall time don’t produce quite the same effect on the paper. The usual explanation is that the lamp takes a little time to warm up each time you click and may get a little hotter and brighter during a single long exposure. It’s not a big effect, but you should know about it. Not re-setting your timer saves time and removes a small source of error.

Secondly, when you come to dodging and burning, the test strip will give you a good idea of what one click more or less will do to the print. You can then dodge or burn by using the right number of clicks – much easier to remember and even record. “+2 clicks” will apply to any print you make, whereas “+2 seconds” will only apply to one specific size. You might use the back of your straight print to keep notes and diagrams for when The Tate buys a copy.

Please note: I like simplicity and this seems the simplest way to make test strips, but it may not be the best. There are other methods, which involve using progressively different lengths of exposure for each successive click, which gives a scale that’s co-ordinated with f-stop numbers. The people who prefer this method speak very highly of it. They write extensively on the web.

Some people like to move the paper along, so that each test exposure is made from the same part of the negative. This has much to commend it, particularly if it’s vital to get one small part of the image (perhaps a face) exposed correctly. It is a bit more trouble and you may need to construct a simple but ingenious device to do it.

We have tacitly assumed a normal grade of paper or filter with a normal negative and we have not mentioned dodging and burning. Your first print will give you a good idea of these things, and experience will tell you when you should change the paper grade or dodge and burn. You will often need both, but it seems sensible to settle on the right grade of paper for the whole image before deciding to dodge and burn bits of it.

Beware the trap of increasing contrast to make the print look better in the relatively dim light of a darkroom. Impact isn’t everything we want from a print, so make this decision under normal bright light. It’s even better to dry the print first, as there’s something called “drydown” that slightly changes the look of a print and may influence your judgement, particularly if the highlights are important.

If the paper grade is right, your dodging and burning will be done for creative reasons and not as a print rescue mission. Dodging and burning is another subject…

In praise of small things

Test strips are all well and good, but making test strips seems to take time, involves mental arithmetic and uses valuable paper. For a beginner, it can seem like a hopelessly time consuming ritual. We long for the moment when that enchanted shadow gazes back from the developing dish. Perhaps, psychologically, we need to suffer from a problem before we embrace the solution.

Kodak used to make a small device called the Projection Print Scale to help in getting reasonably close to proper exposure in the darkroom. It was a small sheet of transparent plastic with a pie chart of progressively increasing densities that you placed on top of a piece of paper under the enlarger.

Then you gave a single exposure to the whole sandwich and developed the resulting print. Somewhere on the pie chart would be an exposure that was quite close to the one you wanted. Not perfect, but for a beginner, or indeed, anyone faced with an unfamiliar tricky negative (all negatives are tricky to the novice) a very handy guide. I seem to recall that it was considered rather infra dig to use one.

Kodak seem to have abandoned this handy and helpful device but if you go to this Firstcall Photographic page you’ll find the very thing.


Jan Moren said...

The example image at the top is, sad to say, not a great example. More specifically, it looks pretty much great as-is, if only the sharp transitions were blurred out.

Bruce Robbins said...

Well, all I can say is it worked for me, Jan. One test strip and the following straight print:
If only they were all that easy. :)

Bernard L said...

Adding equal increments of time (4s in your example) is not ideal: between first and second pacthes, time is doubled (too much change); between 10th and 11th step time increases by 10% (hardly significant). May I propose my method? After misplacing my stopwatch, I work with a metronome. Typically I'll start with smallest exposure 12s (count 1, 2... 12). Move dark slide over test strip one increment; count 12, 13...16, switching on at start and off at end. Because I get the tempo of the metronome even before the start, I estimate the exposures are accurate to 1/10s. Next, count (16, 17...20). Next (20, 21... 25). List of cumulative times 12, 16, 20, 25... sounds familiar? Chances you already know that series of numbers!
Reaxon for that choice: constant increment in relative value. And small enough (1/3 stop) that one can nail down exposure on hard paper (grade 3).

Doug H said...

I use a home made version of the f-stop timer by RH Designs of UK. On my Gralab I've marked off with glo-paint increments of 3/6/12/24/48 seconds. With a whole sheet of paper in easel, I then move the card along for each of those increments. Their web-site has a very good essay on the importance of f-stop timers.

Paul Blanchard said...

Nothing wrong with a Kodak enlarging exposure scale. It permits you to make a comprehensive test on a piece of paper about 5x4 or even less if the area is selected with care. It certainly saves on paper when making 20x16 prints!

DavidM said...

May I suggest that everyone is right. There's no perfect method, and we must all do what we prefer or what we're used to, or what suits the equipment available.

I'm another one who like the look of Bruce's test strip – it looks like an interior with one shadowed and one bright side. I like the minimalism. Hard to get it right.
For myself, in this case, I'd have made the strips by moving vertically, rather than side to side, or even moved diagonally, but that merely illustrates the individuality it all.

Bernard: A proportionally scaled increase is entirely sensible, but it's a little bit more trouble. At least, I found it so, but I was setting and re-setting a timer. I have tried a metronome (Paterson made a special photographic one) for printing, but found it awkward.
The series I'm familiar with is 11, 16, 22, 28... rather than the one you quote. I'm afraid that I don't quite understand yours and I'd be glad of further explanation.

Doug: If we use the series of 4, +4, +4, +4, +4 ... instead of your own (entirely rational) suggestion of 3, 6, 12, 24, 48, then the central value will be 12 seconds in both cases. I generally like to have the preferred value in the centre of the test strip. Marking times on the Gralab is something I hadn't thought of.

Paul: I agree with you, but I think the key lies in the phrase "...selected with care."

I can't defend this method of equal times other
than on grounds of simplicity. For a beginner, I think that's important. For me it seems to work well, and I like my scaleable system of dodging and burning by clicks. I should confess that I have sometimes adjusted the click intervals, so as to give me four clicks per basic print, to maintain the easy dodging and burning, but this is a secret personal vice.

Joe Iannandrea said...

I notice Doug's method has the added advantage of exposing the whole test strip in a single run instead of a series of short exposures. This way if the best exposure on the test strip is 24 seconds you can just set the enlarger timer to 24 seconds and go. The alternative, clicking out six 4 second exposures, doesn't sound like a big deal until you consider doing it while juggling dodging tools at the same time.

DavidM said...

Yes, I quite like Doug's method.
When dodging and burning I find that the click method works well. Suppose I want to burn in the sky by one click, which I've determined by examining my original test strip. I also want to hold back a face by two clicks. After that, I may want to do some edge-burning for aesthetic reasons.
Assuming that the best test strip is six clicks, as Joe suggests, I give four clicks basic exposure, then pick up my bit of black card on a wire and give two more clicks, using one hand for the timer and holding the wire over the print with the other. I put down the wire and pick up my black card. I'm doing this changeover while the enlarger is off, so I can allow myself to fumble. I hold the card over the print and give one click for the sky, again switching with one hand and moving the card, as you do, with the other. Then I can edge-burn each edge with one click, or whatever, in the same way. If the edges need less than a whole click, I adjust this by the way I move the black card. If I needed to burn in the face instead of dodging, I'd use a card with a hole in it.
Some people prefer to use their hands for both dodging and burning and this can work very well for an experienced printer.
I think that the significant part of all these methods is to have properly known times, however they may be derived, to give controlled and repeatable exposures to the final print. They all seem have merits. It's the print that matters, after all.

Bernard L said...

To DavidM

The numbers I propose are just the series of ISO film speeds. Here they are in full: 10, 12, 16, 20, 25, 32, 40, 50, 64, 80, 100; and then same again, only x10. 3 steps result in one doubling, so one step is 1/3 stop. Once you have memorized these 10 simple numbers, the complication vanishes. And 1/3 stop increments (rather than doubling or half-stop increments) are welcome when printing on #3 or harder paper.

DavidM said...

Thank you. I understand now. A very neat bit of thinking.