Like many photographers I have a passion for the Black & White image. Like most, I have read dozens of books on how to improve your negs, prints etc. After many years and tens of thousands of prints I have found that it does not matter how good you are in the darkroom if the neg is not right then you will never get a great print. So I thought that I would set out the best way to get you negs correctly exposed and processed. Once you have this under control then your printing will be a pleasure rather than a chore.
FINDING YOUR TRUE B/W FILM SPEED
All film manufacturers are, to say the least, optimistic about the ISO (ASA) speed of their film. This is not to say that these speeds can not be obtained, but most of us mere mortals have to process in the real world and not a laboratory with controlled lighting exposure and development.
Having now said that how do you find out the real ISO speed of the film that you are using? The test that I am about to take you through is not new, Ansel Adams writes about it in his book "The Negative". If you are very serious about your processing, I recommend that you purchase this book and use it as your bible! The other point is, these procedures only work if your processing is very consistent. In other words if you are prone to wander off for a beer, coffee or what ever in the middle of processing, or even agitating a different way each time, this process will not work for you. Finally these tests only work in respect to Black and White film, also there is no magic film/dev out there. All modern films and devs do their jobs well, the main trick is to find a combination that works for you and stick to it.
First a few points on what you are trying to achieve with your negative. Assuming that you do not want a tonal drop out i.e. only Black & White on the print then you should be aiming for a negative that will give you a full tonal range that is printable on your type of enlarger. Where you place these tones is then open to your own personal visualisation at the time of printing. Remember the old adage, " It is better to have something to reduce, than nothing to increase ". What is the perfect negative, this to some degree depends to your own equipment and interpretation. I can only give you the principles of what to try and achieve, the final result must work for you, and in the way you wish to print.
When developed unexposed film will have a very low level of density this is caused by the action of the developer on the emulsion and is called chemical fog. As it covers all of the negative you just print through it, so therefore as long as is not too high (over 0.15) it is of no concern, as it only increases your print exposure time. I will refer to this as FB+f (film base + fog). An important point to remember is that exposure in the camera controls the shadow density and development controls the highlight density.
A good negative should have all the detail you want in the shadows while still retaining highlight detail that can be printed. When you process a roll of film the exposed part of the emulsion will show density in the form of a black deposit. The density of this deposit is measured on a machine called a Densitometer. This works by passing a known light value through the negative and measuring the amount of light loss. For a development gamma of 0.6 the readings will equate to approximately 0.15 per stop. This is the law of reciprocity in action. At high densities i.e. the shoulder of the characteristic curve the increase in density will reduce until no further increase takes place with increased exposure (reciprocity failure). As a general rule we are aiming for a density range of 1.20 above FB+f. This will result in a negative that will print on grade 2 paper on a diffuser enlarger. A density range of 1.05 will work better for a condenser enlarger.
The first thing that you have to find out is the true film speed. Your trusty (I hope) exposure meter gives you a reading that is half way between black and white. This is known as 18% grey (Zone V), the shadow detail that first prints is 4 stops less than the meter reading (Zone I), this is a density of 0.10 above FB+f on the densitometer. To conduct the test find an evenly illuminated white or grey wall. You can light a wall indoors but make sure that you use daylight balanced (5000 degree Kelvin) globes. Set the meter to the ISO on the film packet and make an exposure 4 stops less than indicated by the meter (Zone I), for arguments sake we will say the meter reads 30th @ f4. You expose at 30th @ f16. Keep checking the exposure reading between frames to make sure it is the same. You now need to do a series of exposures at 1/3 stop intervals i.e.
30th @ f16 = 125 ISO
30th @ f11_ = 100 ISO
30th @ f11_ = 80 ISO
30th @ f11 = 64 ISO
30th @ f 8_ = 50 ISO
1 frame with no exposure to light (leave the lens cap on).
Unless you are really keen or rich do this on the start of a roll use the rest to make pictures and process the roll in your normal developer and manner. The next thing is to find a densitometer if you do not already have one. All colour labs have them and most of the people there should be keen to help. Take a reading from the unexposed frame note this down on the film, this is your FB+f reading and must be deducted from all other readings. Now take readings from all the other frames you shot on the wall, note these down. As your eye is a excellent densitometer you can use these negatives as a comparison for future tests. The list may look something like these:-
Exposure Film speed Density FB+f Density increase
1. 30th @ f16 = 125 ISO 0.09 - 0.07 = 0.02
2. 30th @ f11 2/3 = 100 ISO 0.11 - 0.07 = 0.04
3. 30th @ f11 1/3 = 80 ISO 0.14 - 0.07 = 0.07
4. 30th @ f11 = 64 ISO 0.17 - 0.07 = 0.10
5. 30th @ f 8 2/3 = 50 ISO 0.22 - 0.07 = 0.15
6. No Exposure 0.07
As you can see from the above table the required density of 0.10 is on the 4th exposure, this corresponds to an ISO speed of 64. You will get different readings when you do the test, take the closest one above 0.10, but in most cases the true ISO is about ˝ the speed indicated on the box (or 1 stop). Remember if you do this the film company’s published development time will now no longer be correct. You must test and not try and take this tip as a short cut!
Next you need to find out how long to develop the film for. "Back to the wall" again (usual position for most professional photographers). This time you need to expose 3 stops more than the meter reading (Zone VIII), assuming nothing changed and the meter reads 30th @ f4 you will make an exposure of 30th @ f1.4, one @ 30th f16 (Zone I), plus one with no exposure. Use the rest of the film to make pictures then process the same way as the first roll. Back to the densitometer. Use the unexposed frame to find the FB+f, take a reading of the Zone I neg it should be the same, if your really good with your processing, or with in 0.02 of the first roll. Now a reading of the Zone VIII frame, if you are lucky it should read 1.20 or 1.05 above FB+f depending on the enlarger type you want to use. In reality this won't happen. If the reading is higher then the developing time needs to be reduced, if lower then increase the time. Change the developer times plus or minus 30 seconds and run the test until you get close to these figures. You should now have very printable grade 2 negatives if you use the ISO speed and developing times derived from this test.
NOW SOMETHING FOR THE REALLY KEEN.
The negative should be matched to your own enlarger. To do this a small modification needs to be made to the procedure above. The wall you photograph needs a little texture and cross light on it or use a piece of plain terry towelling. Make your exposures and determine the ISO and developer times. Now you can fine tune it. Take the unexposed neg and enlarge to an 8x10 size. Put a strip of grade 2 paper or multigrade paper with the enlarger set on Grade 2 in your easel. At 1 second intervals make a stepped test strip and develop in the developer for the time and temperature you normally use. Fix wash and dry. A tip if you are in a hurry:- dry with a hair drier or for 1 minute in the microwave, don't do this with finished prints only test strips. Now look at the step wedge and find the point where you can no longer see the difference between the steps. At this point you have reached D MAX or the maximum black that your paper/developer will produce. Set that time on your enlarger and put the negative that is 3 stops (Zone VIII) over the meter reading in your enlarger. Without moving anything do a test print, develop, fix, wash and dry. If you have the density range correct for your enlarger you should just see the texture of the towel. If the print is all white then reduce the negative development time, if grey then increase development time.
By now you have made the photographic suppliers rich and yourself crazy. It does seem a lot of work but the increase in quality you will obtain is well worth the effort. One final thing, if you change any of the above used in the test you will have to start all over again. Also if the results you are getting are erratic then look at your camera, the shutter may be playing up or suffering from thrombosis (clot behind the lens)! With films today they are all so close in their characteristics, that there is no magic developer or film. Stay with what you like and what works for you. Once this testing is out of the way you can concentrate on making award winning pictures.
Bruce Alexander
© 1999
