The film photography & darkroom work of David Kirby

How To: Understand And Use The Zone System

Ah yes, the zone system.  You've probably heard of it, you may even use it already, you may not even be aware of it's existence.  There are lot's of books and internet articles all about it, each with everyone's take on it, and they are indeed very helpful.  It is very easy to get into too much detail and if not careful you can end up becoming bogged down in extremes.  Before I go on to talk about how I use the zone system, we should actually look into what it is.

The Whatty what?!

Put simply, the zone system is a method pioneered by Ansel Adams & Fred Archer that allows us to obtain the best possible negative to print from.  When I say the best possible negative I mean one which has detail in the shadows and highlights but also maintains full tonality throughout the midtones.  It is mainly designed for those who shoot sheet film, but can be adapted to some extent by those of us using roll film or 35mm.  It is also mainly directed at those shooting black & white film but can be adapted to have an application to colour film.

How Does It Work?

Imagine a tonal gradation from pure black to pure white.  Actually, don't imagine - look below:

Image taken from Wikipedia  

Image taken from Wikipedia

Now let's divide this tonal gradation into 11 boxes of equal size:

Image taken from Wikipedia  

Image taken from Wikipedia

We then blend the tones within each box into the sum of its parts and give each one a number 0 to 10:

Image taken from Wikipedia  

Image taken from Wikipedia

This is the basis of the entire zone system.  Get this into your head, print it out and stick it in your field notebook (you do have a field notebook don't you)!  Each of these zones represents a tone within a negative/print as shown below:

Note that zones III, V and VII are in bold.  These are important zones.  Let's talk about zone V first.  Zone V is middle grey, which is what your light meter sees.  When you go out with your meter, be it hand-held or built into your camera you are, in fact, measuring middle grey.  Your meter is taking that light and sticking it right in the middle of the tonal spectrum, trying to ensure your exposure is balanced at the centre.  What about zone III?   Zone III is the darkest part of your image which will show adequate texture.  Think of it as the kind of detail you would see on a dark coloured, textured surface such as a black towel or canvas.  Zone VII is the opposite of zone III, the lightest part of the image which has retained texture.  Think of it as detail on a bright, puffy cloud or maybe detail on a wedding dress.  These three zones are the most powerful zones in the zone system.  Using them will enable you to have complete control over your final image.


That's enough about zones for now, let's talk about metering.  Spot metering is the way to go.  Well, for me anyway.  When using the zone system a spot meter is ideal if not essential.  I have never been a fan of incident and reflected light metering, I just can't get used to them, and spot metering just makes more sense to me.  Now, let's say you have a spot meter.  Find a good, rough textured, lightish coloured towel and wait for an overcast day.  Go outside and hang up your towel vertically so that it is evenly lit by natural light.  Take a meter reading.  That meter reading is middle grey or zone V.  All well and good.  Now, take that meter reading and underexpose it by two stops.  Your new meter reading will now place your towel onto zone III.  Go back to your original reading and overexpose it by two stops.  Your towel will now be placed onto Zone VII.  This is a process called placing.  You are selecting parts of your scene (in this case the whole scene of a towel) and placing it onto different zones.  This is a fundamental metering principle of the zone system.  By under or overexposing from your meter reading we can place components of our image onto the required zones.  If. in a scene, you place some textured shadow areas onto zone III you can then meter each part of your scene and see what zones they fall on.  These process of falling and placing are important components in our metering.  By choosing where we want our shadow textures we can see where other parts of our scene fall (tonally speaking) and develop the film accordingly.

Expose For The Shadows, Develop For The Highlights

You may well have heard this saying before.  It gets batted about a lot in photography and is the source of a great deal of discussion.  Essentially it is the golden rule of the zone system.  Our shadow tones are controlled by our metering at the time of exposure.  Our highlight tones are controlled by our film development. 

Did you know that your 100 ISO film may not be 100 ISO?  That 100 ISO is based on the film manufacturer testing their film in their laboratory using their methods.  Perhaps you agitate your tank more than they do, perhaps you do not have as much control over temperature while you develop, perhaps you take longer to pour your chemicals in and out of your tank than they do.  All of these factors and more will affect how well-developed your negative is.

A few simple tests will help you to determine the best ISO to expose your film at and the best time to develop your film for.  All it takes is a little time, a little patience and two rolls of film.  Shall we?

Test 1 - Maximum Edge Blackness

Test 1 is a very important step indeed and has to do with contact sheets.  If you are anything like I was a year or so ago then you only make contact sheets of your negatives as a reference to your composition.  But, a contact sheet is a powerful tool in the printers arsenal that, after this test, you will do for every roll of film you shoot.  Won't you.

When printing in the darkroom we reach a point in our paper exposure where the shadow areas are getting no blacker and the light from our enlarger is merely adding density to the midtone and highlight areas of our print.  What we want to determine is the shortest exposure time for maximum black to be reached when printing through the film base.

So, dig through your negative sheets and find a roll of film which has either a blank frame or a long blank bit on the start or end.  The film you use should be the film you wish to do your testing on as the zone system tests will have to be done separately for each black and white film you use.  Set your enlarger head to a height which you can easily set it to again and which allows the light from your lens to cover an area just larger than 8x10.  Find a sheet of your most commonly used 8x10 paper (RC is best as we don't want to waste valuable FB paper on a contact sheet do we) and place on your easel.  Lay your negative over your paper and place a sheet of glass over it.  If you have a contact sheet frame then even better, use that instead.  Make sure your enlarger lens is set to your usual printing f-stop and that your filtration is set to grade 2.  Now, make a test strip on your paper through the blank portion of your negative.  Process as usual and leave to dry before inspecting.  You should see a strip at which no more shadow density has been added to your print.  Your darkest strip which shows no difference to the strip after it is your maximum edge blackness printing time for this film, developer and enlarger height combination.  Remember that different films have different densities in their blank regions once processed so you will have to repeat this test if you use different black and white films.

Once you have completed this and the following tests you will suddenly find that your contact sheets become unbelievably useful!  They now show you exactly which frames are under or overexposed and which frames have the best highlight and shadow detail to print from.  This information makes it much easier to select the initial grade to start printing any one frame at.

Now this step is complete we can move onto the next test.

Test 2 - Determine Your ISO

These tests are slightly adapted from a method I found on the internet written up by Terry Staler.  The first test will allow you to determine the ISO you should rate your film at to ensure that what you meter as zone III is actually recorded on your film as zone III, i.e. What you meter as shadow detail is recorded as shadow detail and prints as shadow detail.

Grab your lightish coloured, textured towel from earlier and, on an overcast day, hang it up so that it is evenly lit.  Setup your camera on a tripod, load it with your chosen black and white film, mount your most frequently used lens, fill the viewfinder with the towel and focus on it.  Set your spot meter to your film manufacturers ISO rating and set your shutter speed to around 1/125.  Now, take a meter reading.  If you're fortunate then your meter will indicate an f-stop somewhere in the middle of your f-stop range for the lens you are using.  If it doesn't then adjust your shutter speed until it does, but try not to use a shutter speed slower than 1/30 or faster than 1/250. 

Now, close your f-stop down by 2 stops from your meter reading.  We are now placing our exposure onto zone III.  Fire your cameras shutter to expose your film.  Now, change the ISO setting on your spot meter to 1/3 stop less than the manufacturers speed rating.  If using a 100 ISO film then change to 85 ISO, take a meter reading of your towel and make another exposure 2 f-stops below that meter reading.  Change your ISO setting 2/3 stop lower than the manufacturers rating and, again, meter and expose at 2 f-stops lower than the reading.  Keep doing this for exposures 1 stop below, 1/3 stop above, 2/3 stop above and 1 stop above the manufacturers speed rating.  I recommend having a notepad to hand to write all of your exposures down.  Fill up the rest of your film with pictures of the dog or whatever is lying around and develop your film as you normally would. 

Make a contact sheet of the negative, making sure to print for maximum edge blackness.  Once dry, observe your contact sheet carefully.  Look for the darkest print in which you can still detect the texture of the towel and shadow detail is visible.  This print represents the exposure your film requires to place shadow detail on zone III.  The ISO you shot this frame at is the ISO which you should rate your film at from now on.  This test makes sure that when you take a meter reading and place it onto zone III, it will develop on your negative as zone III and thus will print at zone III.

Now, it's time for the final test.

Test 3 - Determining Film Development Time

So, we know that we can expose our film to ensure that shadow detail is recorded and therefore printed correctly.  But what about the highlights?  As we mentioned earlier, highlight tonality is determined by development time.  Test 3 will help you to determine the optimum time to develop your film for.

Set your towel up again and take your meter reading, ensuring that the ISO setting on your meter is set to the ISO you determined in the previous test.  Now, make an exposure 2 stops above this reading.  Fill up your whole roll of film with this one meter reading.

Now, this is where it gets trickier.  You need to cut your film up into about 4 sections (for 120 film about 4 or 5 inches per section) and develop them separately.  If you have two developing tanks then fantastic, you can load each section of film onto your reel in your changing bag and put the remaining sections into the spare tank until you are ready to process them.  Don't worry about the cuts being uneven, it doesn't matter. 

For the first section of film use the manufacturers developing time for your chosen temperature (usually 20oC).  For the second add 20% to the manufacturers recommended time.  For the third add 30% to the manufacturers recommended time.  And for the fourth add 40% to the manufacturers recommended time.

As in test 2, make a contact sheet of the negatives and leave to dry.  Now take a look at your print.  Look for the section of film which shows the slightest amount of good detail in your highlights.  The developing time which this frame represents is your standard developing time for this film from now on.  This time is known as N or "normal".


So let's review.  You have determined your optimum ISO to rate your film at to maintain shadow detail, and we have looked at optimum time to develop your film for.  We can now be confident that we can maintain both shadow and highlight detail in our negative.  Or can we?

Expansion & Contraction

Everything we have learned is all well and good but it is based upon the assumption that we only have 5 zones of textural tonality in our scene, ranging from zone III to zone VII.  Most of us will know that this simply is not the case most of the time when we are out shooting.  We may be out shooting on a bright sunny day with a scene containing 7 stops of tonality (high contrast), or we may be out on a grey, flat day with only a 3 stop range of tonality in the scene (low contrast).  If we processed our film as normal we would find blown out highlights in the high contrast scene and dull, grey highlights in the low contrast scene.  Can we do anything about this?

Happily, yes it can!  As we mentioned earlier highlight tonality is controlled by film development time.  By simply decreasing or increasing our development time we can control our highlight detail.  This process is known as expansion (extending development) and contraction (reducing development).  The goal is to create a negative which has a 5 zone range of textured tonality (zones III to VII - remember you can have non-textured shadows and highlights in a negative).

Remember earlier how we referred to our developing time for a negative with 5 zones of textured tonality as N?  Now we can subtract and add to N to create the following:

So how do you work out your personal development times for N- and N+ development?  Normally you would have to carry out further testing as before, developing sections of film for varying times and seeing how it prints.  Personally I determined my times as seen in the table below:

As you develop and print from these negatives you may end up tweaking your times to suit your style more which is totally fine, that's what the system is for!

The Roll Film Problem

If you are shooting sheet film then hurrah, you're sorted.  For those of us shooting roll film however we now encounter a new problem.  We are likely to have different frames on our negative which all have differing zonal ranges; one frame may require N-2 development whereas the next may need N+1 development.  What can we do about it?  Not a lot to be honest.  All you can do is decide which frames are the most important and develop accordingly.  Alternatively, if you have a system-based camera you can opt to use a different film back for each development.  The drawback is you will be constantly swapping backs and, if you're a landscape photographer, you have to cart a load of film backs around with you each time you go out.  This is where filtration can come in handy.  I almost always use filters in my photography and neutral density grad filters are particularly handy for bringing down the tonal values of bright, sunny skies.  A little use of filtration at the time of exposure can save a lot of hassle down the line when it comes to determining your developing time.

Final Review

If you have made it this far then I salute you!  This is one long article and is a bit of brain killer, even writing it is hurting!  Now I recommend you relax, take a breath and ponder on the fact that you now have complete and total control of what is recorded on your negative and what comes out of your darkroom.  Let that sink in as your grin starts to grow.

Personally, I rate Ilford FP4+ at 80 ISO and have an N development time of 15 minutes in Rodinal.  Since doing these tests I have seen a marked improvement in my negative quality which has made printing easier.  Well, I say easier - I still get the odd pain in the bum frame to print, but who doesn't love a challenge?!

Well, I leave this with you now.  I recommend doing a few re-reads so as to get the basic principles fixed in your mind.  This tutorial is by no means exhaustive and I am no expert in the zone system, it is but a scratch in the surface of zone system knowledge.  If you want to read further I recommend Ansel Adams book "The Negative" and "The Practical Zone System" by Chris Johnson.  And, of course, the internet.

Hopefully some of you have found this helpful.  It was a killer to write so i'm on my knees begging for someone to find it useful!

As opposed to my usual sign-off I have decided to go with something more appropriate to this article.  So, until next time, happy metering!