advanced zone system filters - david kachel

5/2/2015 Advanced Zone System Filters

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Advanced Zone System Filter Use (Parts I&II)Part I: A New Approach to Filter Factors

©Copyright 1993 thru 2008 David Kachel

Article First Appeared in Darkroom & Creative Camera Techniques in July/Aug 1993

(You may print 1 (ONE) copy of this article for your personal use. No other reproduction, distribution or other use of anykind is authorized. If you have a friend with whom you wish to share this information, your friend must visit this web site

to get the article. You may NOT give it to another person.)

Filters are at once wonderful, and infuriating! In other articles I have described filters as both anindispensable tool that greatly expands one’s options for contrast and tone control; and as the greatestmonkey wrench in the works of Zone System photography, irrevocably dashing any hopes for precisecalibration and control.

In this series I will forego a review of the basics of filters, assuming you are already familiar withthem. However, for those who may need a refresher, I cannot recommend any better introduction tofilters than that contained in Ansel Adams‘ first series of books, Basic Photo Four, Natural LightPhotography, and to a lesser degree, in his more recent series, The New Ansel Adams PhotographySeries, Book Two, The Negative. Another very helpful book to have on hand is Kodak’s publication#F5, Kodak Filters for Scientific and Technical Uses. This last book provides detailed spectraltransmission characteristics for all of the Kodak Wratten filters likely to be used in B&Wphotography. Having this information is very helpful indeed. Naturally, the spectral informationapplies only to Wratten filters, so you may need another resource if you use filters, made by anothermanufacturer.

Problematic Subject

There is perhaps no other area of B&W photographic practice about which we know so little, as theuse of filters. I for one, certainly cannot claim to have all the answers—or even all the questions.Nonetheless, I do have some new information and techniques, and some little known olderinformation to share. There is also at least one rather startling surprise.

Filter Factors—A New Method

It has always seemed peculiarly ironic to me that we who use the Zone System, after expending somuch time and effort avoiding the average approach to exposure, development, and printing, shouldimmediately embrace it the moment we place a filter in the light path. But that is exactly what we dowhen we apply filter factors in the traditional manner.

In the Zone System we are taught to base exposure on shadows. But when we apply a filter and itsconventional filter factor, we abandon this concept, and instead base our exposure on a midtone. Yousee, a filter factor indicates the amount of additional exposure required to make a middle gray producethe same negative density with a filter as without—ignoring the shadows.

Although filter factors are based on reproducing a neutralcolored middle gray tone (such as a graycard), shadows are not inherently neutral in color. Most photographers would agree that exteriorshadows are rather blue, illuminated largely by blue light from the open sky. Filters that pass bluelight (blue, cyan, and magenta) will lighten shadows compared to a middle gray tone. Naturally, filters



that block blue light (yellow, green, and red) will darken shadows, compared to a middle gray.Therefore, when we apply a filter factor exposure correction, we are correcting for a sunlight andskylight illuminated midtone and allowing shadows to be pushed above or below their originalexposure placement. This happens because a filter will either increase or decrease the percentage ofblue light arriving from the shadow areas, compared to a middle gray.

Filter factors are based on a determination of the exposure increase needed to maintain the samenegative density for a gray card (Zone V), illuminated by a mixture of sunlight and skylight(approximately 5500°K).

In the Zone System we rarely base exposure on such a tone, but rather on a shadow tone, oftenilluminated by blue skylight alone. Therefore, it would make more sense to determine filter factorsbased on a gray card in shadow and on Zone III, rather than in sunlight and on Zone V. This wouldautomatically compensate for the previously mentioned influence of different filters on the exposureof blue illuminated shadows. Such an approach would also allow us to maintain the integrity of ourshadow–based Zone System exposure determinations—even when employing filters that canpotentially alter shadow density.

My technique is very simple. Set up a gray card in a shadowed area similar to that found in the type ofsubject matter you customarily shoot. Expose a control negative (no filter), placing the gray card onZone III. Then for each filter you employ, bracket a number of test exposures starting with themanufacturer’s recommended filter factor. Process all negatives for any given filter together with theirnofilter control negative. The filtered gray card negative that most closely matches the control willgive you your factor. (Don’t be cheap. Use a Kodak gray card—others may have a color bias.) Youmust use a gray card for this, because any natural subject could dramatically alter your test results—especially if it has any color bias at all. You should expect some of your results to differ significantlyfrom standard filter factors.

Now, because not all Zone System shadows are actually in shade, repeat this test with the gray card indirect sunlight. Once again, place the card on Zone III, not V. You will get different factors fromthose found in the shaded gray card tests, and also different from standard factor tests that generallyplace the gray card on Zone V, rather than III. The reason for these differences becomes apparent ifyou study Figure 1. Here we can see that the factor changes depending on which Zone we place thegray card, because filters also change the final Contrast Index of the negative. (For more informationon film contrast changes, see Part II.)



Determining filter factors by the shadowbased method allows us to remain consistent in our ZoneSystem practice, basing exposure on shadow placement (Zone III) even when employing filters, andreducing the under and overexposure problems frequently caused by filter use. Unfortunately, eventhis is not an ideal solution because filters are not so easily tamed.

Despite the effectiveness of this shadowbased approach to filter factor determination, it is stillnecessary to bracket filtered exposures (especially when using strong filters) 2 to 1 stop. The reasonfor this is twofold:

1. Few of the objects in nature on which we base our exposures are neutral colored; rather, theyhave some color bias which will cause them to shift exposure from the expected. Whenemploying our gray card/shadow tone based filter factors, colored objects in shadow will tendto be overexposed when we use a filter that passes that same color, and underexposed when weuse a filter that blocks that color.

2. The color temperature of light illuminating the shadows frequently varies significantly. Thiswill cause a change in exposure to the degree that the color temperature differs from thatpresent at the time we ran our tests. Warmer light will cause overexposure when employingfilters that pass red light, and underexposure when using filters that block it. Cooler light willcause underexposure when using filters that block blue light and overexposure when applyingfilters that pass blue light.

Unfortunately, the two examples I just cited are not the only instances of adverse influence on filterfactors and exposure.

Other Influences on Filter Factors



Color is a substantial influence in B&W photography, perhaps more than in color photography. Andthe effect that a filter will have depends very much on the colors and color sensitivities involved inevery step of the process.

I mentioned earlier that the color of an object in shadow can affect the Zone III shadowbased factorof the filter being used at the time. But the color

of the object metered can also adversely affect the accuracy of the meter reading itself, whether a filteris to be employed or not.

The spotmeter I own and use is overly reactive to the colors yellow and orange, and recommendsinsufficient exposure when these colors are metered. It is less than adequately sensitive to indigo andpurple, and recommends overexposure of these colors. Green will meter approximately correctly.

All exposure meters have disproportionate reactions to different colors and will mislead us whenhighly saturated colors are metered for exposure purposes. Fortunately, colors in nature are seldomvery pure, lessening this effect most of the time. However, it is a good idea to meter areas as neutralas possible. This way we can avoid the possibility that our meter’s disproportionate readings ofdifferent colors might compound the difficulties caused by applying gray card derived filter factors.

If photographing manmade, saturated colors, metering a gray card or other substitute might be a verygood idea.

Filter factors are also influenced by your film’s color sensitivity. For example, films with extendedred sensitivity would need a much lower factor for red, yellow, and magenta filters. Each type of filmhas different color sensitivities and therefore requires its own set of factors.

Reciprocity failure also plays a role, causing filter factor changes with longer exposures.

One of the most important influences on filter factors is something we do in the Zone System all thetime: intentionally altering film development. Using the traditional approach to deriving filter factors(i.e., gray card tests in sunlight on Zone V), we can see that N+ and N development wouldsignificantly alter the correct filter factor for each development scheme (Figure 2). Fortunately thenew method I proposed earlier in this article minimizes this effect by placing the gray card on Zone IIIinstead of V. Since the lower Zones are less affected by development changes, our Zone IIIbasedfactors will also be less affected. However, there will still be some degree of change.



There are three different ways in which filters affect contrast and tone. The first way is by changinglocal tones, the second by changing the Contrast Index (CI) of the film, and the third by changing thedensity range of the negative (different from CI) by producing an effective change in the reflectancerange of the subject.

Local Tone Changes

The newcomer to filter use is usually attracted by the fact that blue skies can be made darker byemploying a yellow or red filter, or by the tired old saw about separating red flowers from greenleaves. Although very useful, these commonly cited local tone changes hardly represent the fullpotential of local tone controls available with filters.

Local tones can be manipulated with filters any time there is a difference in local color or in localillumination.

Differences in local color allow us to employ a filter that passes one color and blocks the other. Theexample of red flowers against green leaves illustrates this quite well. However, there are more subtlevariations of local tone change available to us than the foregoing example suggests.

Colors in nature are neither pure nor uniform and this fact allows a great deal of latitude with certainsubjects. To take advantage of these facts you must carefully observe and analyze the subject andhave a thorough understanding of the characteristics of the filters you employ. A few examples mayhelp illustrate the potential for creative opportunities.



From time to time, I use a #11 (yellowgreen) filter to separate red tones. (I actually prefer the #13,but Kodak has discontinued this filter.) I recall discovering a sand bar running along a river in theAndes of southern Peru that had beautiful patterns in the sand. Some portions of the bar had a slightlydarker, more reddish color than the adjacent lighter and more yellow sand. The differences in tone andcolor between the two were very slight and couldn’t possibly have shown a significant tonaldifference in a photograph made without a filter. Neither would a red or yellow filter have been of anyhelp because they both would have passed virtually all the yellow and red light involved.

However, the yellowgreen Wratten #11 filter passes some red (closer to the yellow end of the redspectrum) and blocks some red (closer to the opposite end). Employing this filter produced a pleasingseparation in the tones of the sand bar, despite the fact that it was essentially all the same color. Itachieved this remarkable effect by cutting light near one end of the red spectrum and passing red lightthat was closer to the other end. This produced beautiful separation between the subtle patterns in thesand. (Although this technique worked very well, the photograph was largely a bomb in every otherrespect; my clever filter use being insufficient to save the image from other inadequacies caused bythe same clever fellow!)

Foliage offers a wonderful example for illustrating the subtle local tone changes possible with filterswhen there are variations in local color.

Leaves (excluding the obvious differences found in deciduous fall changes) offer a wide variety ofcolors, both from one type of leaf to the next and within the same leaf! Although appearing to belargely green, leaves can have a decided yellow or even blue reflectance, and though not visuallyapparent, frequently reflect a great deal of red light. (This little know factor, also called the WoodEffect, means that due to the high red reflectance of foliage, red filters employed to block green lightand therefore darken leaves will not be nearly as effective as one might think. Often a blue filter willdo the job better, because it will block both the green and red light, eliminating the Wood Effect.)

A magenta filter (I use the Kodak Wratten #32) can be used to differentiate the subtle colordifferences in yellow green leaves, lightening the portions that tend more towards yellow anddarkening those that tend toward green. The same filter will work with bluegreen leaves to lightenthe more blue portions and darken the greens.

You might think that a yellow filter would be useful with green leaves having yellow spots orstriations. However, if we examine the spectral transmission of yellow filters (the Wratten #8 forexample), we can see that this filter transmits green light just as readily as yellow and red, andtherefore would have no effect at all. This points out the importance of being familiar with the spectraltransmission characteristics of the filters you use, in addition to exercising careful analysis of the colorsubtleties of your subject.

Please bear in mind that the foregoing examples are not intended as suggestions of what to do undergiven circumstances. They are intended as demonstrations of the type of analysis and manipulationthat can be pursued with different subjects. Each subject presents different possibilities that aphotographer must evaluate individually, and then devise a filtration approach to fit thecircumstances. Sometimes the solution will work and other times it will not. Experimentation withdifferent filters (and ideas!) is highly recommended.

Using filters to manipulate local tones when there are differences in local illumination is anothervaluable tool. This possibility exists any time the same subject is illuminated both by sunlight andskylight.

A sidelit textured red wall in sunlight is a good example. The small shadows cast by the wall’stexture can be deepened by any filter that blocks blue light and lightened by any filter passing it.However there are different ways to approach this common situation.



If we wish to reduce local tonal differences we can do so by employing a blue filter to lighten thetextural shadows and darken the red wall overall. A cyan filter would also lighten the shadows andreduce the amount of red light reaching the film. Each filter would do this to a different, and largelyunpredictable degree. It is necessary to try both to see which gave the best result.

We are presented with similar options if we wish to increase the local tonal differences of the wall.Either a yellow or red filter would increase the effect on the film of the sunlit portion of the red wall,while reducing blue light from the textural shadows—once again to different degrees.

A green filter would cut light from the blueilluminated shadows while also reducing redtransmission. This would decrease local tonal differences if the reduction in red transmission weregreat enough and increase them if it were not. The only way to be sure would be to try it to find out.

Finally, we could use a magenta filter to lighten both the small shadows and the red of the wall.

As you can see, the effects of different filters on local tonal variations—both through manipulatingcolor differences and by taking advantage of differences in illumination—are quite varied and rich inpossibilities. They are also frequently not very obvious and require some careful thought.Furthermore, they are not very predictable. What worked for me on a sand bar in Peru may not workfor you on a sand bar in Minnesota.

In addition to careful thought and analysis, experimenting with different filters on the same subject isa very good idea. The day you get a wonderful tonal quality using the blue filter you were sure wouldbe disastrous, you’ll see what I mean.

In the concluding second article in this series, I discuss filtrationinduced contrast and density rangechanges, and provide some overall strategies you may find helpful.

Part II: Contrast and Density Range Changes

©Copyright 1993 thru 2008 David Kachel

Article First Appeared in Darkroom & Creative Camera Techniques in Sept/Oct 1993

(You may print 1 (ONE) copy of this article for your personal use. No other reproduction, distribution or other use of anykind is authorized. If you have a friend with whom you wish to share this information, your friend must visit this web site

to get the article. You may NOT give it to another person.)

In Part I , I introduced my new filter factor method and some other concepts about filter effects. Inthis concluding article, I’ll look a bit more at the unusual effects of filters on your film.

Film Contrast Changes With Filters

Everyone knows about tone changes with filters. After all, that is largely why we use them. We’d liketo see some colors rendered as lighter and others as darker grays—and we’d like to see moreseparation in adjacent areas of different color but similar tone.



What is not widely known is that filters also affect the actual contrast (Contrast Index) of the filmitself, regardless of the color of the object(s) photographed.

A number of authors (including Ansel Adams) have stated that red (Wratten #25 or #29) filters willproduce a higher CI than normal, while blue (#47 or #47B) filters will produce a CI lower thannormal, and that green (#58 or #61) will produce an approximately normal CI.

To be more specific, if you were to expose four pieces of the same film to the same stepwedge, onewith no filter, and each of the others through red, green, and blue filters in turn, then develop all fourpieces of film together at your normal processing time, the nonfilter and green filter scales would besimilar, while the blue filter scale would have a significantly lower than normal CI (about equal to N1), and the red filter scale would have a substantially higher than normal CI (about N+1). I repeat:these are actual changes in the Contrast Index of the film and are not due to other causes such assubject color or illumination. The end result of these CI changes is exactly the same as if you were toexpand or contract development of your film.

While doing my research on filters, I realized that this idea concerning CI changes with differentfilters has been repeated by many, including myself, and that I had never personally done any tests tosee if it were actually true. Neither was I aware of anyone else having done such tests. So I decided totest two films to see whether or not there was any validity to these claims. I chose TriX Pan and TMax 400 because they are excellent representative samples of old and new film technology.

The TriX Pan performed exactly as reported. Red filtration (#29) produced about an N+1 increase inCI while a blue filter (47B) produced about an N1. Green (#61) was similar to the no filter controlnegative. Less strong filters would of course produce lesser changes in CI. I feel it is safe to includethese contrast changes into my N number calculations when working in the field with filters andtraditional B&W films.

The real shock came from my tests on TMax 400. This film also exhibited contrast (CI) changes withdifferent filters, but the changes were completely different from anything I might have predicted.

Using a #29 red filter with TMax 400 produced an enormous drop in CI, equivalent to about an N2contraction — the opposite effect the same red filter has on traditional B&W films. Just as surprising,green (#61) and blue (#47B) filters produced substantial increases in CI, both about an N+1expansion.

I made inquiries at Kodak about these peculiar findings and they are consistent with Kodak’sobservations. I have also included these filterrelated contrast changes into my N number calculationsin the field.

I have no idea why these effects take place. Previous theories that red light penetrates further into theemulsion thereby causing more exposure and a contrast increase with older films seem feeble in lightof the results shown above with TMax 400. I have several hypotheses of my own, but absolutely noevidence to support them. I am certain only that the Contrast Index changes reported with differentcolored filters are real, very significant, and enormously different between traditional films and Tgrain films. I strongly urge you to consider including these differences in your own calculations.

Density Range Changes with Filters

In order to follow this discussion it’s extremely important to understand that I make a distinctionbetween a change in contrast (Contrast Index) and a change in density range. The latter is oftenmislabeled as a contrast change. Density range and Contrast Index have nothing in common, thoughthey are frequently called the same thing. A look at Figure 1a will help to differentiate betweencontrast and density range. It can easily be seen from this set of curves that several negatives can haveexactly the same Contrast Index (contrast) while at the same time having widely varying density



ranges. Figure 1b shows three curves having identical density ranges but substantially differentcontrast indices (CI). Although we commonly refer to a long density range negative as having highcontrast and a short density range negative as having low contrast, this is absolutely incorrect. Todifferentiate between the two, I like to refer to an increase in density range without a change incontrast as an “extension” of the density range. I call a decrease in density range without a change incontrast an “abbreviation” of the density range. I also speak of N+ “extensions” and N“abbreviations” of density range.


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In addition to the local tone changes discussed in Part I, and the overall CI changes mentioned above,you can also use a filter to cause density range extensions and abbreviations.

This is the simple result of the fact that filters will pass more light of some colors than others. Let’suse the Wratten #8 (K2 in older terminology) filter as an example.

This filter passes about 88% of the yellow light incident to it, without any increase in exposure (filterfactor) required. However, imagine that you have a Zone III shadow that requires a onestop exposureincrease when using this filter to maintain the same shadow density. This means that a yellow objectthat fell on Zone VII before using a yellow filter will have its exposure doubled by one stop and willtherefore contribute twice 88% (or 176% exposure) to the negative—when photographed through ayellow filter with a 2x factor applied. This will produce the equivalent of an N+1 negative densityrange extension (see Figure 2), moving the yellow tone from Zone VII to Zone VIII. However, it willnot produce expansion of the negative by increasing contrast. It will only lengthen the effectivereflectance range of the subject, and therefore the density range of the negative. The more saturatedthe subject and the stronger the filter, the more pronounced this effect will be.



You can achieve the same effect in reverse using filters that reduce light from colored object in higherZones. Using the same example as above, we could instead employ a blue filter. A Wratten #47 bluefilter passes virtually no yellow light and about 49% of the blue light incident to it. After applying afilter factor of say, 6x to keep our shadows on Zone III, the amount of yellow light passing throughthe filter will not have changed because the filter does not pass yellow light. This effectively movesthe yellow object down the exposure scale, shortening the subject reflectance range and also theresultant negative density range (see Figure 3). This will produce an abbreviated density range, butnot a change in CI. (This does not include the CI changes described in the previous section by using astrong blue filter.)



At this point I must mention that colors in nature are not at all pure —making filterproduced negativedensity range changes highly unpredictable at best. However, there will always be some extension orabbreviation of the density range unless higher tones are neutral gray. The only way to deal with thesechanges is to process only one negative of each subject, then adjust the processing of the remainingnegatives based on the results.

Metering Through Filters

I include this section largely because the literature is so loaded with suggestions to meter through yourfilters. Attempts to bypass the unpredictability of filters by metering through them can lead only todismal failure.

I did extensive tests using TMax 100, TMax 400, Professional Copy Film Type 4125 (see "ZoneSystem Expansion Film") and new filters (Wratten Filter Numbers 8, 11, 12, 15, 21, 25, 29, 58, 61,47, 47B, 32, and 44), all kindly provided by the Eastman Kodak Company for this and otherinvestigations related to this article. I wanted to see what the differences were between exposuresdetermined by metering through a filter and the correct exposure compensation determined bybracketing around a filter factor. Results are shocking.

The smallest differences for mild filters such as a #8 were 3 to q stops, while the differences forstronger filters were as much as 3 stops. In no case was the exposure metered through the filteranywhere near correct!

Then, I did tests to determine if there might be a constant difference between readings taken ofshadow tones through a filter and the factor actually required for that filter. If such a consistentdifference existed, this would allow me to meter through a filter, apply a known correction to thatresult, and get predictable performance — No such luck! As the color of the object being meteredchanged, so did the difference between filtered meter readings and the actual factor required. Such a

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method would work only if your subject is always neutral gray and always illuminated by light of thesame color temperature — nor very likely!

As faultridden as it is, the filter factor method is still the best way to determine correct exposure witha filter. This is especially true for the shadowbased method I described earlier in this article.

Choice of Filters

My personal choice for filters is Wratten Gelatin Filters from Eastman Kodak. My experience withWratten filters is that they have extremely high quality and consistency. I can’t say the same thing forother brands and types of filters.

Gelatin filters are sufficiently thin that they do not significantly interfere with light transmission, nordo they produce flare. They also do not add any additional air–glass surfaces to the light path. This isvery important to maximum optical performance. Although I can’t speak for all brands, in myexperience gelatin filters have been superior to other types I’ve used. In addition, Kodak providesprecise data on the spectral and dye fading characteristics of all their filters, which is very importantinformation to have.

A dozen gelatin filters also weigh a lot less and take up a lot less space than a similar quantity of glassor plastic filters, and are more cost effective because their one–size–fits–all nature eliminates thenecessity of having a different complete set of filters for every lens.

Finally, one manufacturer’s red (or any other color) is not the same as another’s and may not even bethe same from one production run to the next. Although they may appear similar to the eye, there areoften substantial differences from one filter brand to the next that will become apparent only in thefinal negative. There are no agreed upon standards for filters. This means that the only way to becertain you are getting the spectral characteristics you think you’re getting is to stick with a knownquantity, i.e. Kodak Wratten filters. I tend to think of offbrand filters in the same way I do of offbrand films: Thanks, but no thanks!

Putting the Pieces Together

There is no doubt about it. Filters take the nice neat little package of predictability and control wethought we had with the Zone System and blow its contents into next week.

The only way to deal with this problem is to either refuse to use filters, a head–in–the–sand approachthat denies us an extremely useful tool and doesn’t really make the Zone System much morepredictable anyway (for a spirited defense of this statement, see "Zone System Calibration"), or to bitethe bullet and accept the fact that the Zone System is not precise and doesn’t need to be. Since thebenefits of filter use far outweigh the annoyance of increased uncertainty, I suggest the latterapproach.

When applying any filter, to any subject, under any lighting condition, we can be assured that certaingeneral effects will occur.

First, because filters either pass a color or block it, virtually all tones in the subject will be changed toa greater or lesser degree by employing any filter at all. Even neutral gray objects are changed in tone—because filters also produce changes in CI. In theory, when a filter is used the only tone that is notchanged is that one tone upon which the factor was based. But as we saw previously, even this is notguaranteed.

Second, if there is a colored object in the upper subject Zones, employing a filter will produce eitheran extension (if the filter passes that color) or an abbreviation (if the filter blocks that color) of the

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effective reflectance range of that subject, and therefore of the density range of the negative. Thesechanges in density range can vary from insignificant to severe, depending on the circumstances andthe filter employed.

Lastly, most filters will produce a change in the Contrast Index of the film, independent of any otherfactors. Weak filters may produce a barely noticeable change, while stronger filters often produce avery substantial change.

Therefore, when we apply any filter at all, we know that virtually all of the subject tones will bechanged. We know that the negative density range will likely be altered, and we know that the finalContrast Index of the negative will also be affected. What we do not know in any of these cases is —by how much?

We can know what a filter is likely to do based on our analysis of the subject, knowledge of thefilter’s spectral characteristics, experience with that filter, and our own familiarity with the film weuse. However, we can never be certain the filter will perform as expected or to the degree expected.

The only way to effectively circumnavigate this near complete unpredictability is to first, bracketexposures ±2 to 1 stop when using filters, as previously mentioned, and second, avoid processing allthe film from one subject at the same time.

The way I approach this, to save time, is to process 5 or 6 negatives together, each from differentsubjects. This way my time in the darkroom usually isn’t lengthened, yet I still process only one sheetof film from any given subject at a time. It also helps minimize the effect of darkroom accidentsshould they occur.

If we process only one negative of a subject and have kept careful notes in the field, it is easy to adjustdevelopment of the remaining negatives of that subject based on the result obtained from the first. Ifnot using sheetfilm, one simply has to surrender to chance and guess at an appropriate processing timefor an entire roll.

I also find it extremely advantageous (make that, — essential), subject and time permitting, to shootone sheet of film without a filter so I will have a straight negative for comparison. This allows me toknow exactly what effect the filter(s) really had, and points out any exposure, contrast, or tonaldifferences that may have resulted from subject analysis errors on my part, rather than something thefilter did. This is a very helpful tool whether one is just starting to use filters or has used them foryears. I strongly recommend it.

Conclusion

Effective filter use comes only with experience, lots of experimentation, and careful preparation forthe unexpected. Filters force us to accept the unpredictable and imprecise nature of the Zone Systemand photography in general, while offering us a dramatic increase in the number of options availableto us for tone and contrast control.

For me, accidentally leaving my filters at home is just as big a disaster as leaving my film holders. Iimmediately turn the car around (this has actually happened) as they are an integral and completelynecessary part of the way I work. They also drive me absolutely nuts.—I hope they will do for youwhat they have done for me.

David Kachel

advanced zone system filters - david kachel

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