i,ve been using the zone system for over a year now and I´m happy with the results so far. Lately, i´ve been trying to use filters (red-cokin 003) basicaly and it gives me trouble calculating the less amount of light reflected by some objects and the extra amount of light reflected by others. There seems to be no way to exactly calcutalte the diference of what I see with and without the filter and therefore placing them on the zones. Marçal from barcelona, spain. thanks

-- marsal font vila (mussons@retemail.es), December 08, 2001

Answers

Does metering through the filter help?

-- Keith Nichols (knichols1@mindspring.com), December 09, 2001.

Metering through the filter, especially with orange and red, are usually not accurate. Here is what Ilford says on their website:

"Cameras with through-the-lens metering will usually adjust the exposure automatically when using filters. With some automatic exposure cameras, the correction given for deep red and orange filters can produce negatives under exposed by as much as 1 1/2 stops."

The best way to compensate for filters in B&W photography is to meter without the filter and then manually apply a filter factor. The filter factor should be calculated based on tests you conduct that take into account your film and geographic conditions. In areas of high altitude and/or intense sunlight, larger filter factors are often required. Filter factors are usually less for cloudy days, locations with high humidity, and tungsten lighting. You also need to take into account how much shadow detail you need in a particular image, because there is more blue light in the shadows than in objects reflecting direct sunlight (orange and red are "minus-blue" filters).

If you are using orange or red filters with Tmax-100 film, there are additional issues you will encounter that will require that individual testing be conducted to come up with your own filter factors.

-- Michael Feldman (mfeldman@qwest.net), December 09, 2001.

The filter factor stated on the filter is only a rough recommendation, since all depends on the colour sensitation of the film. Today manufacturers (sadly) no longer "code" additional information about the red sensitivity on the box. In the past there was the distinction between orthopanchromatic, panchromatic and superpanchromatic. The red sensitation is important for the tonal rendition AND the effective speed especially with orange and red filters. "Real" panchromatic films and superpan films had a higher than normal red sensitivity which gave them a higher effective speed under tungsten lighting. Many modern high speed films are panchromatic or superpan. Techpan is superpanchromatic. The higher the red sensitivity, the lower the filter factor and off course vice versa. Orthopan films were promoted as having a tonal rendition closest to the human perception under sunlight, but often they needed higher filter factors, although even in this group one cannot generalize. What I want to say in short: The only way to cope with your problem is to stick to one film and test it with your specific filter and find out the correct filter factor for your system. This is not terribly difficult and when done once accurate for a majority of situations. I never had problems measuring through a filter with a TTL system with yellow, although with red filters I can only recommend to bracket. There are many "invisible" factors that can change the image, including the relative humidity. Also one often does not previsualise the shadow enough.

-- Volker Schier (Volker.Schier@fen-net.de), December 10, 2001.

I think the issue here is not how to calculate the filter factor in order to just expose correctly, although it is also important and Volker has made a point talking about the red sensitivity of different films. What our friend is really asking is how to place different coloured areas in their perspective zones when he is using a red filter. Actually, this is a problem even when not using any filter at all, since most spot meters don't measure all the colours correctly. The solution is to find a colour corrected spot meter (the pentax meter can be made to measure all colours correctly by a special treatment) and then, if you want to use filters, you will be able to measure through them with your spot meter and be quite close to the real thing. Of course, with superpanchromatic films you will have to do some guessing, but I think that with films that have a relatively flat colour sensitivity curve from blue to red, it will be rather safe to trust the reading of your corrected meter. The exposure meter of the Nikon F5 is supposed to measure all colours correctly.

-- George Papantoniou (papanton@hol.gr), December 10, 2001.

I don't understand how a meter can be corrected to handle orange and red filters in B&W photography correctly for all films, since different films have different color sensitivities. I am not talking about special purpose films, but the ordinary B&W films that most people use like Tri-X, FP4+, TMX, Delta 100, etc. Kodak publishes specific filter factors for their films (on the US Kodak web site) and you can see there is a difference in the filter factors specifications that they give for each of their films. There is also a different rating for daylight and tungsten. Based upon my experience there is also a difference in the nature of the daylight itself, such as humidity, time of day, etc. Not to mention the difference between shadow areas and sunlit areas of the scene. I don't know how any meter can be corrected to handle all these situations automatically. As Ilford says on their web site, TTL meter readings can be underexposing as much as 1 1/2 stops for orange and red filters (assuming that the TTL meter is accurate without the filter).

-- Michael Feldman (mfeldman@qwest.net), December 10, 2001.

The Zone VI modified Pentax digital spot meter includes a filter pack specifically designed to match spectral sensitivity to Tri-X.

-- Sal Santamaura (santamaura@earthlink.net), December 10, 2001.

We have been talking about sensitivity of film and exposure meters so far, but somehow not about the device that has the largest influence: The filter itself. There is -- as far as I am aware -- no norm of any sort designating B&W filters. You will say that there are Wratten numbers, Schott numbers, Heliopan number, Cokin numbers etc. (and even lists telling you which wratten number ought to be the corresponding Schott number etc. ) designating each filter, but in fact the variations in density (easy to measure with an exposure meter) and colour (easy to see in a direct comparison between two filters supposedly "identical") are huge. Kodak may be able to suggest Wratten filters for a specific film, but this information will not necessarily (or most likely) work with different filters. Again I must say that bracketing is the only workable solution for red filters, since so many different aspects are involved beyond film sensitation, filter density and colour and colour accuracy of the exposure meter -- far to many to keep in mind or even to think about while trying to previsualize.

-- Volker Schier (Volker.Schier@fen-net.de), December 10, 2001.

Actually there is a way but does involve some testing. What I did was to take a picture of a gray card with the recommended filter factor and I bracketed around this exposure by 1/2 stop, I then developed the film on my developer of choice and took density readings of the negatives. The negative that gave me a 0.65-0.70 density was the correction factor that I used. This will work as long as you use the same meter, film and developer, if you change any of these variables the factor would change. In addition if you really want to get "exact" exposures, I also tested with the "new" factor that I found out the EI (exposure index) so that my shadows would come out as I envisioned them, as you found out, a red filter will "thin" out your shadows more than a regular exposure, or a green filter. so once you have a "correct" filter factor, test for the "correct" film speed for that specific film, filter combo. Good luck....

-- Jorge Gasteazoro (jorgegm58@prodigy.net.mx), December 10, 2001.

I think the best way to use filters with a meter involved is to meter through the filter. If you do grey card tests, it's fine, but what happens when the sun is coming up or the sun is going down or if it's high noon? Isn't it bluer in the afternoon? So, a red filter would have a greater affect on things. Correct me if I'm wrong.

-- Mark Wiens (mark@wiens.com), December 11, 2001.

You may be correct that a TTL meter will compensate for changes in color of the light due to the time of day. But the meter does not know the red sensitivity of the film since most films are different (see data sheets on Kodak web site). For a red or orange filter, the exposure may be off as much as 1.5 stops to begin with, before the TTL meter compensates for time of day. I have experienced this myself, especially in Colorado where there is more blue light in the shadows than many other places.

-- Michael Feldman (mfeldman@qwest.net), December 11, 2001.

Mark, as you say depending on the time of day the light is either warmer or colder, but the meter has the SAME sensitivity to the color, so it only compensates for the amount of light either lost or gained. The test are of the outmost importance because the film's response to the color is always the same, when I did my test I actually used a Jobo comparator card, with the three main colors the 3 main substractive colors and the shades of gray, you would be surprised at all the information you can get by using this.

-- Jorge Gasteazoro (jorgegm58@prodigy.net.mx), December 11, 2001.