Exposure with #25 red filter

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Hi All

I am starting to experiment with a #25 red filter and have had some mediocre results. Basically, deep blue skies are still somewhat washed out. I use a TTL meter and it has been working fine- i.e. compensating by 3 stops.

My question is: When using the filter, should I simply continue metering as I have always- i.e. place a shadow value in a desired zone, or should I meter off the blue sky and place it in a visualized zone such as Zone II or III to get the desired effect.

Thanks



-- Asher (schachter@a1.tch.harvard.edu), September 15, 1999

Answers

Have you tried combining the #25 with a polarizer? I bet that the reason that your skies aren't jet black is because the sky itself isn't pure blue.

I get the same results as you with using Kodak HIE. I don't get a jet black sky unless I use a polarizer. Then the sky will turn black, because it's finally pure blue.

When using filters, meter as normal, and then factor in the filter compensation. For instance, use an incident meter and open up three stops for the filter. The best thing to do is put the filter over a spot meter, and then evaluate your scene through the filter.

A red filter will not only produce a dark sky, it will also lower the light in shadow areas. The light in shadows is blue, and it comes from the sun light being defracted by dust particles. Take a look in "The Negative" by Ansel Adams. That book really goes into the effects of filters.

-- Brian C. Miller (brianm@ioconcepts.com), September 15, 1999.


Thanks Brian

I haven't tried a polarizer in a while since I am using a rangefinder which makes it a pain to use polarizers. I have just bought a better (B+W) red filter and it is a significantly deeper red than my old #25- maybe that will help.

I will certainly keep an eye on the shadows, more so than usual, as you suggest. I'll also brush off the dust from my copy of The Negative and remind myself of what Ansel had to say about this.

Thanks

-- Asher (schachter@a1.tch.harvard.edu), September 16, 1999.


Try metering off your palm and call it Zone Six...t

-- tom meyer (twm@mindspring.com), September 17, 1999.

Meter normally.

-- Joe Cole (jcole@apha.com), September 21, 1999.

Its not simple. Meter sensitivities and film sensitivities differ. You will be beset by perceptual problems. The filter factor normally published is based on reproducing a middle grey. Do a quick test with your meter on a grey card and try reading without and with various filters and see if your meter recommendations match the published filter factors. If not, don't worry. A lot of silicon meter cells are overly sensitive to red and not as sensitive to blue (exactly the opposite of most film). My meter suggests underexposure on the red end and mild over exposure on the blue end. Its also a good idea to remember that filters selectively pass different wavelengths which means depending on your subject, you anyway need to use different filter factors. If you use a yellow filter on yellow sand, you probably need very little compensation for the sand to reproduce the same way but since the yellow blocks blue light and the shadows on the sand are illuminted by blue skylight, the shadows will drop down. However, if your main subject is blue, you will obviosuly need a lot more compensation to render your main subject areas well. With respect to skies, part of the problem is indeed that the sky reflects a variety of wavelengths, not just blue. After all, if it was blue, then yellow filters should darken the sky the most. The truth is there is quite a bit of green in the sky which is why red filters (which block blue and greeen) are more effective at darkening the sky. Check your negatives. Have you used too high a filter factor? Have you lost your dark areas i.e., do the areas in your neg which should be dark, actually end up showing texture? If that's the case, odds are you used too high a filter factor and overexposed your neg a bit. In other words, you will have situations where you can maintain shadow detail with less exposure than is dictated by the filter factor. That may well serve to increase the local contrast in the sky area. In extreme situations, the polarizer+red will work well too. DJ

-- N Dhananjay (ndhanu@umich.edu), September 27, 1999.


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