B&W Contrast Filters

<p>I've read somewhere that if you compensate for contrast filters, you cancel the effect. Does anyone know?</p>

No That isn't true

<p>If you're asking about exposure compensation, nope, it will have little or no effect on the tonal relations of colors converted to grays by colored filters.</p>

<p>There may be some rare exceptions for certain monochrome films when used under certain unique lighting color temperatures, such as long exposures at night under street lights. Flickering or cycling artificial lights - notably some fluorescents and metal halide lights - may produce erratic results with "contrast" filters on b&w film. So can some artificial light dimmers. Likewise, theatrical or stage lighting colored gels may interfere with the anticipated effect of "contrast" filters on b&w films. But for typical use in daylight with normal exposure conditions, exposure compensation will not affect the tonal relationships of grays.</p>

<p>While yellow, orange, red, green and other filters are often referred to as "contrast" filters for use with b&w film, it helps to clarify how these work by understanding the relationship between the color of the filter and the colors present in the scene being photographed. There are many articles online that explain this, including on the websites for filter manufacturers like <a href="http://www.tiffen.com/tips_bw_filters.html">Tiffen</a>, and suppliers like <a href="http://www.freestylephoto.biz/black-and-white-filters-tutorial">Freestyle</a>.</p>

<p>For example, red and deep orange are usually regarded as "high contrast" filters because these darken blue skies to nearly black, leaving clouds relatively untouched, resulting in increased contrast between sky and clouds. But red and orange can also decrease contrast when, for example, used to photograph people with light or reddish skin who are wearing white clothing. The red and deep orange filters will lighten the skin, and have little or no effect on the white clothing. However, change the clothing to blue and the red and orange filters will darken the clothing, "increasing contrast" relative to the skin.</p>

<p>Orange and red filters can also decrease contrast between skin and blemishes, reducing the appearance of acne, blemishes, blushing, rosacea, freckles, etc. While that may be useful when photographing people without using cosmetics, it can also lighten lips and produce an odd appearance. (For this reason I usually prefer a medium or deep orange "digital" filter effect for my in-camera b&w JPEGs. The effect is usually flattering for most people, and I always have the raw files as backups if the effect doesn't work out as intended.)</p>

<p>And not all b&w films react equally to contrast filters and lighting color temperatures. Panchromatic films are reasonably predictable, but for critical applications it's a good idea to experiment with some test photos of color charts or other colored test objects using the desired filters under the anticipated lighting conditions. I found that the now-discontinued Kodak Portra C-41 monochrome film for medium format didn't reaction quite as dramatically to darken blues with my deep orange filter as did Tri-X, HP5+ and other silver halide films in daylight.</p>

<p>What are you planning to do?<br>

IF you shoot a color digital camera with a BW contrast filter mounted you can compensate against that filter in PP and get a BW conversion without the filter's impact or a right looking color picture . - Is it that what you read?<br>

If you shoot a BW sensor or film you can't compensate. You should adjust your exposure for the filter though.</p>

<p>Per Lex's response, if you put on (for example) a red filter, you're going to get very dark, dramatic skies. Can't see how or why you would "compensate" for that.</p>

<p>"Compensate" in the context of a filter and B&W film refers to exposure, not color. You have to compensate or you will get underexposed pictures. With a medium yellow filter you open up one f-stop. With a dark red filter you open up three f-stops. This gives correct exposure while maintaining the added contrast such as puffy white clouds popping out against a dark sky.<br /><br />I've never tried shooting with a red or yellow filter on a color digital camera with the intent of getting a B&W photo. I think it would be much simpler to shoot the image in color and then use a photoshop "filter" that simulates a real filter after converting to B&W.</p>

<p>Ok I see: exposure compensation, pretty much automatic with slr metering being through the filter. And yeah, blue skies with a red filter are still gonna look decidedly dark/dramatic.</p>

... but whether compensation is really needed does indeed need some closer, carefull consideration.<br><br>Using a contrast filter will change the tonal relation between the colour(s) the filter blocks and the colour(s) the filter lets through. Ideally, you do not compensate, because the blocked part is darker because that's what the filter is used for, and the unaffected part let doesn't need compensation.<br>Automatic metering through the filter however will see that the image is darker overall and will compensate. The result is that - though the tonal relation will not be affected - all parts are overexposed: the darker-because-blocked-by-a-filter part isn't as dark as the filter made it, i.e. isn't as underexposed as intended = is overexposed. The lighter-because-unaffected-by-the-filter part did not need compensation to begin with so is also overexposed.<br><br>Using deep red filters and such, filters that block most if not everything of the part of the spectrum they block, will also make the meter think the image has gone too dark. While overexposure ('compensation') will not be able to make the blocked part noticeably lighter, the meter trying to achieve that anyway will lead to an even greater overexposure of the parts that did not need compensation to begin with.<br><br>So overall, Iverson, what you read is correct.<br>That we get away with compensation anyway is due to the fact that both digital and chemical capture can take a bit of such uncalled for compensation.<br>And to the fact that filters do not allow 100% of all of the light through it is supposed to let 100% through, so a slight compensation (smaller than the meters suggest) is still needed.