DecaMired Filters - Basic Tools for Color Correction

	*Color Temperature Meters and DecaMired Filters*

	We've all seen it - color photographs shot in available light with crappy color balance. Sure, sometimes we can get away with saying that it adds to the mood of the image, but usually it's just bad color, plain and simple. A lot of bad color can be corrected during printing or scanning, but not all images are printed or scanned. Besides, I'm the kind of guy who likes to get it right IN THE CAMERA. This is especially important when shooting color transparency film that will be projected, or if your client is going to see the images on a light box.
	If you shoot color transparency film, you most likely have a couple of color conversion filters in your bag. Two of the most common filters carried are the 81A, a warming filter that allows the use of 3400°K photofloods with Type B (3200°K) film (also common for use when the subject is in "open shade"), and the 80A filter, which corrects daylight film for exposure with *3200°K lamps. While those two filters can be handy, they are not necessarily the best solution to achieving correct color balance in the camera, nor are they all that's available.*
	So how can you tell which filter to use?
	Well, you could shoot a Polaroid, but that doesn't help you if you don't have a Polaroid back for your camera, besides, Polaroid is not always a good indicator of color balance. A better way is to use a color temperature meter.

	*Meter Options*

	There are a number of options for color temperature meters from, dedicated tri-color meters, to attachments for system meters, to low cost 2 color meters. Tricolor meters, though rather expensive, are the ONLY solution if you're using fluorescent or non-continuous spectrum light sources. For most of us, a simpler (and much less expensive) two-color solution works fine.
	Some Typical 3 Color Meters
				The Gossen Color-Pro 3F meter shown here can do it all. Let the meter know what film type you're using, and it will give you light balancing information in Mired or Kodak Wratten values. In addition, the Color-Pro 3F will indicate in CC filter values the correction required, for example, when working with fluorescent lighting. This meter will work with both continuous lighting and flash, so finding the correct filter for those uncoated flash tubes becomes a snap. All of this does not come cheap though, it has a street price (as of 12/2004 at B&H) of $1,081.95. One drawback, the Color-Pro 3F is not an exposure meter, so you'll still need another method for dealing with that requirement.
				The Konica Minolta Color Meter IIIF is another fine 3-color meter. Like the Gossen Color-Pro 3F, you tell the meter know what film type you're using, and it will display light balancing information for both continuous lighting and flash. As with the Color-Pro 3F, it's not inexpensive. The street price (as of 12/2004 at B&H), is $919.95. Once again, the Color Meter IIIF is not an exposure meter.
	What About 2 Color Meters?
	If the price of tricolor meters gave you a taste of sticker shock, you're not alone. Unfortunately, there are no 2 color meters being made today. Fear not, there's always ebay...
	The System Meter Approach
	I have to admit to being a fan of Gossen meters. I use a Gossen Luna-Pro F and an Ultra-Pro on a regular basis. There is a close cousin to the Luna-Pro F which is of interest to our discussion, the Luna-Pro SBC. The Luna-Pro SBC was the original heart of the Profi-System of intelligent attachments for Gossen light meters. The Ultra-Pro, which has a digital display, was a later addition, but retained the capability of using the Profi-System attachments of the Luna-Pro SBC. A distinct advantage to using a system meter is that you retain all "normal" light meter functions, just remove the attachment! Sadly, neither the Luna-Pro SBC nor the Ultra-Pro are currently being manufactured. Happily, they are almost always for sale on ebay.
				Before I go too far, let me caution you not to confuse the Luna-Pro SBC with a standard Luna-Pro or other model in the Luna-whatever line. The Luna-Pro SBC (and the Ultra-Pro) have 3 sockets on the business end of the meter (below the sensor cell window) that allow the attachment of the various Profi-System accessories. All of the attachments for the previous models of the Luna-Pro, such as the 7.5/15 degree vari-angle attachment, will fit the Luna-Pro SBC and Ultra-Pro, but the Profi-System attachments will ONLY fit those meters for which they were designed. There may be early models of the Luna-Pro SBC that were not equipped for the Profi-System that I'm not aware of, so make sure to check before buying. SBC models that say PROFI-SYSTEM on the faceplate are a safe bet. As an aside, the Multibeam 1/5/10 degree spot meter attachment is great, as is the Lunasphere, a large incident dome attachment. Those accessories alone are worth the price of admission to this system.
				Having said that, there was a wonderful attachment for the Profi-System that will convert a Luna-Pro SBC or Ultra-Pro into a 2 color meter - the Luna-Color (also known as the Profi-Color). While not as versatile as the tricolor meters, these attachments will serve very well for determining how much warming or cooling filtration you need for good color balance in every situation except those involving fluorescent or other non-continuous spectrum light sources. These are also not in current production, but may be found used through many sources. I paid $100 for mine from an ebayer in Sweden.
	What About Other 2 Color Meters?

	The old standby of 2 color meters is the Gossen Sixticolor. It doesn't use as fast a sensor (nor as sensitive) as the Luna-Pro SBC or Ultra-Pro, but if you want to find out just how "cool" the lighting is in the open shade you've been shooting, or if that lamp in the living room needs a bluer filter, the Sixticolor will do the job. Oh yes, forget about using a Sixticolor for measuring the color temp of your flash, that's not going to happen. These pop up all the time on ebay for about $50 or so, depending upon condition.


	*DecaMired (DM) Filters*

	*What the heck are they?*
	As I mentioned in the introduction, you may carry an 81A, 80A, 80B, or one of the 85 series filters in your bag. While these can be very useful, they don't cover every situation. A much better solution is a set of "R" and "B" decamired (DM) filters. These filters can be used in combination to cover just about every lighting situation where you'll want to warm or cool the image tone - except those scenes lit by fluorescent or non-continuous spectrum light sources.
	Sunlight, skylight, incandescent, and other artificial sources all have varied color characteristics. Because the brain can make adjustments to our perception of color, a white object will still appear white to our eyes in all sorts of lighting, provided only one type of light is used at a time. Color film doesn't have a brain and therefore can't make a judgement call. Film isn't as smart as our brain/eye combination, and will only see an object as being white if it is illuminated by a specific type of light. This is why we have "daylight" film and 2 flavors of "tungsten" film.
	*Color Temperature and MIcro REciprocal Degree*
	All continuous spectrum light sources produce light as a function of temperature, usually expressed in degrees Kelvin (ºK). "Normal" daylight has a color temperature of 5500ºK and "daylight film" is designed for that color temperature. The 2 flavors of tungsten film are 3400º (type A) and 3200º (type B). Photofloods are nominally designed for 3400ºK, but the actually color temperature varies with bulb life (which is short). Quartz lamps used in photo and video fixtures are designed to burn at 3200ºK. If you want to use hot lights, I'd suggest using quartz fixtures as the lamp life is considerably longer and the lamps produce a much more consistent color temperature over their life span. Most tungsten films are type B, balanced for 3200ºK light sources.
	So just what is micro reciprocal degree and why should I care? OK, it's time for some theory and a little math.
	The term mired comes from MIcro REciprocal Degree. The micro reciprocal degree value, or mired value, of any light source is the reciprocal of it's temperature multiplied by 1,000,000. Some examples: "Normal" Daylight = 5500ºK. The reciprocal (1/5500) equals .00018181. Multiply that value by 1,000,000 and we have a mired value of 180 (we can round it to the nearest 10 and dispense with decimal places). "DYS" Quartz lamp = 3200ºK. The reciprocal (1/3200) equals 0.0003125. Multiplied by 1,000,000 equals a mired value of 310. In open shade (a scene lit not by direct light, but by blue sky) or hazy conditions, the color temperature can be much higher (bluer) than 5500ºK. If we measure an open shade scene and find a color temperature of 20000ºK, we would have a scene lit by a mired value of 50 (go ahead, do the math). The decamired value would be the mired value divided by 10, so "normal" daylight would have a DM value of 31, the quartz lamp would have a DM value of 18, and our open shade would have a DM value of 5.
	*What About The Filters?*
	Decamired or DM filters are unique in that they will have a predictable effect by imparting a mired shift of their value, regardless of the light source temperature. Once we know the DM value of our film and our light source, it's a matter of simple arithmetic to determine which filter to use.
	The formula: DM value of the light source - DM value of the film type = DM value of the filter required. Here's the rules: If the DM value of the light source is lower than the DM value of the film, use an "R" series filter. If the DM Value of the light source is higher than the DM value of the film, use a "B" series filter. Example: Quartz lamp at 3200ºK = DM31, Daylight film DM value = DM18, so a DM shift of 13 is required. Since the DM value of the light source is higher than the DM value of the film, we would use a B12 filter. Wait a second... The difference is 13, not 12... What are you trying to pull here?
	OK, you caught me... I forgot to mention the last rule... If the DM value can't be achieved exactly, don't worry. USE THE NEXT LOWEST DM shift value your filters will allow and DON'T EXCEED the required DM shift.
	Remember, decamired filter values are additive. If you're aiming for a DM shift of 5, it's perfectly OK to use a 1½ and a 3 filter together and not worry about the last ½. Also - never use a blue and a red filter in combination. If have your B6 and lost your B3 filter but need B9, don't try to get away with using B12 and R3 - it won't work correctly.

	*More DM Filter Stuff - From Tiffen Data Sheets*
	*"R" Series Filters*
	From left to right: R1½, R3, R6, R12

	*"B" Series Filters*
	From left to right: B1½, B3, B6, B12


	As shown in the table below, it is possible to achieve correct color balance in almost any lighting situation using these 8 filters. This table is from a 1966 Tiffen instruction sheet for DM filters. There is no longer any Type F films being made, but I left the information in to show the versatility of these 8 filters.

	This table is also from the same 1966 Tiffen instruction sheet. The DM values for various films and light sources are listed.

	This table shows the exposure compensation required for all usual combinations of DM filters. Note that B and R series filters are never together used in combination.


	I hope this has been a help and will get you on the road to color correction in-the-camera. By the way, did you notice that I didn't say anything about using DM filters with digital cameras? That's because digital cameras (at least GOOD digital cameras) can adjust their white balance. That gives digital its one big advantage over film - it's adjustability for color conditions. Being a die-hard film shooter, I keep a set of DM filters handy in Series VII and Series VIII. Along with a color temperature meter, they can be real life savers.

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