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A common problem for photographers is white balance. With so many different light sources such as daylight, tungsten, fluorescent, flash, strobe and countless more, getting accurate white balance can sometimes prove to be fairly tricky. The first problem being is that our eyes are just too well designed and automatically compensate for these different conditions. Our cameras aren’t as clever unfortunately. “What about auto white balance?” I hear you say. Well, yes, this is true to an extent. If you are satisfied with the white balance results you get from switching on to AWB, then perhaps you best not read on. For everyone else as frustrated as me, continue reading!
First of all, lets talk technical just for a brief moment. What is colour temperature? What is a Kelvin reading? Who cares?? Color temperature is a characteristic of visible light that has important applications in lighting for photography. The color temperature of a light source is determined by comparing its chromaticity with that of an ideal black-body radiator. The temperature (measured in Kelvins or K) at which the heated black-body radiator matches the color of the light source is that source’s color temperature; for a black body source, it is directly related to Planck’s law and Wien’s displacement law.
That all make sense? Probably not. To illustrate this a little easier have a look at the following table.
1700 K- Match flame
1850 K – Candle flame
2700–3300 K – Incandescent light bulb (tungsten)
3350 K – Studio “CP” light
3400 K – Studio lamps, photofloods, etc.
4100 K – Moonlight, xenon arc lamp
5000 K – Horizon daylight
5500–6000 K – Typical daylight, Speedlight flash
6500 K – Daylight, overcast
9300 K – Typical CRT computer screen
These values are of course approximate, but gives a broad overview of how much light varies in temperature depending on your light source. Have you ever taken a photo in your living room without a flash and it comes out with a yellow colour cast? Well this is all because your camera thought the colour temperature in the room was different to what it actually was.
Now we have all the technical stuff out the way, what can we do about this problem? Most digital cameras these days will have a handful of preloaded settings to compensate for these different lighting conditions. Let’s go back to your living room, and look around to see where a majority of the light is coming from. Because your first shot came out looking a little yellow, it’s an indication that your light source is a normal light bulb or tungsten. You can set your cameras white balance to the preloaded tungsten setting and you should get a better result. But as you can see in the table above, different light bulbs give off a different Kelvin reading ranging from approximately 2700 – 3300 K. This is big variance if you’re looking to get accurate results.
You can of course shoot with a gray-card to help tell you what your light temperature is, but its a bit fiddly and annoying having to carry a card around with you all the time. They don’t last forever either and easily get damaged and marked which hinders their performance.
I was handed a fantastic little piece of kit called Expodisc. This little device takes all the guesswork and time out of taking a colour temperature reading. You open the box and take out what looks like big fat filter for your lens. I ordered one for a 77mm filter size as most of my lenses are that size and it simply clicks on and off the end of my lens. My 50mm f1.4 has a smaller filter size, so in this case I can simply hold the Expodisc over the front of the lens. You set your camera to record a custom white balance (you may need to refer to your cameras manual for this), place your camera in manual focus mode and with the Expodisc snapped onto the end, stand in the place of your subject and point your camera at your light source, be that a light bulb, a studio flash or the sun! If you have a flash mounted on the hot-shoe, point it at the ceiling or a white wall to give you a reading. Take a shot which will render a colour reading for you custom white balance. Take the Expodisc off your lens and you are ready to shoot with incredibly accurate white balance. It’s quick and easy and makes getting white balance a simple routine rather than a chore or a time consuming job when you come to retouch them on your computer.
It comes with a handy lanyard for whacking around your neck when it’s not in use and a sturdy padded pouch complete with a belt clip if (like me) you don’t like things around your neck. Each Expodisc comes with it’s own individual quality control card which gives its calibration values at time of testing. You also get a quick start card which outlines pretty much what I’ve just taken you through albeit with a bit more detail and there is a CD full of videos and reference manuals conveniently in English, French, German, Japanese, Portuguese and Spanish.
So if you are having trouble with your white balance and are tired of having to colour correct in photoshop or just sick of carrying a grey card around, consider having a look at Expodisc. This will save you bags of time and is incredibly simple to use. I’m not sure why no-one has thought of it before!
ExpoDiscs come in a range of sizes for different lenses – check out some of the range of ExpoDiscs at Amazon.