What’s a White Balance Cap and Why Do I Want to Do This?
There are several different techniques you can use to set the white balance in your camera (and later, in post-processing ). The simplest technique, although rarely the most successful, is to just let the camera automatically set the white balance. The problem, however, is that Automatic White Balance more often than not is Automatic Wrong Balance.
Don’t get us wrong, modern digital cameras are absolute marvels of technology and use brilliant algorithms to manage all manner of things from image compression to exposure, but white balance is a very tricky thing to get just right. As a result, it’s extremely common for photos to have a very slight color cast in the best case scenario, and a horribly obvious color cast when the white balance has been set incorrectly or the automatic algorithm as outright failed.
In place of automatic white balance, you can manually set a white balance either by using one of the presets in the camera (most DSLRs have a wide variety of presets for various lighting conditions) or by setting your own preset using a gray card. The problem with the former is that you’re relying on what the camera’s engineers think the lighting conditions are like and not what the lighting conditions are actually like at that very moment. The problem with the latter is that taking the time to pull out a large gray card, take a shot to set a custom white balance, and pack the card up again is a hassle.
Alternatively, you could include a white card in a few of your early shots during that session and then use the white card as a reference point in post-processing to provide a white balance value for the remaining photos shot under the same conditions. This method is quite effective when done correctly, but it’s both time consuming and expensive (as basic photo editing software doesn’t include the kind of functionality you need to apply a custom white balance value across a whole set of photos). Another issue with this workflow is that just changing the angle the white card is photographed at can significantly change the values it produces in the photo. Using a white card appears quite simple but it actually a tricky skill to get just right.
So if the automatic white balance is suspect, the presets aren’t much better, and setting custom values with a gray and/or white card is a pain, where does that leave us?
It leaves us in the realm of white balance caps which, when used correctly, are the easiest and most fool-proof way to enjoy consistent in-camera white balance and color correction. A white balance cap is lens cover that is fitted with a semi-translucent material that serves as a reference point the camera can use as a neutral color value.
In technical terms, a properly constructed white balance cap will allow light to pass through it onto the camera’s sensor which recreates a perfectly neutral 18% gray (just like the 18% gray reference cards photographers have used for decades). The image above is an actual photograph taken through the white balance cap post in-camera calibration; it shows just how even and neutral gray the light is once the camera operator has used the cap to calibrate the white balance.
The reason the white balance cap is so effective is that instead of trying to calculate the white balance based off of the light bouncing off the subject (which is the case with both the automatic white balance in the camera and using a white card as a reference point in post processing), the white balance cap turns the camera into what is known as an incident meter. Instead of measuring the light bouncing off the subject, you instead measure the light falling onto the subject (the incident light) to determine the temperature of the light itself.
A Look at Commercial and DIY White Balance Caps
White balance caps sound pretty awesome, right? So what’s the catch? The catch is that they can be pretty darn expensive for what amounts to a little camera cap with a piece of plastic in it.
The top of the line white balance cap on the market is the Expodisc and, depending on the size and model type, runs anywhere from $70-120 or so. Then there are low-end knock offs of the Expodisc, most notably the Promaster. which runs around $10-15. In the same price range is the DIY variety, which requires two UV filters and some filler material (two simple UV filters will run you around $10 for most lens setups).
In order to give you the best recommendation, we decided to put these white balance cap options to the test, comparing the in-camera automatic white balance, and the white balance calibration provided by the Expodisc, a Promaster cap, and our own DIY white balance cap under the same conditions in a variety of settings.
What exactly do you get for your money with each of these options? Let’s take a look at the spec sheets, so to speak, of each type of white balance cap.
The Expodisc is a very sturdy machined aluminum cap with a very user-friendly mount system–the rim of the cap has little spring loaded bearings that make it super speedy to snap the cap on and off the threading of your lens without actually having to thread it on or fiddle with any sort of latch. The diffusion material is multi-layered and includes several layers of semi-opaque plastic topped off with a plastic diffuser like you would find in a shop light. The main ring has a lanyard attachment point. The entire thing is hand assembled and calibrated (the calibration/test card is included in the box) in California. You certainly pay a premium for the Expodisc, but it’s a very sturdy and well constructed device. Further, it’s the only white balance cap that is actually laboratory tested and certified to meet any sort of light transmission rating.
The Promaster cap is entirely plastic and consists of one layer of the light diffusion material embedded in a plastic cap that attaches using the sort of push-in tension clips found on a standard lens cap. The plastic is particularly thin and you can actually see the outline of objects through it (in otherwords it doesn’t offer complete and clean light diffusion). It doesn’t feel particularly sturdy and we could see it getting damaged fairly easily if mishandled (but, then again, you can buy 8-10 Promaster caps for the price of one Expodisc).
The DIY cap is pretty darn sturdy, as it’s constructed from two aluminum filter rings and their respective UV glass. You would probably have to throw it on the ground forcefully or step directly on the glass to damage it. The light diffusion material is, as we’ll explain in a moment, whatever material you put between the two sheets of filter glass.
Before we dive into the sample photos, let’s take a closer look at how we constructed the DIY filter:
The DIY cap is a really simple affair. In fact you could DIY by simply holding the light filter material over the lens itself (which is a great way to test materials before taking the time to actually build the finished product). All you need is two identical UV filters, sized for the thread mount on your camera lens.
In the case of our test lens setup, we used two 52mm Tiffen brand UV filters. To turn this filter set into a white balance cap, you’ll need a filler material. There are tutorials galore to be found online recommending everything
from white coffee filter paper to tissue paper to dusk mask filters. Because it’s so cheap to try a variety of materials in DIY cap, we strongly urge you to do so.
To create the DIY cap, simply place one of the UV filters on your material (e.g. the dust mask filter material), trace the filter with a pencil, and then cut it out (staying slightly inside the line made by the filter as the inner diameter of the UV filter is smaller than the outer circle you traced). Then just place your freshly cut out disc inside one of the filters and screw the other one over it, effectively sandwiching the material between the stacked elements like so:
That’s all there is to the DIY cap. Assembling it isn’t tricky, but finding the right material to put inside is definitely a challenge. In our experiments, we found that coffee filter paper was too warm, tissue paper was too cool, and the filter material from a white dust mask (available at any hardware or home improvement store) was very close to neutral with just a tiny hint of coolness. To be honest, we never really found a material we were extremely happy with, so for demonstration purposes we opted to use the dust mask material as it is one of the most widely recommended filler materials.
Now that we’ve taken a look at the price tags and construction of the various white balance caps, let’s go over how to use one and check out the results.
Using Your White Balance Cap
As we mentioned earlier in the guide, the purpose of the white balance cap is to turn your camera into an incident meter that measures the light as it falls onto the subject instead of measuring the light as it bounces off of the subject. In this fashion you are able to calibrate your camera to the temperature of the light itself and not the temperature of the light bouncing off the subject and the surrounding objects.
To achieve this end, you need to actually put the camera where the subject is and point it back to the position you will be shooting from. In other words, if you’re standing on a football field taking a portrait of an athlete leaning against the goal post, you do not take your white balance reading from the 20 yard line looking at the athlete, you walk to where the athlete is standing and meter the light as it falls on him from the direction you intend to take the photo.
Every camera is different, so you’ll need to consult the manual for your specific model, but typically you need to go into the camera settings, look for a white balance entry, and then select custom white balance (as opposed to automatic or a preset like Incandescent). Put the white balance cap on, aim at the location you’ll be shooting from (not the position you’ll be shooting, remember) and take your reference photo. This reference photo will tell the camera what neutral color looks like with the exact lighting conditions you’re working under.
So what does the difference between letting the automatic white balance best-guess and setting a custom white balance using the white balance cap look like? In the photo below you can see a familiar sight, an intersection Stop sign:
These two photos were taken in the late evening on an overcast day. The natural light of was a very warm tone. The photo on the left shows the in-camera white balance. The sign has a blue tint, and the foliage and other background objects seem a bit sterile–that’s not at all what the scene, however simple it was, actually looked like. After popping on the Expodisc and taking a white balance reading, I snapped the second picture. The colors are significantly more true to life and the photo no longer has that sort of sterile blue cast to it.
With a general sense of how the white balance cap functions, let’s take a look at how the different caps stack up against each other under different lighting conditions. If you’ve read any of our other white balance tutorials, you’ll know what comes next; our trusty photography side kick and all around upstanding action figure Spawn is going to lend a hand.
The following photos were taken on a sunny day, in the shade of large tree against a white building:
Under those lighting conditions, the automatic white balance was a bit cool and the Promaster was outright icy cold. The DIYdisc was barely a hair warmer than the camera’s automatic white balance. The only white balance option that actually warmed the image up was the Expodisc. Hands down the most accurate color reproduction in the Spawn-against-the-white-wall test was the Expodisc.
Let’s look at another test. In the following sequence, we photographed a common lily against the green and white backdrop of the lily foliage and the wall:
Again, as with the previous sample, we find that the automatic white balance and the DIYdisc offered similar cool tones. In this setting, however, the Promaster fared much better and came very close to recreating the warm tones of the Expodisc.
As you can see, however, there is a problem with consistency emerging that hinges on the thickness and quality of the filter material. The DIYdisc has a very thick piece of filter material in it and the Expodisc has a several layers of plastic, where as the Promaster is very thin. So thin, in fact, that you can look through it and see the outlines of whatever is in the background (be that buildings, clouds, or the treeline). The Promaster appears to let just enough through that it probably isn’t giving a perfectly consistent read when the camera attempts to meter the neutral color of the incident light.
If you search for DIY Expodisc tutorials, you’ll find dozens of them. Almost every one of them slams the company making the Expodisc for marketing an overpriced piece of crap that anyone could make themselves. We think that judgement is a bit harsh. Yes, you can in fact make your own Expodisc clone, but the process is one of trial and error. If you love saving a buck (or ninety), experimenting with your camera, and the thrill of doing it yourself, by all means build a DIY Expodisc. Be prepared to experiment with quite a few different materials before you find the one you really like (and that offers consistent high quality results). We had to try almost a dozen different materials before we were even kind of happy with the results. As for the other tutorials that suggest holding a fast food napkin or a Pringle can lid over the camera to get a white balance read–that nonsense is for the birds.
Our take on the Expodisc is thus: It’s very sturdy, clearly well engineered, and regardless of what we photographed–flowers, action figures, people, distant buildings, skylines, kids, artwork, etc.–it gave us completely consistent results. Every photo we snapped after calibrating the camera with the Expodisc gave us the same neutral color with just a very slight hint of warmth which was pleasing across landscapes and personal portraits. That’s far more than we could say for the camera’s automatic white balance, our DIY attempt at an Expodisc, or the Expodisc knock off, the Promaster.
So the bottom line is: if you want fast and consistent results, especially if inconsistent results mean you’ll be spending a lot of time working in Photoshop or another post-processing application to fix photos with poor white balance, the Expodisc is a great value.