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You are hereHome > Articles > Capture Accurate Colour with the ExpoDisc

Capture Accurate Colour with the ExpoDisc

The White Balance (WB) feature of a digital camera is seldom used by beginners, often used by advanced photographers when taking pictures in artificial lighting, and often frustrating to set correctly in difficult real-world situations when relying on a white or grey card.

The ExpoDisc filter from Expo Imaging provides a simple solution to consistently obtain accurate colours. If you take lots of pictures under artificial lighting that need to have accurate colours, you may want to save yourself lots of post processing time and check out the ExpoDisc. It is one of those simple and elegant ideas that makes you wonder why it was not invented earlier.

 

If you have ever asked the question on a forum board posting why your interior pictures under artificial lighting come out with funny colours, chances are that more knowledgeable photographers would have advised you to use a different White Balance setting: e.g. 'Fluorescent WB' when taking pictures in a setting that is mostly lighted with fluorescent lighting, 'Incandescent (or Tungsten) WB' at home (if you are using incandescent light bulb), etc.

But mention 'White Balance' and beginners' eyes start to glaze over. The subject can be difficult to understand and when beginners try to use it, they rarely obtain consistently good results. Many don't even bother and just accept the weird colour tints in their pictures.

But you don't need to understand WB to use it expertly (just as you don't need to understand how an engine works to drive a car expertly). All you need to understand is that each colour of light has a colour temperature and when you set WB on your digital camera, all you are doing is telling it what the colour temperature of the prevailing light (or more technically correct, what the colour temperature of a white/grey card under the prevailing light) is. A white/grey card illuminated by natural sunlight has a colour temperature; has a different colour temperature when illuminated by fluorescent light; a different one when illuminated by incandescent bulbs, etc.

Manufacturers set your digital cameras to default to daylight (or sunny) WB. For taking pictures under artificial light, they usually provide corresponding WB settings for Fluorescent, Incandescent, etc. Though those WB settings sometimes are accurate enough for most general picture taking, there are times when you want to capture totally accurate colours.

To be able to do this, certain digital cameras (usually the more advanced ones) provide a Manual / Custom / Pre-set WB function that allows you to measure the colour temperature and set it for your digital camera.

The thing is that to manually set WB, you need to let your digital camera measure the colour temperature of a grey or white card (since no 'white' card is truly white, it can pass for the '18% grey' that a digital camera ideally needs). By manually setting the WB, you are telling the camera what the colour temperature of a white/grey card is under the prevailing lighting. The camera then computes the difference (between the colour temperature of a white/grey card under natural light and under the prevailing artificial lighting) and shifts all the other colours accordingly by this difference.

Having a white/grey card handy is the problem for most of us. At home, surely there is printer paper available but not so if you are on location away from home. A good solution is to have a laminated white/grey card that you can carry with you at all times. Better still is to have a white/grey filter that you fit over your camera lens. The ExpoDisc is such a 'filter' that will fit over your camera's lens and help to provide consistently accurate colours.

INSTALLATIION & USE

The ExpoDisc has two sides: a plain white side and a side criss crossed with lenticular lenses which diffuse the light so as to yield an 18% grey. The white side goes against your camera's lens. That's all there is to the installation.

ExpoDisc on Camera

You would normally buy an ExpoDisc with a diameter equivalent to the filter size that fits your largest lens. A larger filter size can be used on smaller lenses by simply holding the ExpoDisc over the end of the smaller lens.

For this review, we used the Fujifilm FinePix F30 (in case you thought the ExpoDisc is only for pros using DSLRs) and simply held the ExpoDisc against the lens.

ExpoDisc on Fujifilm F30
Fujifilm FinePix F30 with ExpoDisc filter held over the lens
to set Custom WB

To get an accurate WB measurement, the light illuminating your subject needs to pass through the ExpoDisc.

With the ExpoDisc placed in front of your lens, point it in the direction of the direct and reflected light. Ideally, you want to stand where your subject is and point the camera back toward the main light source (ambient, studio or flash -- but not the Sun, where there may be a risk of damaging your image sensor). When it is not possible (or even desirable) to stand where your subject is, you can stand under similar lighting and point toward the main light source.

If you use P, A or S mode, just press the shutter release button to set manual WB correctly. In M mode, you need to ensure that the exposure is metered properly before pressing the shutter release button.

Interestingly, in M mode, the ExpoDisc turns your camera's light meter into an incident light meter, i.e. you measure the light falling (incident) on your subject instead of the light reflected from your subject and you can use the exposure you've set to actually take a correctly exposed picture with accurate colours.

TESTS

It can sometimes be quite a pain to try to set WB manually using a white sheet of paper and results can often be very inconsistent. Some cameras are easier to set manual WB on than others, requiring many tries for a satisfactory reading. Can the ExpoDisc give me accurate colours with just one WB measurement?

To find out, I decided to test the ExpoDisc (neutral version -- the 'portrait' version is calibrated for portraits) using our regular test WB shot. To the white sheets of printer paper, I added some colours, especially red, dark blue and yellow.

I take 5 shots:

  1. Taken with Auto WB
  2. Taken with WB = Incandescent
  3. Taken with Custom WB set using a White Sheet of Paper (reflected light)
  4. Taken with Custom WB set using ExpoDisc (incident light)
  5. Just for fun, I take a 5th shot with Custom WB set using ExpoDisc (reflected light)

You can see and compare the results below for yourself:

WB Comparison
Auto WB
Incandescent
AWB
WB=Incandescent
Custom WB using White Sheet of Paper (Reflected)
Custom WB using ExpoDisc (Incident)
Custom WB using White Sheet of Paper (Reflected)
Custom WB using ExpoDisc (Incident)

 

Setting Custom WB usig ExpoDisc - Reflected vs. Incident
Custom WB using White Sheet of Paper (Reflected)
Custom WB using ExpoDisc (Reflected)
Custom WB using White Sheet of Paper (Reflected)
Custom WB using ExpoDisc (Reflected)
Custom WB using ExpoDisc (Incident)
Custom WB using ExpoDisc (Reflected)
Custom WB using ExpoDisc (Incident)
Custom WB using ExpoDisc (Reflected)

And here are a couple of sample shots in the field:

AWB
ExpoDisc

AWB
Mixed Lighting: Incandescent + Natural Light

ExpoDisc
Mixed Lighting: Incandescent + Natural Light
Auto WB
ExpoDisc
AWB
Mixed Lighting: Fluorescent + Natural Light
ExpoDisc
Mixed Lighting: Fluorescent + Natural Light
Since the light is ambient and similar all round, I did not walk to the clock tower to take an incident reading; I just pointed the camera with ExpoDisc at the tower and set Custom WB.

VERDICT

Setting WB using the ExpoDisc and incident light yields the most accurate colours.

Note that in shot #5, when I set Custom WB using the ExpoDisc and reflected light, I cannot place the ExpoDisc against the lens. In this case, I am simply using it in lieu of a white sheet of paper and so need to angle it to obtain the reflected light.

The ExpoDisc is certainly handy to have around and since it works extremely well, it makes setting manual white balance a snap, increasing the likelihood you'll do it more often -- thus reducing the need for post-capture color adjustments whether you're shooting in RAW, TIFF, or JPEG.

The ExpoDisc does not come cheap. If you take the occasional indoors pictures and don't mind some post processing the odd picture, there are many alternatives that work on the same principle of diffusing the light (use a white sheet of paper, your white shirt, make your own diffuser -- or simply shoot in RAW and adjust in post processing).

The ExpoDisc is most useful for photographers who:

  • take lots of pictures primarily under artificial lighting
  • need to capture accurate colours, and
  • prefer not to bother with post processing

Photographers who capture images in the RAW format (which allows the WB to be set in post processing) may also benefit from using the ExpoDisc. Sure, you can always post process in RAW, but it is so simple to get it correct right from the start by just spending a couple of seconds to set Custom WB with the ExpoDisc. With no WB post processing required, and especially if a fine JPEG image is also captured with the RAW, the ExpoDisc can quickly pay for itself in time saved.

Disclosure: This unbiased review is based on an ExpoDisc filter provided by the manufacturer, and which we were allowed to keep.

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Related Links:

- Expo Imaging
- ExpoDisc
- PhotoGallery




 

 

 

 

 



 

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