Do I Really Need A Filter?

One question we get asked a lot is what is the advantage of using a filter, compared with just using the camera's manual white balance alone. When you are very shallow, just below the surface, in the top 3m (9ft) then white balance alone is absolutely fine. However, once you are deeper than 3m (9ft) the advantages of a filter become more and more apparent.

The main advatanges of using a filter, as opposed to white balance alone, are more subtle variations of foreground colour, richer blue backgrounds and less noise. The two lemon shark photos, below, were taken on the same dive site in shallow water 3-4m (9-12ft), both these images are shown exactly as taken on my Fuji F50 compact camera:


To some extent both images are acceptable. If you put you hand up to the screen and cover the image on the right and look at the no-filter, manual white balance photo (left) in isolation - it is fine. It is only when you see what a filter adds that you realise the benefits. Filters do much of the work of correcting the colour balance, so the camera's electronics don't have to push and pull the colours so much. This means that small differences in colours are recorded n the foreground. Look at the much more subtle variation of colours on the sand, for example. Also filters attenuate (block) blue light. This makes the background water appear much a darker and richer blue than in non-filtered shots. A deeper depths than this, a photo taken with manual white balance and no-filter will often have grey water.

The same is seen in photos taken with DSLRs. These three photos are all taken of the same wreck in the Red Sea. The left hand image was taken on slide film, which rendered the scene completely blue. The middle image is taken with a digital SLR without a filter, but using manual white balance. The white balance has brought out some of the colour of the wreck, but it has also taken all the blue out of the water behind the wreck, making it almost grey. The right hand image is taken with the same digital camera and lens, but this time using a original Magic Filter. Here the colours of the wreck are brought out and it stands out from the background water, which is also recorded as an accurate blue.


The final problem with making large manual white balance adjustments is that they introduce electronic noise. Using a filter is better because it does most of the work and the electronic processing in the camera does less, so you get less noise. The amount of noise you will get when using manual white balance without a filter will depend on your camera and also your depth. At shallow depths, less than 3m (9ft) the noise will be negliable. Deeper it will increase. DSLR cameras control noise much more than digital compacts. The example below is from a DSLR, if you shoot a compact you can expect the noise to be much worse.

These two photos below show the same subject processed from a RAW file at 16-bit with a standard "blue-look" auto white balance (top) and a manual white balance (below). No filter was used. Viewing them small on the screen the manual white balance clearly reveals come of the colours of the train, although it also sucks the blue out of the water in the background (as we have seen above). However, here I want to focus on when we look at the image in detail. 100% pixel crops are shown on the right of each image. We can see that the strong white balance correction required to correct colours without a filter has introduced lots of noise - seen as a speckled texture. For on screen viewing this noise is not that important as you won't show an image at 100%. But if you want to print your photos, this degradation in image quality obscures the details of the subject and will restrict the size to which you can print.