Coloured filters are a commonly suggested solution for the blue or green colour tinge that pictures taken underwater using available light can have. But these filters have their limitations, are not always necessary and can be a double edged sword when shooting pictures or video underwater.
How do filters work?
Where confusion can arise regarding coloured filters is the mistaken belief that they convert light to a different colour. This isn't what happens when light goes through a filter. Instead it is blocking a portion of the light going through it. So in the case of a red filter it is cutting out blue light. The darker red the filter appears the more blue light it is cutting out. By cutting out blue or green light from reaching the camera sensor there will be less of that tint in the image.This means that in shallow water a less dark red filter is more useful as the blue light is less dominant.
When to use a filter?
Filters are most often useful on cameras that don’t have a Custom White Balance system (see my previous blog here) and instead rely on automatic white balance to control colour tone. GoPros in particular have up until the GoPro 6 performed better underwater if fitted with a filter. With the 6 they’ve improved the Auto White Balance to the point where most GoPro experts suggest not using a filter with them.
A filter can also give the Custom White Balance on some cameras a helping hand. If you are shooting jpeg and find that your custom white balance doesn’t perform then perhaps adding a colour filter will improve things.
When not to use a filter?
Because a filter is just removing blue or green light, once you get to a depth where the other colours of light, namely red, orange and yellow are gone you won’t gain anything from using one. This will occur a depth of around 15 to 20 metres. In actual fact having filter at those kind of depths will start to be detrimental because it will block a lot of the light that remains available and your images or video will end up dark and/or your camera will struggle to focus.
Bear in mind also that your distance to the subject counts towards the reduction in colured light reaching your camera sensor. So if you are at 5m depth pointing your camera down at something at 10m then it will be the equivalent of you being next to your subject at 15m. The situation is fairly similar for a subject a distance horizontally from you. There are of course other effects that make it best to always get close to your subject and this is why we recommend using wide angle lenses with conventional cameras (action cameras usually have very wide angle lenses built-in) where possible to allow you to get as close as you can.
If you are using an artificial light source whether it be a constant light or a flash of any sort a filter is unnecessary and will give your images a red or magenta tinge if you use one.
What filter to use?
There are quite a lot of options on the market for colour correction with pros and cons for each.
I’ve used a couple of simple push on domed filters with my old GoPro Hero 3 that worked well. An issue I did find with first one I had, which was a plastic one made by Snake River Prototyping was that it soon got scuffed and scratched and these showed up in my videos. I then changed to a Polar Pro glass filter which has proven more resistant to scratching.
Generally filters for cameras like GoPros can be bought as sets or individually. With the option of an orange filter for shallow water, a red for deeper blue water and a magenta for green water diving. Some manufacturers have produce filters on hinges that can be flipped out of the way when not in use and may have more than one shade of filter useable on the same fitting allowing for easier use when going from shallow to deep water.
Another option on the market are the filter gels that can be placed on the inside of a housing port such as the Magic Filter. These were a pretty popular solution for assisting white balancing in underwater photography with compact cameras when I first started taking pictures underwater. If you are doing shallow dives with just a camera and housing then these can with some cameras improve the colours in your shots. INON produce shaped filter inserts for GoPros of a similar type and function, with three different tones including a red one which they state is for use below 15m. How much deeper than 15m this is useful to is going to depend on weather conditions, visibility etc but the fact that you have the filter inside your housing is a bit limiting when you are above or below its useful depth.
Lastly for colour correction there is what could be called the top of range option from INON, a Variable Red Filter . This uses two polarising filters combined to remove varying amounts green and blue light depending on how they are aligned. This gives extra control over colour tone when shooting with available light underwater but it has a 67mm thread on it so isn’t useable with conventional GoPro housings or similar action camera systems. It is also quite expensive at £179.99.
In addition there are filters available for viewing and taking images of fluorescent marine life. This is a subject all of its own that I may well cover in a future blog.
Hopefully after reading this you’ll have learnt something about how filters work and the options available. I’d conclude by saying that for most action cameras around using the right filter when appropriate is going to improve your images. For cameras with effective custom white balance and/or that shoot in RAW wouldn’t recommend buying a coloured filter. But if you do find that your camera struggles to colour correct on its own then adding a filter may be helpful.
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