Before you get excited, this is not a post about the type of filters one would use on Instagram or any of the other social media sites. I know, I know, they are marvelous and I also use many of them and have a few favourites as well (Hefe, Lo-fi, X-Pro) but this is actually a post about the lens filters that go on the end of my DSLR lenses. If you are not already using them I am hoping this post will convince you why you should be using them and what the best use for the different filters is.
What are lens filters?
Lens filters are basically a piece of glass that can be screwed on to the front of most camera lenses to perform one of a few functions. On can also find filter holder adapters that can be added to the front of a lens to hold rectangular filters that would not screw on to the front of a round lens. There are also lenses, some that have front diameters too large or not the correct size for a standard filter, that have a slot for a filter on the back of the lens but currently all my lenses have the threads on the front that filters to be added. I know of 4 types, 3 that I have used i.e. Ultra Violet or UV filters, Polarising Filters and Neutral Density (ND) filters and one that I am going to hopefully start using soon in Graduated filters.Each serves a specific purpose but there are also general pros and cons to using lens filters.
Adding a filter to the front of your lens (in addition to the task you choose the filter for) will give you protection from scratches and other damage to the front element of your lens. Now I learned this the hard way when I placed too much importance on the cons and scratched the front element on one of my most coveted lenses, my 70-200mm. I don’t know how I managed to achieve this but I did and only then went out and got myself a UV filter for that lens. The lens filter may also act as a shock absorbing element in the case of a dropped lens or a lens bumped into something that may cause it damage and could protect the lens from more costly damage.
Adding a filter to the front of a lens is adding a piece of glass to the lens that wasn’t intended to be there. If this piece of glass is of poorer quality than the lens itself, the image quality achieved would be reduced. Hence my reluctance initially to add a piece of glass to the 70-200mm. This can be avoided to some extent by not skimping on the filter if you have already spent a fair amount on the lens. A good filter, depending on the size and purpose will most likely cost upwards of R1000 here in South Africa. Adding a piece of glass onto the lens also creates a gap that is filled with air and possibly dust, leading to undesired spots or lens flaring in harsh light. Some of this can be avoided by ensuring both the filter and the lens front element are cleaned regularly. It is also for the reason of possible flaring and reduced light transmission that stacking filters, i.e. using more than one filter at a time on a lens (e.g. a UV and a Polarising Filter) is to be avoided. Stacking filters can also lead to vignetting (dark corners on the photos) on wide angle and ultra-wide angle lenses due to the depth of the stacked filters which can be both desirable or undesirable, depending on the effect the photograph requires.
Ultra-violet or UV filters serve the purpose of cutting out UV light. This was important in the days of film cameras as film could be sensitive to UV light. However with a digital camera this is no longer a concern. So the primary reason most photographers use UV filters today would be to act as protection for the front element of a lens. And as per my scratched lens described above, this is the reason I would recommend using a UV filter as well on all your lenses. One additional piece of advise I have learned is that the UV or any other filter for that matter should be removed for long exposure night shots or night shots with wide open aperture (like when you are shooting the Milky Way – see my previous post) to avoid light reflecting back from the filter onto the sensor causing flares and ghosts.
Now Polarising filters, and in particular the circular polariser I have fitted to the front of my wide angle lens, are my favourite. They are a must for a landscape photographer and I have also seen them used for wildlife photography (something I am hoping to try on my next trip). Polarising filters work in the same way as polarising sunglasses work, allowing light of a particular single direction to pass through the filter. And if you have used polarising sunglasses you will know that the effect is that the colours seem to stand out more, blues are deeper and darker, greens jump out at you and other bright colours seem to almost be neon versions of their own appearance. This is particularly useful to landscape photographer who wants to make the colours in his landscape really vibrant, especially the depth of a bright sky. Polarisers also reduce some of the light passing through the filter, requiring between a one or two stop compensation on light metering compared no filter. This can help when a slower shutter speed is required to show movement in water for instance, however only a little bit.
Polarising filters usually come in the guise of circular polarisers which screws on to the camera lens but have two elements to the screw ring, one that is fixed to the lens and the other that is free to move, allowing the polarised filter glass to be rotated. This allows the filter to be adjusted to the light you are shooting in for the best polarising effect, however this needs to be judged by eye to avoid uneven darker and lighter areas of the photo. Using the circular polariser can therefore take some practice getting used to and I still end up with photos where the circular polariser was not rotated correctly. Lenses where the front element rotates when zooming and focusing (like the 18-55mm kit lens I think) can also be a problem as the polarising filter will need to be adjusted only after focus is achieved. One way to do this would be to focus, switch to manual focus and then adjust the filter. Or to shoot with manual focus from the beginning.
A note for polarising filters: I was advised to always avoid using polarising filters when shooting pictures of people. The marks and blemishes on skin, when shot with a polarising filter, tend to be harshly exaggerated by the polarising filter in some instances. As I use my circular polariser on my wide angle lens, I tend to avoid shooting people’s portraits with it regardless to avoid distorting the image as a wide angle tends to do.
Neutral Density Filters
Neutral Density or ND filters are basically just tinted pieces of glass that allow only a certain amount of light to pass through the filter. ND filters come in circular or rectangular form with a filter holder. Generally they range from 6 to 10 stops of light reduction but can go as high as 16 stops. In layman’s terms this means (if you are shooting with the aperture and ISO set to one value and adjusting shutter speed) that you can allow for longer shutter speeds even in bright lighting conditions. I did a quick check on my camera and if you started at 1/250s, 6 stops (or 18 clicks on the main dial as each stop is divided into thirds) will allow you to increase the shutter speed to 1/4s. 10 stops gets that to a shutter speed of 4s. This allows you to show motion in pictures, producing the effect of silky water and even showing cloud movement in bright light. A practical application would be shooting a waterfall during the day time. An alternate that an ND filter will allow is the adjustment of the aperture setting while keeping the shutter speed and ISO constant. This will mean for example moving from F8 to a more widely open F2.8, dramatically reducing the depth of field of the shot. The practical application of this would be shooting portraits in bright light to get blurred backgrounds or when the flash you are using does not have high speed sync.
Graduated filters or grad filters are like ND filters above but are not uniformly dark, rather transitioning from a dark to clear along the vertical length of the filter. They are generally rectangular and are therefore more likely to require a rectangular filter holder. Grad filters are used to darken out part of the picture while keeping the rest as it appears. Practical application of this would be to reduce the brightness of the sky in a sunset scene for instance while still allowing the foreground to be correctly exposed. The graduated filter and holder generally allow for the filter to be moved up and down, increasing or decreasing the graduated effect by doing so. This is a filter I hope to get my hands on soon and see how it works. However Photoshop does have a graduated filter effect that I can also perhaps try first (I have not had the chance to yet).
So in summary, using lens filters has become almost a must for me. UV filters are almost standard on all my lenses to protect the front element. My circular polariser is of the correct size to be used interchangeably on 4 of my most used lenses but is almost always left on my wide angle lens. ND filters come in handy for certain effects, especially long exposures. And Grad filters I am yet to start using.
Some pictures using the polarising filter