Neutral density filters
These are probably the most popular effects filters used by landscape photographers at the moment and are loved and loathed in equal measure. If you look at a site like 500px.com and check out the most popular images, the landscapes making the top of the list are all heavily filtered to give a dramatic look to the sky or slow down the exposure for a misty ethereal sea.
I’m going to show my hand early here – I’m
an ND filter user (saying it makes me feel kinda dirty). I like the options they offer for creative experimentation and
I’m in the fan camp when it comes to the long exposure images – I think they
give the opportunity to introduce “Mood” to an image and convey more of a feel
for the location. For every fan of these images however, there are just as many who
really don’t like them.
I recently read a magazine article where a photographer laid out his case against the use of ND filters, saying that he’d seen enough “pink skies and milky seas” and that we should stop using filters as “Ansel Adams didn’t use them, so they’re basically a superfluous visual trend”. I have a colleague who falls into this camp, saying that you can adjust the exposure of your skies in photoshop, so why put a piece of Perspex in front of an expensive lens? I think he has a point, but in reply I think, not everyone has his level of photoshop skill to correct their images in processing and many prefer to get their exposure right in-camera to start with.
Whichever side of the fence you fall down on, here’s a quick rundown on what these filters can offer and where to use them.
Neutral Density (ND) filters are basically used to alter the amount of light that enters the front of your lens – think of them as sunglasses for your lens. They’re called Neutral Density because they are designed to lower the light entering the lens without adding any detrimental colour cast to your image – hence “Neutral”. In practice – many do alter the colour, especially the cheaper non branded versions, so this is something to bear in mind when buying.
There are 2 basic types of Neutral Density (ND) filter – Solid filters and graduate filters. Almost all ND filters are manufactured from resin sheets and are then usually dyed by hand to the amount needed for a specific strength of filter. There are some glass versions but most manufacturers now use optical resin as it's much safer. The down side to this is they can scratch really easily, and so need to be handled carefully and stored well to keep them in good condition. The graduated filters are dip dyed by hand to get the graduated effect. It's part science - part craft.
How many times have you shot an image outdoors only to find that your exposure either blows out the sky or makes the foreground too dark? This is due to the dynamic range of the light in your image being far greater that your camera sensor can capture. It will be able to properly expose for the sky or the ground but the stretch between the two is too much for it to cover. Ordinarily, the way to compensate for this is to take a few bracketed exposures so you get a good image for both sky and ground and then combine these with image editing software to make a better exposed single image – this is a simplistic form of HDR image (High Dynamic Range).
If you want to improve your image in-camera then this is where an ND grad can help. It will allow you to reduce the brightness of the sky so the foreground can now appear lighter – giving a more balanced overall exposure. As an added bonus effect, a grad filter can throw more definition into the sky, adding more drama to clouds. There are 2 typed of graduated ND filter generally available – hard or soft grad. The difference is obvious when they are put side by side with the hard grad tapering off very quickly to clear and the soft grad having a more gentle graduation to clear. I’ll look at these in more detail in the next posting.
These are used more as a creative effect filter, where you reduce the overall light entering the lens, to enable a longer exposure time during daylight hours. This will allow you to blur moving objects while leaving fixed objects pin sharp, so this is the filter you want for that image of a jetty sticking out into a sea of fog.
In the main – solid ND grads are the filters that you either love or hate and the one that divides opinion the most. I like them and they are great fun experimenting with – I can see this kind of image falling out of favour sooner rather than later as tastes change and the next big thing catches people’s imagination. They’re really great for moving water, so ideal for rocky streams where the water movement can be altered creatively. Also, you can use them for architectural images where there are a lot of crowds – make the exposure long enough and the people will drop out leaving just the building, of maybe a couple of interesting ghosted figures – all great fun to work with!
I’m going to do a post on each of the 2 types of ND filters in more detail as there’s a lot of ground to cover, but before winding this up, I’ll give an overview of how ND filters are calibrated, and what the figures mean.
How are they calibrated?
When looking to buy any Neutral density filters, they will have some kind of calibration system to let you know how dark they are. This is where a lot of confusion arises as there are 2 ways that manufacturers list their product and it’s confusing if you’re unfamiliar with them. ND filters are either calibrated with a number or by the number of f/stops of light they reduce the exposure by. The 2 systems do match up:
2 stop ND = ND 4
3 stop ND = ND84 stop ND = ND16
5 stop ND = ND32
6 stop ND = ND64
7 stop ND = ND128
8 stop ND = ND256
9 stop ND = ND512
10 stop ND = ND1024
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