If you have been taking photos for as long as I have, or longer, you know that before digital cameras, when people talked about filters, they meant some types that aren't used much today. We had blue ones, red ones, and yellow ones. We also had filters for special effects and did things to filters to get our own weird photos.
Back in the day, there was no photo processing software, and really, digital photography was something that people were talking about, but no one was taking it seriously.
With film, using ND filters was hard because you wouldn't be able to tell if your exposures were correct or not until you had the film developed. So, if you had your settings wrong, or forgot to do something, it would be an expensive mistake. Thankfully, with digital you can look at the back and see how your exposure is and then decide if you need more time or less. So, what are ND filters?
Neutral Density Filters
Long exposure photography would not be possible without the use of Neutral Density filters, or ND filters to most of us. If you want that marshmallow effect of a waterfall, you need one of these, well, unless you are somewhere where it is quite dark. If you want to get a cityscape without people, then you can achieve this with one of these. Or if you want that look of the clouds blurring through the sky, then you must use an ND filter.
So, what are they?
They are usually made of glass, and have been made to look very dark, so they allow little light to get through them. This means you have to give your camera a much longer time to allow the light to penetrate the glass to get your image.
They are called neutral because they should not change the colours, or give any colour cast, in your image at all. Cheaper ones will often give your images a magenta hue, which is very hard to get rid of. If you love long exposure photography, it is well worth spending the money on good quality ones. If you look after them, you will have them forever. I use Formatt Hitech ND filters.
Density refers to how many stops or how dark the filters are. The darker the filter, the more stops it has. The most common is a 10 stop, and if you put it up to your eye, you may find that you can only just see through it. If you get a 13 stop, it will be harder and a 16 stop will be almost impossible.
With ND filters you can extend your exposure times so you can take photos on a sunny day, and have your shutter open for 5 or 10 minutes depending on which filter you have. Personally, I'm not sure why you would want to do that, and it isn't something I would encourage as you can end up with some undesirable effects, like hot spots in your images.
Why would you use them?
To get the most out of your filters, there needs to be some movement in the scene you are photographing. There would be no point using the filters if there wasn't any movement to capture. The movement can come from clouds, water or people.
There are many different ways they can be used. So let's look at some of them.
Long Exposure Photography
The most common way is to use ND filters is for long exposure photography. This is where you can take a one or two minute exposure of things around you. What you choose to photograph depends on you. I love doing cityscapes, and hope that the longer exposure will make the people disappear, but have the clouds going through the scene in a blur.
You can set your camera up on your tripod, and then decide how long you want to take your photo for. It depends on what you are trying to do, the environment, and the filter you are using, that usually determine the length of the exposure.
These are not the only way to use ND filters though. I often use them for the ocean to get images showing the waves crashing. It is amazing what you can get with a 1/10th of a second exposure. It's especially good if you don't like that ghostly look that a longer exposure will achieve. A marshmellowy effect with water can look really beautiful.
It is the same with waterfalls. You don't want a really long exposure as the effect can be too much. I often find around 20 seconds gives me a nice soft effect. If you do it for too long, then you might just end up with too much white.
Time Lapses
Another way I've been using the filters in the last year is for time lapses. I try to get a one second exposure for each photo in the sequence, and the best way to get that is to put on either my 6 stop or 10 stop ND filter. It depends on the time of day and the amount of light available. As with all the photography involving ND filters, the more light there is, the more dense the filter you need.
These are some of the different ways to use your filters. I have the 3, 6, 10, 13, 16 and 18 stop filters. I use them all for different things. My favourite one for long exposures is the 13 stop. I probably use it the most.
If you are just starting out, then I would suggest getting a 3, 6 and 10 stop as you can stack them to together to give you the additional 13 and 16 stops. Formatt Hitech has the perfect kit for beginners, it is the Firecrest Long Exposure Kit #1 by Joel Tjintjelaar.
Round or square filters
When you are deciding which filters to use, you have the choice of round filters that screw onto the end of your lens or square ones that fit into the holder that is attached to the lens.
I have always used the second ones; the square filters with the holder. Part of the reason is because I used a DSLR camera, and every time I needed to change my composition I had to remove the filter. It is quicker to remove the holder than to unscrew a filter. There are other reasons too, like if you want to combine filters, you can stack them in the holder.
These days with mirrorless cameras, you don't need to worry about not being able to see through the filter, so I have often wondered if I would be better off getting some round ones, especially for doing time lapses. I was moving my tripod to another spot, and didn't realise I didn't have the holder on properly The filter holder fell off, and I needed a new 10 stop filter. It is the first one I have ever broken, or cracked.
You need to think about what you are going to use them for, which camera and lens combination you have, and how often you will use them. Then you can decide if you want round or square ones.
Problems to be aware of:
There aren't many things to consider, but you can come across problems. They can include movement, wind, or hot weather.
The first one that is a problem here in Australia right now, is summer. With the heat of summer, if you are trying to do long exposures in the direct sun you might find your images will have lots of little spots all over them. These are called hot pixels. There is nothing you can do to stop them, except to change where you are taking photos so you aren't in the direct sun, or try to do your photography early in the morning or late in the day.
Wind is not your friend when it comes to doing long exposures. If your camera keeps moving, then you are not going to get a sharp image. I have two tripods that I can choose between. If I am going out where it is going to be windy I use my large one, Winston by 3 Legged Thing, which is hefty enough to cope with the wind. In the city I usually take Bucky, a more compact tripod, also by 3 Legged Thing.
It is also a good idea to take off camera straps and anything that might swing from the camera that could cause movement. If it is too windy, you might need to lean on your tripod to keep it still. We are always told not to touch the tripod when taking photos, however when it is really windy it can help give it stability. What I might do is put my hands on two of the legs and lean down on them, like I am pushing them into the ground. It's not ideal, but it works.
Speaking of movement, you also have to remember to turn off any vibration or stabilization that the lens might have. You should always do this anyway when you are using your camera on a tripod. The effects of it can ruin your images.
If you are using a DSLR, you need to cover up your eye piece. If you don't, then light can leak through there and leave horrible over exposed areas on your images. It isn't pretty. Thankfully, this isn't an issue with mirrorless cameras.
I could keep going, but I think I've said enough for now. Long exposure photography is a great way to present unique images and give your subject a different look. The filters are expensive, but once you have them, you will have them for a long time. Well, as long as you don't drop them. Good luck experimenting!
