Neutral density (ND) filters are a landscape or outdoor photographer’s best friend. They let you control light exposure, so you can widen your aperture in bright light or slow down shutter speeds to create blur motion in objects such as water. When it comes to choosing ND filters, you’ve got different options at your disposable, including fixed ND filters and variable ND filters. But, should you opt for a fixed ND filter or a variable ND filter?
Whether you choose a fixed ND filter or a variable ND filter depends on what suits you best, and the type of images you capture. Both offer great benefits to the photographer, so there’s no right or wrong answer. However, there are certain scenarios where you may prefer one filter type over the other.
ND filters restrict light entering a camera lens according to different stops of light. A small f-stop, such as f-stop 2, lets in more light to your camera compared to a large f-stop, such as f-stop 10.
A fixed ND filter covers a single f-stop of light exposure, whereas a variable ND filter covers a range of light exposures, typically from around 2-8 f-stops, although this can vary.
By rotating the front element of a variable ND filter you can select and change the amount of light exposure you want, with just the one filter. If you want to switch light exposure up or down using a fixed ND filter, you’ll need to physically remove the filter and replace it with the appropriate type.
Variable ND filters, therefore, offer great convenience for photographers who work with changing light conditions, when you need to shoot fast of if you want to experiment.
Fixed types, on the other hand, are preferable for photographers who tend to stick to the same level of light exposure or shoot in slow conditions where you can take your time to set up a shot or change filters if you need to. Plus, you can stack them, but be aware of vignetting.
If you don’t move around with your photography, such as working from a studio, you can probably afford the space to keep several fixed ND filters in your camera kit, so you might not need a variable type, which is also more expensive. On the other hand, if you’re out and about a lot when shooting, having a single variable ND filter compared to lots of separate fixed types saves having to carry them.
If you shoot videos, a variable ND filter is advantageous to keep shutter speeds slow and constant, which can be hard to achieve in light that is bright but constantly changing.
One thing to be careful of when using variable ND filters, especially with a wide-angle lens, is that when you push the filter past a density of around 8 f-stops, an X mark appears on your image. Some cheaper makes can also produce an unwanted colour cast.