NiSi 100mm Star Soft Astrophotography Filter

They are available in many different densities, ranging from 2 to 20 stops, but the most popular are 3-, 6- and 10-stops.

3-Stop | 0.9 - This filter is used to add a slight blur to water before the sun has set or after it has risen. At f/16 and ISO100, it is impossible to achieve a slow enough shutterspeed to get the ideal amount of blur in the waves while the sun is up. Three stops of darkening will normally allow a shutterspeed of 1/10s to 1/2s during this golden sunlight phase, producing soft lines in the waves.

6-Stop | 1.8 - This filter serves the same purpose as the 10-stop, but it is better suited for sunset and sunrise. When the sun is close to setting or rising, a 10-stop ND will require a very long shutterspeed at f/11-16 and ISO100 to produce the correct exposure - often as much as 5-10 minutes. A 6-stop ND is thus much more suited for capturing long exposures of 30-60s around sunset and sunrise.

10-Stop | 3.0 - This filter is used primarily for blurring the sea to a flat mist and for blurring clouds into abstract lines. It can also be used to remove traffic and people from urban scenes by blurring the moving elements. At f/11-16 and ISO100, it usually produces a shutterspeed of 20-30s in early morning or late afternoon with strong sunlight.

15-Stop | 4.5 - This filter is serious long exposure territory and will produce exposures times of 1-4 minutes in peak daylight and 5-30 minutes during golden hour.

When the dark part is positioned over the sky of an image, it ‘reduces’ the amount of light allowed through that part of the frame and this results in a darkened exposure of the sky. On the left side of the image it shows the result without any filter and on the right it shows the result with the filter. Graduated Filters have two variables - the graduation type and the density. Read below to find out more.

These filters are typically for scenes with a very dynamic horizon, like landscapes with trees or high mountains. Soft grads are the most forgiving and easiest for beginners to use.

Hard Grad - These filters are typically for scenes with a straight and uniform horizon, like the sea. If a hard grad is not positioned perfectly, it will be clearly noticeable in the image as a dark line below the horizon or a bright line above it. We advise that beginners stick to soft and medium grads.

Medium Grad – Medium grads are a newer product that most manufacturers only released in 2016/2017. Many photographers often found hard grads too hard and soft grads too soft and thus it was obvious that something in between was necessary. It is also the perfect solution for photographers that don’t want to commit to a hard or soft grad. Not everyone can afford to buy the full range of these filters and the medium grads are an excellent new compromise.

Reverse Grad – These filters serve a very niche, but useful purpose. When shooting into a bright sunset/sunrise, the brightest area is right on the horizon and then the sky darkens towards the top. When using a normal graduated ND, it will result in a correctly exposed horizon, but the top part of the sky will be far too dark. A Reverse Grad also has a clear lower half, but it is darkest in the middle and then gets lighter towards the top. This allows one to more accurately balance those exposures that are brightest on the horizon.

Focal Length Factor - A longer focal length softens the graduation as the image is captured through a smaller portion of the filter. If you shoot a lot of landscapes with your 24-70 or 70-200, then you'll need hard grads.

The most popular densities are 0.6 and 0.9, but a 1.2 is becoming increasingly popular.

1. 0.3 (1-stop) is for experienced shooters, usually to be combined with a 0.6 or 0.9.

2. 0.6 (2-stop) is the most popular filter as a 2-stop difference between land and sky is most common. If you shoot a sunset/sunrise the 0.6 will be the all-rounder that best balances exposure between land and sky in most directions.

3. 0.9 (3-stop) is the ideal if you like shooting into the sunset as the 0.6 isn’t always dark enough for into-the-sun shots. The issue with the 0.9 is that it will be too dark if shooting 90-degrees from the sun or with the sun at your back.

4. 1.2 (4-stop) is for shooting directly into a very bright sunset/sunrise.