Review: K&F Black Mist Filter for Astrophotography

Earlier this month, K&F invited me to try out their Black Mist filters as part of my photography work, produce some images, and give an honest appraisal of how well it works.

What is a Black Mist filter?

The K&F Black Mist filter is a type of photographic filter used primarily in filmmaking and photography to create a soft, dreamy, and ethereal look. It is designed to mimic the effects of atmospheric haze or mist, which can add a sense of depth and dimension to images.

The filter works by introducing a subtle diffusion effect that slightly reduces contrast and sharpness while adding a delicate glow or halo around highlights. This softens the overall image, smooths skin tones, and  Portrait and fashion photographers love how the Black Mist filter softens the overall image, smoothes skin and gives a delicate, dream-like look.

The benefits of the Black Mist filter are well established for portrait photography, but I wanted to try it in a completely different genre – astrophotography!

About the filter

The filters come in a variety of strengths and can be supplied as screw in filters with a selection of thread sizes, and as 100x100x2mm square filters which will fit most square filter kits. K&F offer their own filter holder set but if you already invested in one from another manufacturer, their square filters should fit.

Testing the filter

On a clear night near the new moon, I visited Paxton’s Tower – one of my favourite photography haunts – for a night under the stars armed with my camera gear and the K&F Concept Black Mist 1/2 filter to see how the filter performs in some typical astrophotography scenes.

Photographing Venus

One of the attractions of this filter is that it applies an attractive glow to bright points of light. To test this out, I photographed the planet Venus which is one of the brightest celestial objects. It is often called the “Evening Star” or “Morning Star” because it is the brightest planet in the night sky and can often be seen shortly after sunset or before sunrise when other stars and planet are too dim to be visible.

Some ideas for other bright objects you can photograph in the night sky:

• Jupiter is the largest planet in our solar system and is usually one of the brightest objects in the night sky. It has a distinct, steady glow.
• Mars can be quite bright and easily recognizable with its reddish hue. Its brightness varies depending on its position in its orbit, but during its closest approaches to Earth, it can be exceptionally bright.
• Sirius is the brightest star in the night sky and is part of the constellation Canis Major. It appears as a brilliant white star and is visible in the winter months.
• The International Space Station (ISS), when illuminated and passing overhead, can be one of the brightest objects in the night sky. It appears as a moving point of light and can be easily distinguished from other celestial objects.

The difference between the filtered and unfiltered images are obvious. Venus has been given a huge glow. Look to the top right of frame and you’ll see Capella, a star in the constellation Auriga and one of the brightest stars in the night sky, has also been given a pleasing glow. The dimmest stars become even fainter, or don’t appear at all, on the filtered image.

Photographing a constellation

Next, I turn my attention to a constellation. A constellation is a grouping or pattern of stars in the night sky that forms a recognisable shape or figure as seen from Earth. These stars won’t be as bright as Venus, so this is a way to test how the filter performs with prominent stars, the sort you could easily spot with the naked eye.

Cassiopeia is a prominent constellation in the northern sky. It is named after Cassiopeia, a queen in Greek mythology. The constellation is easily recognisable for its five stars that form a distinctive “W” or “M” shape, depending on its position in the sky. Cassiopeia is located in the region of the sky known as the circumpolar zone, which means it is visible all year round for observers in the Northern Hemisphere. It lies between the constellations of Perseus and Camelopardalis.

The difference between the filtered and unfiltered images is more subtle than the previous example, but still you will notice a pleasing glow around the stars forming Cassiopeia’s constellation. 

Most interesting though is the effect it has on the satellite passing through the top of the frame. Much like Venus, this satellite forms a bright point of light in the sky and therefore glows brighter than the unfiltered image. Whether or not this is good news to you is a matter of taste – if you intend to incorporate satellites into your completed image then consider using a filter, but if you prefer your night sky images free of satellites and other orbiting objects, this filter will make your life harder. 

Photographing a star trail

One of my favourite techniques for astrophotography is capturing a star trail – the continuous streaks of light created by the movement of stars across the night sky during a long exposure. Effectively you are capturing the Earth’s rotation in your image, giving your scenes a sense of dynamism and movement.

You can capture star trails by stacking long exposures at a high ISO. Some cameras, such as my Nikon Z7II, allow you to capture up to 900 seconds as a single frame, meaning you can use a low ISO and therefore, very little noise. 

As these images were taken 15 minutes apart the direction of travel for the trails is the same, but the stars will have moved.

This area of sky did not have any exceptionally bright stars during the capture, therefore the primary difference between the filtered and unfiltered images is that the trails are fainter and more diffuse on the filtered image.

Generally this is undesirable for a star trail but there is one important use case where this could be worthwhile.

When stacking star trail images there may be unavoidable gaps in the trail, perhaps while the camera shutter is down or if your camera applies noise reduction between frames. The effect is especially noticeable on telephoto star trails where the motion of stars appears faster. Though you can mitigate against gaps in your trail in-camera, if you find some gaps still appear in your stacked image, then consider a diffusion filter like this to help with the blend.

By creating softer trails with a subtle glow, the “join” between adjacent trails is less easily seen than with sharp trails where the stop and start is more obvious.

Conclusion

There are some caveats to be aware of when using this filter for your astrophotography work. Firstly, there is a small brown colour cast but this can easily be corrected in post-processing. Secondly, you can expect to lose about half a stop of light which is a sacrifice you can afford if shooting with a fast lens, but if using budget or kit lenses the addition of this filter may be a little much.

The filter compares favourably with competing products such as the Kase Starglow and the Tiffen Pro Mist filters. At the time of writing it is the cheapest of the three products and the most readily available – Kase’s Starglow is frequently on backorder and the availability of Tiffen’s filters is hit and miss depending on the thread size. Kase’s Starglow is only available in one strength and as a 100x100x2mm filter, and though Tiffen offers a greater variety of strengths, these are only available as screw-in filters. Therefore I believe it is fair to say K&F’s mist filter offering gives photographers the best choice of fixtures and objectively it is the best priced.

The K&F Concept Black Mist 1/2 filter is an affordable addition to your kit bag if you want to create interesting star glow effects in-camera, which performs comparably to its competitors at a better price point.