You might have heard of HOYA's excellent filter quality. I have been using their screw-in filters since the beginning of my photographic journey. In addition to quality, I'm always amazed by their practicability and resistance. Today I'm happy to announce that I'M A HOYA AMBASSADOR. How exciting!

I recently had the opportunity to review the HOYA astrophotography filter STRASACAPE, which aims to reduce the yellow glow from light pollution in night photos.

Filter diameters range from 49mm up to 82mm, and include all the following sizes: 52, 55, 58, 62,67, 72, and 77mm. The filter was delivered in a solid, resistant plastic case which offers no room for the filter to move around. I took the package to the field. I hiked uphill and downhill with the case inside my backpack, and the filter remained intact for the entirety of the trip.

You'll notice the filter's purplish colour when you open the case. This is due to the presence of didymium, an element I will introduce next.

As shown below, the filter's colour difference and light pollution reduction are substantial compared to the photo without the filter. I strongly recommend STARSCAPE and will expand on the various reasons in more detail ahead.  Both images of the sky were taken with the same colour temperature, ISO, f-stop and exposure time. Different settings were used for the foreground.

For reference, all the photos in this review were taken with a Canon EF 16-35mm f/2.8l lens on a Canon 5D Mark IV body. The filter size was 82mm. A Manfrotto 190 Go Carbon Fibre tripod was used when necessary.

Before we dive into the review, as a scientist, I feel the responsibility to introduce you to the issues associated with light pollution and the science behind the HOYA STARSCAPE filter. At the end of the review, I will reveal different actions you can take to help reduce photopollution.

The inappropriate or excessive use of artificial light, also known as light pollution, has been scientifically linked to severe and sometimes deadly effects on ecosystems and wildlife. Many birds, insects and other creatures such as sea turtles use stars and moonlight as guides at night. Artificial lighting leads to dangerous situations and predators and interferes with breeding and migration rituals.

In vertebrates, photopollution also suppresses the production of melatonin - the "sleep hormone" - disrupting circadian rhythms, sleep patterns and affecting human health.

Light pollution also obscures the stars and other celestial bodies, making it challenging for astronomers and astrophotographers to study and capture the wonders of the night sky. As an astrophotographer, I must drive away from metropolitan areas to photograph the stars. But even in the middle of nowhere, I often capture the yellow glow of the nearest city in my photos.

Some of the best places to do astrophotography are Dark Sky Reserves, locations with outstanding stargazing quality. Dark sky status is given by the International Dark-Sky Association (IDA), an organization committed to protecting these areas for public enjoyment and scientific and educational purposes. If you do not have access to a dark sky area, light pollution reduction (LPR) filters come in handy.

LPR filters have been around for a while. They are designed to reduce light of specific wavelengths emitted by street lighting. These glass filters are covered with several layers of coating or made of formulated glass containing chemical elements that absorb particular wavelengths. Instead of several coating layers, the STRASCAPE filter is manufactured with didymium glass.

Didymium (Di) was discovered in 1841 by Carl Mosansder, which believed it was an element at the time. Nowadays is considered a mixture of two rare elements (praseodymium and neodymium). Di is commonly used in safety glasses for flameworking and glassblowing since it protects the eyes from UV and yellowish visible light at 589nm emitted by sodium present in the glass.

Most cities worldwide are saturated with sodium vapour lamps that produce the characteristic yellow light near 589nm. Didymium significantly prevents the lens from "seeing" and capturing this wavelength, as shown in this spectrum. Additionally, the STARSCAPE filter also reduces the light emitted by mercury vapour lamps, another type of gas-discharge lamp frequently used in cities everywhere.

Gas-discharge lamps emit artificial light when electric discharge passes through an ionized gas. They have been frequently used everywhere due to their low price, long lifespan and numerous applications.

It is essential to remind that the effectiveness of any LPR filter will depend on your photography location. The more light polluted the area is, the less effective a filter will be. You can find lessen polluted places in your region with the help of maps like this one: https://www.lightpollutionmap.info.

The main advantage is that the filter will drastically reduce the yellow-green cast from city lights. Your nighttime photos will result in a more natural look. The more accurate the colour profile of the RAW file, the less time the photographer will spend post-processing (e.g., Lightroom, Photoshop, etc.) to correct a colour cast.

In addition to a more realistic colour profile, the images also exhibited increased clarity and contrast. By darkening the sky with the addition of the filter, the stars pop out more against the dark/blue background.

The frame used to mount the filter is also quite important. Two factors must be considered in circular filters: the colour and the thickness of the mount. The "STARSCAPE" has a black and thin rim. Black frames ensure light does not bounce around. Moreover, the filter is mounted in a thin, also known as a "low-profile" frame, compatible with wide lenses. As many of you know, Milky Way photos are often taken with wide or super-wide lenses. Thin frames prevent vignetting in wider lenses, which occurs when the lens "sees" the frame.

Another aspect I love about HOYA is how easy it is to add and remove its filters. When doing astrophotography, a photographer works under low light, sometimes with just a red light headlamp, which creates a challenging working environment. Moreover, the rim also allows you to stack other filters onto this one, like the HOYA SOFTON filters, for example, which enhance further the stars.

Additionally, even though the filter's name is "STARSCAPE", its application is not exclusive to astrophotography. The filter can also be used for cityscape photography to reduce the yellow colour cast of street lamps, highways, monuments and buildings, as seen in the examples below. The resulting night photographs will have a more balanced and realistic colour profile.

All comparison images were taken with the same colour temperature to test the filter's colour change. The same exposure time, f-stop, ISO and post-processing adjustments (except for exposure) were also used when comparing photos side by side. Light pollution filters darken the scene. The exposure of the photos with the filter was slightly adjusted in post-processing to match the exposure of the photos taken without the filter.

Another advantage of using a didymium filter is the fact that it intensifies the warm hues and can, therefore, be used to enhance the contrast and the intensity of colourful sunset and autumn colours without significantly affecting the blues and greens. The HOYA STARSCAPE was previously known as Red Enhancer or Red Intensifier. As exemplified in the sunset image on the left, the filter helped enhance the orange tones.

As demonstrated by the images and comparisons above, this filter delivers what it promises! The resulting photos have no artefacts and are of excellent quality.

Regarding the cons, one thing to consider is that more and more cities are switching to light-emitting diode (LED) street lighting for economic reasons resulting in the shift of orange night glow to a white and blueish hue. This will make light pollution filters less effective.

Another downside, as mentioned before, is that light pollution filters tend to darken images by a couple of stops. Fortunately, this disadvantage can be curved since the photographer can compensate for the loss of brightness by using a tracker or adjusting the ISO or exposure.

In conclusion, I'm delighted with this filter since the advantages far outweigh the abovementioned drawbacks. It is then worth reminding what the pros are:

- easy to add and remove in the field under low light;

- easy to clean;

- delivered in a solid, tight case that makes filter transportation easy and secure;

- no colour shift/vignetting when applied on wide lenses;

- significant reduction of light pollution;

- increased contrast between celestial bodies/Milky Way and the night sky;

- allows stacking of other filters;

- can be successfully used for other types of photography, such as cityscape and landscape photography.

Lastly, check https://hoyafilter.com/ to know more about HOYA STARSCAPE and explore other HOYA filters.

There are a few different ways you can help the cause. Advocate for it whenever you can. Give your time as a volunteer or donate to the IDA. Be involved with your community and local politicians to help create legislation, and improve your outdoor electric lighting by following IDA's Five Principles for Responsible Outdoor Lighting shown below. These include adding motion sensors and dimmers, which can help reduce energy usage and utility costs.

Head to https://www.darksky.org/ to find more about the dark sky movement.