We've briefly covered the release of this very special filter before. It blocks out the artificial light of our modern world, light pollution. STC's Astro-Multispectra Filter is designed to block out the orange and green hues from sodium and mercury street lamps. But what's really intriguing for any Nikon full-frame shooter is that this is the first and only option when you shoot wide-angle landscape shots.
Special indeed. This is a so-called clip-in filter that attaches directly to the sensor. Well, sort of. It sits on top of the sensor.
To install the Astro-Multispectra, you have to lock up the mirror. And shooting is only available in Live View, because the filter is in the way of the mirror. That being said, the viewfinder is useless anyway when shooting astro landscapes (nightscapes) or genuine astrophotography. At night, it's just too dark to distinguish features to judge if a composition works or not. So, you will not be giving up the optical viewfinder for the filter, but for the genre.
Here's how what to expect from the results when you compare shots taken with and without the Astro-Multispectra Filter:
So, how does it work? Well, light comes in different shapes and energies. What we perceive as colors are actually different frequencies of visible light. Different sources are responsible for different colors. And since our night is illuminated by mostly sodium and mercury streetlamps, we can very effectively block out those colors when we photograph the night sky.It makes sense that camera sensors are designed to pick up on the frequencies that are visible to the human eye to make representations of the natural world. There are even specialized cameras that are more sensitive to a particular frequency. Take for example the Canon 60Da and the Nikon D810a, which are designed to be more sensitive to the reds of Hα emissions often found in deep space objects like nebulae. Those cameras are of course marketed towards astrophotographers, but you can actually convert your own camera to be more sensitive to any color than others, even those we don't see with our own eyes like near-infrared and ultra violet. But since the frequencies of the latter two lie very far apart in the spectrum, it's hard for lens manufacturers to focus all of those colors in the same spot. Even the far ends of the visible spectrum, red and violet, break differently when they travel through multiple layers of optical glass. If the colors do not align when they've passed all the elements in a lens, unsightly lens aberrations will be captured in your images. This brings us to why you should be using a clip-in filter when shooting the night sky with a wide-angle lens. The more extreme the angle of the incoming colors, the more you will notice these lens aberrations. The benefit of a filter behind the lens is that the light has already been gathered in the right spot (the sensor). But you can also use this clip-in filter with more than one lens, whether your glass has a filter thread or not.
Dark Skies and LED
You can of course head over to the more rural or protected areas to avoid light pollution altogether. There are many more interesting foreground subjects in those locations anyway. So, it begs the question of necessity of light pollution filters. Are we getting too lazy to go to the nearest dark sky site?
Well, we are rapidly losing the night sky. Earth is rapidly becoming more and more overpopulated, and our activity never ceases, even at night. That's much to the detriment of the natural world, since many species of animals and even plants cannot cope with artificial lighting. Luckily, there are alternatives to lighting our nights with high-pressure sodium vapor lamps, like LED lights. But those can be even brighter, and the jury is still out if LED is a good replacement if we strictly look at its effects on affected flora and fauna. LEDs are also more blue and produce a wider emission line than sodium or mercury lamps, so taking pictures around LED street lamps with one of these filters may not be a good idea.
LED lighting will eventually replace most of the artificial light around the globe. From an energy-saving perspective, that's a good thing. But how long will this $185-filter be useful?
We will be reviewing the use and quality of the filter when it arrives in multiple scenarios. In the mean time, what would you like to see me photograph with this filter?