An Achromatic Refractor's Best Friend
Saturday, 14 September 2019 | Steven
I very recently bought a barely used Sky-Watcher StarTravel 120 achromatic refractor, which has a focal ratio of f5, and is naturally prone to chromatic aberration, giving some objects a purple outline, and even horribly discolouring stars at times, especially if your stock star diagonal is pretty cheap.
I upgraded to a wonderful William Optics Amici prism diagonal which helped a lot, but this little filter is an absolute gem.
Chromatic aberration is very noticeably reduced, and it certainly makes a difference in filtering out light pollution, and reducing the deleterious effect of a bright moon in the sky.
Colours look very natural, and you get none of the overall yellowy colour that various other light pollution filters can produce. The change in colours is so subtle that you just don't notice it, with a dark looking sky looking black as it should.
It is wonderful to get a filter that meets a dual purpose with distinction. If you have an achromatic refractor, do yourself a favour and get one of these, and upgrade your star diagonal if you haven't already if you got a relatively budget refractor. Your views will be markedly better, especially if you have a shorter focal length telescope.
Can't recommend this filter enough. It won't turn your refractor into performing like a high-end and very expensive apochromatic refractor at very high magnifications, but it will help you get the best out of your optics and help reduce the effects of light pollution into the bargain. Fantastic product.
Friday, 11 April 2014 | Nick
Absolutely super filter, really does away with ca and sharpens up fine contrast in planets and lunar views. So very pleased with results, makes double star splits a pleasure. I can really recommend this for achromatic refractors.