I bought the Orion Ultrablock light-pollution reduction filter and received it recently. It is a tiny little thing, but that shouldn’t have surprised me, because my Orion variable density moon filter is also very small.
There are four main types of filters that are available to the amateur astronomer. What they do is to selectively remove certain wavelengths of light from being transmitted through the eyepiece to the eye. They don’t make anything brighter; in fact,they all tend to make the objects dimmer, either by just a little or a lot. But their purpose in removing the wavelengths is to enhance the contrast between what is being transmitted and what is being blocked. The sky surrounding an object appears blacker, so that the transmitted light coming through the filter from the object shows a greater range of contrast.
Two filters are for viewing only very selected narrow wavelengths of light: these are called line filters – the Oxygen III band, and the Hydrogen Beta band. In other words, they cut out all light except for one or two extremely narrow bands, which the filter allows through. These two types of filters are only useful on certain types of objects that emit light in those bands – certain types of nebula. They are very specialized to only certain handfuls of objects, most of which are far too dim to see from light-polluted Manhattan. But they are supposed to work very well on them.
Then there are the light-pollution reduction (LPR) filters – the broadband and the narrowband types. The broadband type works to eliminate light pollution that is emitted from certain types of outdoor night lighting, called mercury vapor and high-pressure sodium lights, that are used as streetlights, or in parking lots, places like that. You’ve seen these lights: the mercury kind is the light that emits the bluish glow, and the sodium kind emits a yellowish light. The broadband filter passes through all wavelengths of light except for two narrow notches precisely where these two types of lights emit their light.
The narrowband LPR filter is like the broadband LPR filter on steroids, rejecting not only the mercury and sodium lamps, but incandescent lighting as well, and it fully, or almost fully, suppresses these light-pollution sources. The narrowband LPR does a more effective job of eliminating all sources of light-pollution than the broadband LPR, and producing even greater contrast between the sky and the object you’re observing.
Or at least, that’s what I’ve read. This Orion Ultrablock LPR filter is the first filter I’ve ever owned (not counting the moon filter, which kinda doesn’t really count too much anyway), so I’m not speaking from experience here.
The filter arrived, and under the stars we went. Or at least the high cirrus clouds. I looked at Jupiter with it for a quick second – and the planet turned an unattractive shade of green. Then I swung around to my all-time favorite deep sky object, the Great Orion Nebula (M42). And for the first time in my life, I think I saw M43, which is M42’s neighbor.
There’s absolutely no question about the effectiveness of this filter – it works great. The sky went black, and the nebula popped into view. Not that I couldn’t see it without the filter, but it really just popped. The contrast was superb. I could see more tendrils, more dust lanes. Oh, how I’d love to get my scope out to a dark site to really see some things! But using this filter is definitely gonna suffice for now. And a little ways removed from the main nebula, there was some nebulosity around another star in the field of view, a star that I’d never seen nebulosity around before. Could this be M43? Checking the star charts, I think it was.
I had wanted to try to use the filter to see M1, The Crab Nebula, for the first time. But as I mentioned, there were already some high cirrus-y clouds that were probably limiting the lowest magnitude I could see, and M1 is relatively dim for me at 8th magnitude anyway. Later that night, the clouds really rolled in solid and prevented any further observing. But this filter is supposed to work great on M1, so I’ll definitely be giving it another shot.
At least I can say that the Ultrablock is an unqualified success in terms of M42, which has always been my favorite deep sky object, ever since I was a teenager. I will be using it on other objects as well once the skies clear – and it gets out of the frigid teens. Brrrr!
Meanwhile, I’ve also read some great stuff about another filter, the Baader Moon & Skyglow filter. Although I thought that it was just another broadband LPR filter, and thus similar to but weaker than the Ultrablock, others at Cloudy Nights have been saying that the M&SG is effective on the planets and the moon – and works better than a standard neutral density moon filter, like the one I have. Since the moon and planets are my very favorite objects, I will be keeping my eyes open for a deal on any used M&SG filters that may come up.
Next time – the Luminos 10mm ultra-wide field eyepiece.