7/30/2023 0 Comments Astronomik uhc agena astroI think the Astronomik filter (8+ years old) shows red/blue fringing and I’ll check next time I’m observing. I have seen this in a filter and I much prefer the Tele Vue solution which gave mildly green stars of uniform colour. When Tele Vue first introduced their original Bandmate Nebustar (UHC equivalent) they made a point of showing how their filter didn’t produce red/blue fringing around stars like a competitors filter did. I think what Don said about it being impossible was a filter that produced white stars and not referring to what you see. The 2" size is more universal-it fits 2" eyepieces, the bottom of most 2" to 1.25" adapters, and 2" star diagonals in compound scopes. The nebula filters won't help reflection nebulae like those in the Pleaides or M78 in Orion.ĥ. Make sure the nebula is an emission-type nebula. It could lose a whopping 2.5-3.0 magnitudes at the horizon!! So try to view the nebula when it is near or crossing the imaginary N-S meridian.Ĥ. Your nebula target would lose ~0.25-0.3 magnitudes of brightness at the zenith, and double that at 30°. Make sure the object you're looking at is at least 30° above the horizon. at least 30 minutes after turning off all lights.ģ. That means 30-45 minutes outside, away from all lights, i.e. Make sure you are as dark-adapted as possible. So, what can you do to maximize the experience?ġ. There is a little contrast enhancement, just not enough to make a large difference. So since only 22-23nm of bandwidth is necessary for maximum contrast, the extra bandwidth just lets a bit too much light pollution through (why it only works best in a truly dark sky). Most of today's higher-quality UHC type narrowband filters are in the 22-27nm bandwidth range, like Astronomik, TeleVue, DGM, Lumicon, ICS.Ĥ5-50nm is very common among the Chinese UHC-type filters, so you want to avoid these if you can. To achieve that, a bandwidth in the filter that just passes the light of the nebula is ideal.īut there are always slight irregularities in the production of filters, and they react differently to short f/ratios like f/4 or faster, so the bandwidth needs to be about 8nm wider than the minimum possible bandwidth of 14.6nm (the spacing between the H-ß line and the O-III lines) The more of the extraneous light suppressed, the darker the background behind the nebula and the more contrast there is between nebula and sky. Nebulae emit light in discrete wavelengths and any other light passing the filter is extraneous to seeing the nebula. Recommended only if you can test the individual filter: I bought 1.25” filters of various makes and types and then bought 2” versions of the ones I liked most. Use the filter size to match the eyepiece barrel size. Reason being one day you’ll forget there’s a filter in your adaptor and put a 1.25” Barlow straight through it. Some users will suggest you get only the 2” version and a 2”-1.25” threaded adaptor I won’t recommend this and neither does Tele Vue and that is why their adapters are not threaded. I’m not sure what eyepieces you have but you can start with a 1.25” version to test under your conditions and then later get the 2” version if you like it. I understand the new Lumicon O-III Gen 3 and newer Tele Vue (Astronomik) filters are very good based on reviews online but until I get these I cannot comment further. My recommendation is based on use of the above through various telescopes but mainly a 10.1” f6.4 Newtonian. I do like the very natural look of the earlier Tele Vue O-III but my preference for a pure O-III line filter is for the Lumicon O-III. I have all of these but the earlier Tele Vue not the latest Astronomik version. Thousand Oaks is good too but transmission is a little lower at least on the sample I have so I think it is better on a larger aperture telescope (background is jet black though in 10.1” giving very high contrast!). I also recommend the Lumicon O-III but you cannot go wrong with Astronomik or Tele Vue. The O-III is best all round line filter for most nebulae. The UHC is a good choice as it passes O-III and H-Beta but given your sky pollution I recommend the O-III for greater contrast. You will see a significant contrast boost especially with a narrower bandpass line filter such as an O-III under polluted skies.
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