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Lumicon UHC, Astronomik UHC

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#1 Michael Rapp

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Posted 10 December 2012 - 04:28 PM

Hi all,

I have an Astronomik UHC filter (not the UHC-E, but the actual UHC) that I used for imaging and that I am now repurposing for visual use. (I haven't actually used it for visual yet.)

I am wondering if there is any advantage to the Lumicon UHC over my current Astronomik UHC.

I pulled up Christian Buil's filter curves page at http://www.astrosurf...ters/curves.htm and looked at the plots for the two filters and restricted my attention to 4000-7000 A, which is the range for human vision.

The Astronomik is a little tighter around the OIII lines, but the big difference is that the Astronomik lets in the the Ha and SII lines, whereas the Lumincon does not. Am I remembering correctly that human vision cannot detect the Ha and SII emission lines?

My interpretation is that for visual use, I'm probably fine keeping the Astronomik UHC and don't need to rush out and replace it with a Lumicon.

#2 Scott in NC

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Posted 10 December 2012 - 07:21 PM

Hi Michael, I'll admit that it's been quite a few years since I last studied the filtering spectrum plots of the Astronomik vs. the Lumicon UHC, so what I have to say is purely subjective. But I have an Astronomik UHC and two Lumicon O-III filters, and I consider them all to be quality equipment which suit me very well for visual use (I've never used them for imaging.). I've never felt like I should run out and replace my Astronomik UHC with a Lumicon brand filter or the Lumicon O-IIIs with Astronomik brand filters. Hope this helps.

#3 David Knisely

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Posted 11 December 2012 - 01:54 AM

The Lumicon UHC has a FWHM bandwidth of about 240 angstroms and is somewhat narrower than the Astronomik UHC (280 angstrom FWHM). The Lumicon UHC will reject skyglow just a little bit better than the Astronomik UHC, although the Astronomik will work pretty well too. My favorite narrow-band nebula filter has got to be the DGM Optics NPB filter, which is slightly narrower than even the Lumicon UHC is and also has a red secondary passband like the Astronomik does. Clear skies to you.

#4 Michael Rapp

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Posted 12 December 2012 - 01:19 PM

Thanks Scott, David. That's what I figured.

David - I ran across the comparison report between the Deep Sky, UHC, OIII, and H-Beta that you did some time ago. I was surprised at the degree of contrast enhancement the OIII gave on non-planetary nebula. For some reason I had gotten it in m my head that the OIII was primarily a PN filter.

#5 David Knisely

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Posted 12 December 2012 - 05:00 PM

Thanks Scott, David. That's what I figured.

David - I ran across the comparison report between the Deep Sky, UHC, OIII, and H-Beta that you did some time ago. I was surprised at the degree of contrast enhancement the OIII gave on non-planetary nebula. For some reason I had gotten it in m my head that the OIII was primarily a PN filter.


Well, the OIII can be quite good on many planetary nebulae, as often the OIII lines are the strongest for those objects. However, there are a few planetaries that have both OIII and H-Beta emission, and for those, a regular narrow-band nebula filter might provide a somewhat better view (examples: Campbell's Hydrogen Star and NGC 40). Diffuse emission nebulae also sometimes have OIII as their strongest components, so the OIII can be the best filter to have on some of them as well. The Veil is probably the best example of this OIII performance. On some objects, the narrow-band filters can show a larger area of nebulosity at a slightly higher brightness level, while the OIII will provide more contrast and sharpness to the nebula even if it does appear a little smaller in areal extent. There are also some specific details in certain diffuse emission nebulae that come out best in an OIII (or even an H-Beta) filter, so having more than one filter can be helpful. The narrower bandwidth of the OIII filter can also come into play when there is some significant skyglow, so those who observe under urban or suburban skies sometimes use the OIII filter instead of their narrow-band filters under those conditions. I like M27 in my narrow-band filter from my dark sky site, as it shows the most nebulosity, but in-town or under moon light, I will often switch to my OIII filter, as it rejects the skyglow a little more. This is one reason why I recommend people get both a good narrow-band nebula filter as well as a decent OIII filter, so you can choose which filter might work best on a given object or under varying skyglow conditions. Clear skies to you.






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