I've had the opportunity to test 3 non-color filters.  They have been the Celestron LPR filter and the Lumicon 0-III filter and Lumicon UHC filter.  Read about my experiences below.

Celestron LPR Filter

June 5, 2003

Moon was about 35% and about 30 degrees up in the west when I went out. 

I’m probably in a great location to evaluate a Light Pollution Filter :  Clear dark skies except to the south and southeast.  Columbia City (population about 4000) is south 2 miles and Fort Wayne (population about 220,000) is southeast about 20 miles.  So here are the results and associated comments:

Looking south and southeast, the filter does a great job of taking the murky gray sky and making it black.  But, stars do not stand out much better because they seem to be equally dimmed through the filter.  I looked at globular clusters M4 and M80, both near Antares in Scorpio.  Both were difficult to discern without and with the filter– M4 tougher than M80.  Both were actually better without the filter.  Next, I went to M104 – The Sombrero Galaxy in Corvus.  Basically, I had the same disappointing results.   

I then wanted to test in a darker section of sky.  I went to M51 which was nearly at zenith.  Since the sky was already dark, the filter did little as far as background.  What it did do was almost kill M51.  The galaxy was much better without the filter.  The same applied to globulars M13, M3, and M92. 

At this point, you would think it is time to forget about the filter.  Then, since it was a couple of hours later, M57 (Ring Nebula) and M27 (Dumbbell Nebula) were high in the sky.  This is not a badly light polluted part of the sky for me.  Both were visable without the filter but ‘unimpressive.’  With the filter, both were awesome!  They really stood out well against the dark sky surrounding them.  This was a “Ahaa! Moment.”  It appears that emission nebulas and planetary nebulas will be nicely enhanced with the LPR filter and galaxies and clusters will see little benefit and may actually suffer with the filter.  Now, I can’t wait till fall and winter to revisit M42 and M1! 

I did notice that the surface of the filter appears highly reflective.  This seems to produce a reflection off of your eyeball in the eyepiece if lights from the moon or car headlights hit you.  Not a big deal, but interesting.

So, the filter does work – in very specific situations.  And it actually hinders performance in other situations.  Now I need to test some other nebular filters and an O-III filter.  I’m guessing there is no single ‘magic pill’ filter to use.  It will all depend on what you want to look at.

Lumicon UHC Filter

I bought this filter from Anacortes along with the Lumicon O-III.  My gut feeling was that these would be a cut above some of the other filters advertised and I was willing to spend a little more.  Price was $99 for the 1 1/4" filters. 

To cut to the bottom line, this is by far the best nebular filter that I have tried.  The enhancement of nebulas was better than  with the Celestron LPR plus it didn't dim the surrounding stars any worse.  This adds up to better contrast. 

I have observed a number of objects on several nights, both from my slightly light polluted home and from my much less light polluted site south of Columbia City.  The most dramatic example has proved to be M97 - The Owl Nebula.  Though it appears to be in a fairly dark area of sky, I had not been able to see it through the Nexstar 8i.  The Lumicon UHC changed that.  The filter does not make this an awe-inspiring sight - but it does make the difference between seeing and not seeing.

Turning to the area of Sagittarius, The filter presented much improved view of the Swan/Omega nebula M17.  This was the first time that I could clearly make out the Trifid Nebula M20.  The area around M18 was awesome through a 40mm eyepiece with the UHC filter.

After being very impressed with the southern sky, I went to the Ring Nebula M57 and the Dumbbell M27.  Both objects were tremendous with the filter.  They are not bad without a filter, either.

As with the Celestron LPR filter, this filter surface is highly reflective and an effort needs to be made to keep local light from hitting your eyeball and reflecting back at you.  You do NOT want this filter inline when viewing clusters and galaxies.

All-in-all, this is a great filter.  I tried to wear the threads out putting it in, and taking it out.  Very nice...

Lumicon O-III Filter

This filter was purchased from Anacortes.  The 1 1/4" version was $99.  I had 3 sessions out under dark skies with this filter.  I had heard great comments about using O-III filters when viewing emission nebula.  One comment in the Nexstar User Group was something like "you haven't lived till you have scanned the Veil nebula from a dark site with an O-III filter in a 20 inch Dob."

Well, I tried.  Unless I was doing something wrong or there was something wrong with the filter (I doubt it - I talked to Lumicon), I found the filter of little help to me.  That doesn't mean that O-III filters don't do all of the great things that you hear about.  My theory is this:  My skies are a little too light polluted and/or the 8" Nexstar SCT just doesn't gather enough light to see the faint objects that it works best on.

Anacortes agreed to take the filter back.  I will find a better way to spend the $99.  Let me know about your experience with O-III filters.

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