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nightowl
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will variable polarizing filter reduce some color
      #5938525 - 06/24/13 06:37 PM

Hello,

I'll be heading out to the desert this Thursday with my 6" f/5 acrhomatic refractor. Normally I go out at this time of the year to get to globular clusters in Sagittarius and beyond. Thus, my viewing of deep sky is usually done with 15mm to 20mm eyepieces.

However, this Thursday, the waning moon will rise at about 11:15 pm. I will employ my scope to view some craters.Given my scope has a short focal length and induces color, will a variable polarizing filter used on it reduce the achromatic color when viewing a bright moon? If not, will a #56 green filter be better? Thanks.

Jack


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brianb11213
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Re: will variable polarizing filter reduce some color new [Re: nightowl]
      #5938547 - 06/24/13 06:56 PM

Quote:

will a variable polarizing filter used on it reduce the achromatic color when viewing a bright moon?



No.

Quote:

If not, will a #56 green filter be better?



Yes, but a pale yellow should be sufficient to remove the false colour in a fast achromatic. If you want to try a blue / green then a OIII or hydrogen beta nebula filter will work well on the moon, completely removing chromatic aberration however bad the scope is and providing sufficient density to make the moon comfortable to view.


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nightowl
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Re: will variable polarizing filter reduce some color new [Re: brianb11213]
      #5938637 - 06/24/13 08:02 PM

Hi Brian,

Your information says it all. Thanks a lot and clear skies!

Jack


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azure1961p
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Re: will variable polarizing filter reduce some color new [Re: nightowl]
      #5938798 - 06/24/13 10:05 PM

Yes it will *remove* color but only because its such a powerful filter - everything gets darker including the CA.

Your best bet by far without hesitation is BAADERS Moon and Skyglow Filter/Fringe Killer combo all in one filter. The Fringe Killer by its is an awesome filter but in conjunction with the MSG filter it renders a less yellow more natural color balance. The yellow isn't bad at all however. At anyrate I frequently stack my MSG with the FK and its wonderfully color free. You may see a sllliiggghhhhttt purple fringe hint - but that's it.

I couldn't recommend a better more effective filter for your scope. Wether or not you want the MSG combo is your choice. I chose seperate filters and simply stack when needed.

Pete


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brianb11213
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Re: will variable polarizing filter reduce some color new [Re: azure1961p]
      #5939152 - 06/25/13 04:22 AM

Quote:

Yes it {polarising filter} will *remove* color but only because its such a powerful filter - everything gets darker including the CA.



All the light is reduced by a similar amount. There is a second order effect where reducing the light level makes the eye notice the violet halo a bit less but this is counterbalanced by the transmission of crossed polarising filters tending to increase in the blue/violet. Another second order effect. The notion that a variable polarising filter behaves like a neutral density filter is close enough to reality.

Quote:

The Fringe Killer by its is an awesome filter but in conjunction with the MSG filter it renders a less yellow more natural color balance.



Yes, if I was using a short focus achromat I wouldn't want to be without the fringe killer or something with a very similar performance. I don't like the MSG though, it has insufficient transmission for deep sky objects yet isn't dense enough to be comfortable on the moon.

Funnily enough the filter I keep turning to for visual use on the moon is the Baader Solar Continuum filter ... a near-monochromatic green filter of a similar type to the "nebula filters" but with a passband centred on a region of the spectrum without significant emission / absorbtion features.


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azure1961p
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Re: will variable polarizing filter reduce some color new [Re: brianb11213]
      #5939257 - 06/25/13 08:01 AM

It's funny - I love the moon and Skyglow filter but I'd never consider it a moon filter in any way, shape or form. Why they add the moon in the title is beyond me unless they are referring to the Skyglow created by the moon illuminating the night sky? Yes it's too tame to supress any moon glare directly.

Pete


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nightowl
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Re: will variable polarizing filter reduce some color new [Re: azure1961p]
      #5944964 - 06/28/13 03:04 PM

Thanks for chiming in everyone with good information. Well, just got back from an overnight stay at near the legendary White Mountain in California. About 20 minutes into the viewing session, my 12 volt power supply died and that killed the GOTO viewing session. Then I tried manually moving my scope on the EQ mount but it was overall a clumsy experience to star hop. I drove 5 hours from Los Angeles to a site to view for only about 40 minutes. A headache developed soon after from the high altitude (9K feet plus). Then I went to bed under the stars. It was a shame really because the seeing, transparency and lack of wind made for ideal conditions! Didn't even get a chance to welcome the rising moon with the scope. Better luck next time, sigh. One can't get mad at the universe. Clear skies. Jack.

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