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Which Neutral Density Filter?

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#1 Simon Green

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Posted 05 March 2018 - 12:09 PM

I have a 130mm apo refractor, and I want a Baader neutral density filter for use with it for (some) lunar observing.  The question is, which Baader neutral density filter? 

 

I'm thinking either the 0.6 neutral density filter (25% light transmission) or the 0.9 neutral density filter (12.5% light transmission).  Comments?  Suggestions?

 

I know that I can get by without a neutral density filter, but I have already made the decision to get one to see what it can do for me.  The question is, which one?

 

From my readings, it appears that most "lunar filters" offered for sale (by Vixen, Orion, etc.) are 12.5% light transmission, so maybe I should choose that, but, on paper, 12.5% seems like so little light!

 

Thank you.

 

Simon



#2 GDAstrola

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Posted 05 March 2018 - 12:25 PM

I have done well with the Orion 1-1/4" variable polarizing filter to adjust transmission to compensate for lunar brightness changes and differing apertures.

 

A CN thread to look at also,   https://www.cloudyni...arising-filter/

 

 


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#3 HarryRik9

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Posted 05 March 2018 - 01:17 PM

The issue is that as the moon phase increases the amount of light increases rather significantly. That is why the adjustable type is a good idea. 


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#4 mrowlands

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Posted 05 March 2018 - 01:29 PM

I have the 50, 25, and 13 for my various size scopes.  Before cataract surgery, it helped the views when cutting the brightness way down.  Now I still find it more comfortable to knock it down a little.  So depending on your sensitivity, I'd say the 50 or the 25 for your 5 inch scope.  Or the variable polarized filter.

 

Mike R.



#5 wcw

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Posted 05 March 2018 - 01:35 PM

I used the Orion variable polarizing filter for years. Out of curiosity I tried the Lumicon 13% neutral density filter and wow the image is noticeably sharper. I liked it so much I spent the money to buy the 25% and the 50% versions. I use them all but the 13% is the one I use when the moon is near full.

 

My scope is a 140mm refractor.

 

-Bill


Edited by wcw, 05 March 2018 - 01:35 PM.


#6 Alan French

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Posted 05 March 2018 - 07:32 PM

Observing with 8 to 10-inch telescopes, I don't find filters necessary. It's just a matter of spending enough time to get used to your telescope's brightness level.

 

I note that Alika Herring, whose fine lunar drawing graced the pages of Sky & Telescope long ago, makes no mention of filters, nor does Harold Hill, author of "A Portfolio of Lunar Drawings." Hill does make some interesting comments under "Some thoughts on the art of vision" on page xx of his book.

 

Clear skies, Alan



#7 kcb

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Posted 06 March 2018 - 12:14 AM

because I am actually studying the moon with my 6'' f8 apochromat and c14 sct, I find I can get away without filters with the 6'' because I use highest possible magnification along the terminator , however, the vixen moon filter gets more use as it has surprised me over the N.D filters and polarizers as being quite good optically , I have had it for many years , certainly use it on the celestron ( orange c14 ) and the 6'' refractor at lower powers ,maybe they were made better back then but I see they still sell them today



#8 GDAstrola

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Posted 07 March 2018 - 01:11 AM

This Lumicon 2" ND13 filter appeared recently on CN

 

.https://www.cloudyni...nd13-2”-filter/

 

Good luck.



#9 azure1961p

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Posted 07 March 2018 - 07:58 PM

I know it sounds like too little light but believe it or not its still too bright.

Ill even add a wratten 21 on it to further surpress glare with my 8 inch at 200x.

 

Pete


Edited by azure1961p, 07 March 2018 - 08:04 PM.

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#10 M57Guy

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Posted 10 March 2018 - 12:36 PM

IMO, its a matter of preference and just about any variation can be beneficial under certain situations.
I prefer the variable variety when Luna is > 50% illuminated.
 

Ill even add a wratten 21 on it to further surpress glare with my 8 inch at 200x.

Also, I'll add another vote for the #21 filter as an alternative to a ND for good contrast on craters.



#11 Exnihilo

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Posted 26 March 2018 - 11:16 AM

I have done well with the Orion 1-1/4" variable polarizing filter to adjust transmission to compensate for lunar brightness changes and differing apertures.

 

A CN thread to look at also,   https://www.cloudyni...arising-filter/

I use the Orion variable filter as well.  Really happy with it.  I also have the 2-inch one.



#12 AxelB

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Posted 26 March 2018 - 04:25 PM

On an 8" sct, I found the 13% too dark. I prefer the 25%. When the moon only shows a tiny crescent, the 50% is enough.

If you get only one, buy a 25%.

Edited by AxelB, 26 March 2018 - 04:26 PM.

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