Last updated: 14 February 2006
Subject:	Nebula Filter - Lumicon Deep-Sky versus UHC
Sent:	Friday, February 10, 2006 11:53:37
From:	Ken Toliver (
The following is a conversation that I had with Lumicon Technical
Support regarding proper selection of a nebula filter for the ETX125. I
hope it will be helpful for others looking to pick up one of these
filters. My primary concern was whether the UHC would pass too little
light to be useful in a scope with only a 5" aperture under moderately
light polluted skies. Based on their response it does appear that the
Deep Sky model is preferable under these conditions. I will post a
review after I receive and field test the Deep-Sky filter.

Ken Toliver
Scottsdale, AZ
Dear Mr. Toliver,

You're welcome.

The UHC can be used on the ETX 125 for viewing the brighter nebulae.  
The rule-of-thumb is, the bigger the telescope, the narrower a filter
can be used, to good effect.  It is not black-and-white, however.  The
differences between the filters are in shades of gray.
And at some point, personal preference enters the equation.

Peter Wilson
At 10:15 AM 2/10/2006, you wrote:

Thank you for the recommendation. I understand that the filter is
primarily for viewing nebula which is my desire. I will purchase the
Deep Sky model as you suggested.

However, for my own edification can you tell me when, if ever, the UHC
would be desirable for my telescope? Is the telescope itself part of the
limiting factor?

Ken Toliver
From: Peter Wilson (
Sent: Friday, February 10, 2006 10:12 AM
Subject: Lumicon Deep Sky versus UHC

Dear Mr. Toliver,

Thank you for your interest in Lumicon.

I recommend that every back-yard astronomer have at least one nebula
filter, and one lunar/planetary filter.  For the Meade ETX 125EC, I
would recommend the Deep Sky for viewing nebula.

Notice that I say nothing about light pollution.  Nebula filters work,
in part, by blocking light-pollution, but they do not magically
transport you to a dark-sky site.  If your primary observing interest is
in star-clusters and galaxies, nebula filters will not improve the view,
because they block starlight as well as light-pollution.  I am not
trying to discourage you from buying a nebula filter--as I said, every
observer should have at least one--I just want to make sure you
understand that nebula filters are for viewing nebula, not stars and


Peter Wilson
Tech Support
Lumicon International
From: "Ken Toliver"
Subject: Lumicon Deep Sky versus UHC
Date: Thu, 9 Feb 2006 16:37:18 -0700

I am ready to purchase a Lumicon filter for my telescope but would
appreciate some guidance on the selection process. As a casual observer,
I do not have a complete grasp on every aspect of focal ratio versus
focal length versus exit pupil, etc., to help me make an informed
decision. My intention is to get better views of DSOs.

My telescope is the Meade ETX 125EC which is a Maksutov-Cassegrain;
clear aperture is 5, focal length and ratio is 1900mm f/15. I live about
30 miles north of Phoenix and my views to the north are pretty dark
(mild light pollution), however my views to the south are more
intermediate to heavy light pollution. I like to utilize my scope
primarily from my back-yard; however I also travel to some very dark sky
locations now and then.

From my review of your site information, it appears that the focal
length and ratio of my telescope may actually be the limiting factor
pushing me towards the broadband Lumicon Deep-Sky instead of the
narrow-band UHC. What is your recommendation based on my particular
piece of equipment?

Ken Toliver

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