Frequently Asked Questions
Filters - General
Q:I am new to astronomy. What is the all-around best filter?
A:Unfortunately, there is no all-around best filter for everyone. The
optimum filter depends on your telescope / equipment, seeing conditions
and objects wanting to view. There are three basic categories of celestial
objects that can be enhanced with filters: lunar viewing, planetary viewing
and deep sky objects (faint objects like nebulae). There is no filter
that will do it all. However, information on finding what works best for
you can be found in Lumicon's Filter Specifications
and Uses page as well as the following FAQ's.
For observing the moon, the primary requirement is to reduce the light
intensity and enhance contrast for easy viewing. This can be done with
a Neutral Density or Polarizing filter.
For planetary observing, color filters bring out the most detail because
planets are naturally colorful. Different colors bring out different details
of the planet you are viewing. A description of each color filter and
what object it works best for can be found in Lumicon's Filter Specifications
and Uses page. Always remember that you want to use the darkest filter
your telescope will handle. Most small telescopes up to about 5" in aperture
use the light colors. The larger the telescope, the darker your filter
can be. Color filters can sometimes be used in conjunction with a Neutral
Density or Polarizing filter to aid in glare reduction. The more you use
your filters the more you appreciate them and their affect.
Q: What are the Scratch and Dig manufacturing specifications for Lumicon filters?
A: Lumicon filters meet MIL-PRF-13830B at the 60-40 rating or better. Lumicon filters meet MIL-0-13830 standard at the B level or better. This is actually much better than what is necessary since astronomy filters are used far from the focal plane. For more information, see Scratch and Dig Specifications.
Q:What are the specifications and uses of the various Lumicon filters?
A:See Filter Specifications and Uses.
Q:How do I clean my Lumicon filters?
Q:Why is the Deep Sky filter the only nebula filter recommended for photography?
A:Lumicon recommends the Deep Sky filter because it has the widest band-width
among Lumicon's nebula filters. The wide band-width of the Deep Sky allows
for shorter exposure times, which makes for easier astrophotography of
deep-sky objects. This is not a recommendation against narrower band-width
filters, such as the UHC or OIII, which can be used to produce higher-contrast
pictures. These narrower filters are more "challenging," however,
because they require longer exposure times. If you are new to astrophotography--a
difficult art--start with a Deep Sky filter. In terms of exposure time
required, from shortest to longest, Lumicon's nebula filters progress
as follows: Deep Sky<UHC<Comet<OIII<H-Beta.
Q: What is the transmission of the Lumicon Neutral Density Filter?
A: Lumicon's Neutral Density Filter is available in three transmissions:
13%, 25% and 50%. This means that they are blocking 87%, 75% and 50% of
the light across the visible spectrum.
Q: Does Lumicon carry both 1.25" and 48mm color filters?
Q:Does it help to double-stack filters?
A: Only for lunar and planetary observing, and even then, the only useful
combination is probably a neutral-density or polarizing filter to reduce
glare, in series with a color filter to enhance specific details.
Q: What are the thread sizes on Lumicon filters?
A:The 1.25" filters employ industry-standard 1.125" x 42 tpi threads
(except for Questar/Brandon, which use a thread pattern unique to Questar).
The 48mm filters employ industry-standard 48 x 0.75 mm threading, which
thread into 2" eyepieces. All larger filters use the given size with 0.75
mm pitch (e.g. a 72mm Minus Violet filter has 72 x 0.75 mm threads).
Q:Will Lumicon's Deep Sky filter work on small (e.g. 80mm) telescopes?
A:Yes, at low magnification, but do not expect nebulae to start popping
out all over the place. What the Lumicon Deep Sky filter will do is darken
the background of space, providing a more aesthetically pleasing view
of the sky.
Q: Do all Lumicon 48mm filters thread into a 2" eyepieces?
Q:Can the 48mm Lumicon Deep Sky Filter be mounted inside the Lumicon
Q:Can Lumicon Filters serve as dust seals on Schmidt-Cassegrain telescopes?
A: Yes. Visual Back Filters, as they are called, thread onto SCTs, accepting
visual back adapters.
Q:Does the Lumicon Multiple Filter Selector accept other brands of 1.25"
A: The Lumicon Multiple Filter Selector accepts nearly all brands of
1.25" filters. Filter cells up to 8mm thick (not including the threads)
Q:How does one distinguish Lumicon nebular filter types from each other?
A: For those who have inadvertently lost track of the identities of their
Lumicon filters, follow these guidelines:
The traditional Deep Sky Filter (Visual & Photographic) will make the
daytime sky or fluorescent lights appear a deeper blue than will the Ultra-High-Contrast
Filter. Its reflection from one side of the filter is silvery, and from
the other side, green-yellow.
The new Deep Sky II Filter (Visual Only) appears silvery on both sides.
Between the Oxygen III Filter and the Deep Sky Filter, the filter that
shows the Orion nebula best is the Deep Sky Filter.
The Oxygen III Filter will make the daytime sky or fluorescent lights
appear green. The reflection from both sides of the filter is green-yellow.
The Ultra High Contrast Filter will make the daytime sky or fluourscent
lights appear light blue. The reflection from both sides of the filter
The Hydrogen-Beta Filter will make the daytime sky appear red as seen
through it. The reflection from both sides of the filter is a very light
The Comet Band Filter will make the daytime sky or fluorescent lights
seen through it appear green. Tilting the filter sixty degrees will make
the daytime sky or fluorescent lights seen through it appear pink. The
reflecton from both sides of this filter is silvery if the angle of illumination
Q:What is the difference between 1.25" filters and Brandon 1.25" filters?
A:The 1.25" filters thread into standard 1.25" eyepieces, while Brandon
1.25" filters thread only into Brandon eyepieces. Brandon eyepieces are
used on the Questar telescope, which accepts only Brandons.
Q:Which Lumicon nebula filter is the best over-all?
A:The UHC filter is THE all-around nebular filter. It specializes in
showing nebulosity, even outperforming the Deep Sky Filter under suburban
skies. The UHC filter is a visual-use-only filter, but it can be used
in this capacity to great advantage from both suburban and dark-sky sites.
You would purchase the OIII and H-Beta filters separately only for specialized
high-contrast, and comparison viewing of certain nebulae.
Deep Sky Filter
Q:What is the Lumicon Deep Sky Filter all about?
A: The Deep Sky Filter is basically a general-purpose light pollution
filter that restores a dark sky background for viewing and photographing
deep sky objects from cities. It is the best light-pollution filter for
all astrophotography on the market today.
Visually, the Deep Sky Filter is the most useful filter under light-polluted
skies, from where it reveals star clusters, galaxies and nebulae.
Photographically, the Deep Sky Filter enables deep sky photographs to
be taken from cities, and it blocks some of the natural airglow at dark-sky
sites, thus improving deep-sky photographs taken from those locations.
Mercury light pollution occurs at 365, 405, 436, 546, 577, and 617nm.
High-pressure sodium streetlights emit at 570, 583, 600, and 617nm. The
Lumicon Deep Sky Filter blocks all of these.
Oxygen III Filter
Q:Will the Lumicon Oxygen III Filter work for photography?
A:Not very well. With enough aperture and patience, any filter will work
for photography. The Oxygen III filter's narrow band-pass is located near
the peak sensitivity of the human eye, and away from light-pollution lines,
so it works well visually. For most deep sky astrophotography, the broadband
Deep Sky Filter is your best bet.
Minus Violet Filter
Q:Does the Lumicon Minus Violet Filter perform well both visually and
Comet Band Filter
Q:What are the Lumicon Comet Band Filter's applications?
A:The Comet Band Filter is basically a nebula filter that happens to
show the ion tails of gaseous comets quite well. It can be used on other
objects. The filter has a narrow band-pass of 25nm that isolates the 501nm
Oxygen III and 514nm Cyanogen lines.
Night-Sky H-Alpha Filter
Q:Is the Lumicon Night-Sky H-Alpha Filter intended for solar viewing
or solar photography?
A:No. The Lumicon Night-Sky H-Alpha Filter was designed exclusively for
specialized dark sky astrophotography. It is simply a deep red filter
intended for nighttime use with Kodak Tech Pan black & white film.
Q:Does the Lumicon Night-Sky H-Alpha Filter perform well in CCD photography?
A:In pure reflectors, it will work well. In refractors, not so well,
because of its very broad band in the infrared. In Schmidt-Cassegrains,
its performance is intermediate.
Q:Does the Lumicon Night-Sky H-Alpha Filter come in more than one size?
A:Yes. The sizes are 48mm, 58mm, and 77mm. The 48mm fits all 2" eyepieces
and accessories. The 58mm and the 77mm are usually used with telephoto
Solar Prominence Filter
Q:What is the purpose of the required Energy Rejection Prefilter component
of the Lumicon Solar Prominence Filter system?
A:To protect the human eye from dangerous solar radiation.
Q:Why is an off-axis location required for the 58mm or 77mm Energy Rejection
A:Simply to avoid obstruction by the telescope's centrally located secondary
mirror. Unobstructed telescopes would not require an off-axis location
for the Prefilter.
Q:Is the Lumicon Solar Prominence Filter system safe to use on Schmidt-Is
the Lumicon Solar Prominence Filter system safe to use on Schmidt-Cassegrain
A:Yes. The Lumicon Solar Prominence Filter system was designed to function
normally on all commercial SCTs. Its 58mm or 77mm diameter Energy Rejection
Prefilter stops down the SCT's aperture, effectively producing a focal
ratio that lies within the optimum range to prevent overheating.
Q:Can the Lumicon Solar Prominence Filter be used on telescopes having
focal lengths shorter than 1200mm?
A: Only if a Barlow lens is used to produce an effective focal length
of at least 1200mm, and only if Lumicon's 58mm Energy Rejection Prefilter
is used. The Barlow lens must be located before the delicate narrow-bandpass
Thus, the components would occur in the following order:
1. Energy Rejection Prefilter
2. Telescope Objective
3. Barlow Lens
4. Narrow-Bandpass (1.5) Filter
Q: Can the 1.5 Angstrom bandpass component of the Lumicon Solar Prominence
Filter be used safely with other brand-name prefilters?
A: No, the reason being that the two filters of any brand-name Solar
Prominence Filter system comprise a matching set and must be used together
exclusively. Lumicon does not know the specifications of other brand-name
Solar prominence filter systems and therefore cannot recommend the indiscriminate
use of its 1.5 Angstrom bandpass filter component with other brand-name
energy rejection prefilters.
Q: Can I look at the sun directly by holding the prefilter in-front of
the 1.5 Angstrom filter?
A: No! The two filters, in combination, require a substantial image magnification
in order to reduce the light intensity to a safe level.
Q: What is the lifetime of the 1.5 Angstrom bandpass component of Lumicon's
Solar Prominence Filter system?
A:15 - 20 years. The lifetime is shortest near the ocean or in regions
of high humidity.
Q: Is the Energy Rejection Prefilter included with the purchase of a
Lumicon Solar Prominence Filter System?
A:Yes. The customer specifies his telescope type when ordering, and Lumicon
then selects the appropriate Energy Rejection Prefilter.