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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 specifications and uses of the various Lumicon
filters? |
| A: |
See Filter Specifications and Uses.
|
| Q: |
How do I clean my Lumicon filters? |
| A: |
See Cleaning. |
| 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 48 mm color filters? |
| A: |
Yes. |
| 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 48 mm 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 72 mm Minus Violet filter has 72 x 0.75 mm threads). |
| Q: |
Will Lumicon's Deep Sky filter work on small (e.g. 80 mm)
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 2-inch eyepieces?
|
| A: |
Yes. |
| Q: |
Can the 48mm Lumicon Deep Sky Filter be mounted inside the
Lumicon Easy Guider? |
| A: |
Yes. |
| 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" filters? |
| A: |
The Lumicon Multiple Filter Selector accepts nearly all
brands of 1.25" filters. Filter cells up to 8 mm thick (not
including the threads) are accommodated. |
| 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 is silvery.
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 blue.
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 is high. |
| 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. |
UHC Filter
| 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 photographically? |
| A: |
Yes. |
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 lenses. |
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 Prefilter? |
| 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 telescopes? |
| 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 (1.5 Å) filter.
Thus, the components would occur in the following order:
1. Energy Rejection Prefilter
2. Telescope Objective
3. Barlow Lens
4. Narrow-Bandpass (1.5 Å) Filter
5. Eyepiece |
| 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. |
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