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Frequently Asked Questions


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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?

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 48mm 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 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?

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 8mm 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) 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) 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.