Program- Filter Roundup Don Surles– Amateur astronomers use filters
to improve image contrast. There are versions for solar, lunar,
planetary, and nebula viewing.
Here are some comments about several types of filters.
Solar viewing – normally solar filters are aluminized glass
or aluminized mylar film, light reducing glass (welders lens), or a solar
film such as Baader Solar Film. The filters reduce incoming
light to a small fraction of the amount available and blocks ultraviolet
light so that it is safe to view our star. My favorite is Baader
Solar Film. A polarizing filter in conjunction with a solar filter
improves the surface detail contrast.
Lunar viewing – here we can use neutral density, polarizing,
or colored filters. Neutral density filters reduce the incoming
light uniformly across the entire spectrum, ie, in camera terms they reduce
the aperture. Polarizing filters improves the contrast and enhance
surface relief. Colored filters also reduce light but change the
color of the image.
Light pollution reduction filters are designed to block light
of certain wavelengths – normally the wavelengths associated with manmade
urban street and advertising lighting. The telescopic image appears
against a darker background; thus contrast is enhanced. These filters
work very well in light polluted areas.
Minus violet filters are used to reduce the chromatic aberration
associated with short focal length refractors of the doublet (fraunhoffer)
design. I have tried these on 6 inch f-8 refractors and found them
to work very well.
My favorite filters are the so-called nebula filters that are
used for improving the viewing of various nebulae. I do not try to
remember the wave length of light each affects…I enjoy trying different
filters on my favorite objects such as the Veil, Dumbell, Swan, Ring, etc.
Examples of these filters are the Lumicon UHC and OIII, and Orion’s Skyglow
and Ultrablock. I cannot
detect a difference in Lumicon and Orion versions.
The Horsehead filter? I don’t own the so-called
Horsehead filter but it is on my list.
Colored filters…varying shades of Red, Green, Blue, and Yellow,
improve the surface details to be seen on our sister planets (why don’t
we have some “brother” planets?). Try them all – the results
can be different from night to night for Mars, Jupiter, Saturn and Venus.
There are other filters that allow us to see solar prominences (Daystar,
Coronado) and our own Prom Scope with a 1 nanometer filter centered on
656.3 nm.
So, if you want to learn which filter suits your scope, eyepieces,
and viewing habits, find someone with a case full of filters and try them.
And tell Santa what your needs are…filters make excellent stocking stuffers.
You can also read the side panels of Orion Telescopes’ catalogues – there
is a wealth of information in the Orion catalogue.
Don…
From the President’s Desk....
April 16, 2003 Are your taxes paid? I hope so.
It’s now Springtime and that means warm weather, fresh flowers, sittin’
on the back porch, and hopefully, some star gazin’. All that
1040 stuff is in the past; the war is winding down…time to relax and enjoy
life.
Mars is coming! We are sending two Rovers to explore the planet and
the European Space Agency is sending British-built Beagle 2 aboard the
Mars Express via a Russian Soyuz-Fregat launcher. Our Rovers will
tool around the planet looking for clues to what happened to Mars over
the eons of time. Each Rover weighs approximately 400 pounds and
is not tethered to a
base station as was Pathfinder – they are self contained and can move
about freely. The Beagle 2 (named after Charles Darwin’s ship that
took him to the Galapagos) will be dropped to the surface and will dig
as deep as five feet down for samples that could contain water. It
will also look for clues about the possibility of past life on Mars by
measuring carbon isotope ratios.
Mars Express will orbit the planet and act as a communications tower
for Beagle 2 plus it will continue to map and analyze Mars. The ultimate
goal of all the missions is to find water in some form. Stay tuned
for additional details as the missions unfold. These missions should
be much more productive than 1997’s very successful Pathfinder – remember
how exciting it was to actually see the surface of Mars and in 3-D?
Let’s hope these new missions are successful…our (USA, Soviet Union, and
Russia) track record for missions to Mars is less than perfect. But
practice does make perfect.
MARS IS COMING! Amateur astronomers should be preparing for the arrival. We need to get the best scopes possible, the best eyepieces, some colored filters, a solid mount, and dedicate some of our time to watch the approach of our neighbor planet. Be prepared to spend some time (more than just a glance) at the eyepiece – you will be surprised at how Mars’ surface changes over just a short period of time. You will also be surprised at how the image increases in size over a period of a few days.
I finally took my Meade 10” F-4 Schmidt-Newtonian and it’s Orion Atlas
mount out for first light last Saturday night. The moon was nearly
full but the sky was clear, the temps were just right and the Blackbird
Forest mosquito did not attend. Even though I played basketball with
the scope a couple of weeks ago (I dribbled it on the driveway) it performed
very well.
The Atlas mount is sturdy and carries the scope without excessive wiggles
and vibration.
Overall, Scope and Mount both earned the Surles Stamp of Approval.
Next test is to put a camera on the scope
and check out the drives’ errors.
Delmarva Star Gaze IX…it’s almost here. We have ordered
clear and dark nights, about 55 degrees at night and 80 in the afternoon.
The trees will be wearing their new Spring outfits for your visual enjoyment.
There will be music by Mother Natures Critters of the Forest ensemble.
And amateur astronomers will have the best time ever. So get your
gear and make the trip to
Tuckahoe. You will enjoy the getaway. Coming events: We will
begin a project to mplete a large mirror for a Club scope this summer.
So if you would like to learn the how-to’s of finishing a large mirror
please contact Lyle, Keith or me. This project will be a lot of fun
and it will be a great learning experience.
What are your astronomical needs? Please give this some thought
and pass along your desires – it is possible that your Star Gazers can
help. Our organization has a lot of talent, expertise (a lot of “been
there and done thats”…), and some pretty sophisticated equipment of just
about every sort. You are not alone…your fellow amateur astronomers
can help and we do like to help. Just ask…
Til next time, Don…
New Newsletter Format- The first physical change in the
newsletter will be trying other type faces. In this issue ,we have
switched to a typeface which is much easier to read in the smaller
font sizes.
In actual content, we are still feeling our way with emphasis
on the things that we do best; amateur and observational astronomy.
We intend to involve as many people as feasable Much will be abstracted
from postings on the DMSG Yahoo pages. This alone means that more people
will participate in the content of the newsletters. There are certain
things we can do better than the regular Astro Magazines, like the personal
observations sessions.
Also, in reviewing equipment, as hardcore amateurs, we can let you
know when the emperor’s wearing no clothes.
A case in point was Don’s recent review of LXD55.
This practical approach doesn’t mean that we will shy away from highly
technical subjects like cosmology; very often, one can present these subjects
in a fresh manner that will spark the interest of everyone. A PBS
program recently took a subject like nuclear synthesis in stars and
whipped it into a lively show by emphasizing the theme that everything
and everyone in the universe, with no exceptions, was made in a star.
Nifty stuff....
There are also areas where amateurs can contribute to the body
of astronomy itself. Our former member, Paul Gray, from Canada co-discovered
a supernova and when you think about it, most of the comets are discovered
by amateurs. There are certain areas of astronomy that actually
depend on amateur input. Cataloging Double stars offer something
for everyone and for every size scope, from enjoying the actual beauty,
to measuring the separation and even orbital motion.
Observing and measuring magnitudes and periods of variable stars,
depends almost entirely on amateurs. It is done through the American Association
of Variable Star Observers (AAVSO). The Amateur’s observations are
entered into the AAVSO international data base.
International Occultation Timing Association (IOTA) is another group
that encourages amateurs with CCD Camcorders to record asteroid occultations.
These data submitted from a variety of sites allow astronomers to determine
the actual shape of the asteroid.
Another opportunity is astrophotography where amateur’s images rival
those of the pros. In April of 2000, our stargazers turned in images
of Aurora Borealis equaling anything in the astromags.
Doug Miller’s images have appeared a number of times in the astronomy
picture of the day. So get over to the Yahoo pages and introduce
yourself. Tell us about yourself and the specific areas in astronomy
which interest you. Together we can write the newsletter.
Frank Sheldon