University Lowbrow Astronomers

Fooling Around With Filters.

by Gary Perrine
Printed in Reflections: October, 2002.

Every month I receive this e-mail from Mark Deprest and it says, Pleeeese!!!  Send me some articles for the newsletter.  Anything will do.  Come on I’m really hurting this time.  Something about your new scope.  Maybe something about an eyepiece.  A picture of your dog or cat wearing a Captain Nemo hat and goggles.  I’ll put it in the newsletter.  I swear.

Well I can’t take it anymore.  I’ve been a member of this wonderful organization for around three years now and have never written an article on anything.  So I’m feeling guilty about it.  So I say to myself, Gary, get a little ambitious.  Go upstairs to the computer, get out your one and only typing finger, and do something to cheer Mark up a little.  He sounds like he needs it.  And he deserves it.  He does a great job on our newsletter every month.  So here goes.  I thought I’d submit a short article about using color filters for visual planetary viewing.  The reason I picked this topic is because I don’t really remember reading very much about them in our newsletter since I’ve been receiving it.  It doesn’t seem to me like many people use them much or maybe they just don’t talk about using them very often.  I use them quite a bit because I like planetary viewing.

I remember when I first got into this hobby, when Hale-Bop came through and I bought my first telescope, a Celestron 80mm WA, not the best setup for looking at planets.  I’d read how color filters could enhance the detail on planets that you couldn’t see very well when looking through an unfiltered eyepiece.  OK, I thought, here’s the magic fix for this little 3 in. scope that I can barley see some faint lines in Jupiter and Saturn with.  And they’re fairly cheap too compared to buying a bigger scope, only about 40 bucks for a starter set of four.  Can’t wait till the mailman drops these babies off.  I’ve been wanting to see if that ice on Europa and those volcanoes on Ganymede look the same as they do in Sky and Telescope.

Well Orion did their job as expected and promptly shipped my filters.  The post office did their job and delivered them to me via a dapperly clad official US Postal Employee.  My first night under the stars with them I did my job of threading the dark blue one into an eyepiece without cross threading it TOO MUCH.

Hey, what’s the deal?  Instead of Jupiter looking like a round thing with faint fuzzy lines in it, it had now taken on the appearance of a round blue thing with faint fuzzy lines in it.  Well, at least it’s still round.  Think I’ll just find a cozy out of the way place in the accessory case for these for a while.

It wasn’t until I got my dose of aperture fever and bought a larger scope and tried the filters through it that I realized, these little things do kind of work like they’re supposed to.  You just need to use optics that you can see the detail on the planets reasonably well to begin with.  The way these little colorful do-hickeys work is they help reduce irradiation, which is the distortion between the boundaries of the lighter areas and darker areas of the Moon’s or a planets surface caused by turbulence in the atmosphere that we are looking through.  They also help to increase contrast by blocking out some of one color while enhancing another color of two adjoining areas of the Moon or planets such as the bands of Jupiter, or the Cassini division in Saturn’s rings.

Since my original purchase of the starter set of filters which consisted of a # 25 red, a # 58 green, a #15 yellow, and a # 80A blue, all darker shaded filters, I’ve bought two more, a # 8 light yellow, and a # 82A light blue.  I’ve been pretty happy with the results I’ve had with the #15 deep yellow filter while observing Saturn and Jupiter.  This filter really seems to help me be able to see more detail on both these planets.  The #8 light yellow is ok too but doesn’t seem to help out as much as the darker one while only using yellow as a filter.  The # 80A dark blue has given some good results too but I still prefer the Yellow.

While in Pennsylvania I bought the #82A light blue one.  I think I like this one the best so far.  It seemed to work great by itself on Jupiter.  Then I thought to myself, I wonder what will happen if I couple this together with the light yellow one?  It seemed to enhance contrast and detail better than any of the other filters that I have.  I’ll probably use this combination quite a bit.

I don’t really get too much use out of the red and green filters.  The red just seems too weird when I look at anything through it.  The dark green one is supposed to be good to use on Mars, but I’ve never had a whole lot of luck observing that planet no matter what I’m looking at it with.  I thought I saw the polar caps once but it may have just been a dirty eyepiece lens.  I’m just not a real Mars kind of guy I guess.  Although I am tempted to put it in while looking at the Moon sometime and telling some youngster, see it really is made of green cheese, now always believe everything your parents tell you.

I guess the bottom line on the subject of color filters for me is, if you can buy a couple of these things at 12 to 15 bucks a pop, and they can help to pull out detail a little, or quite a bit as I’ve found to be the case with a couple of mine, they’re well worth the considerably small cost compared to some of the other accessories we’re willing to shell out our hard earned bucks for.

Well, that’s the end of my first article.  Actually that was kind of fun.  Think I’ll try another one some time.  Oh, two words of caution I should mention before ending this.

#1- In case someone new to this astronomy hobby is reading this, never use a color filter to look at the Sun with.  Use only an approved solar filter.

#2- Don’t get any silly ideas about buying two of the red filters and taping them onto your eyes and using a nice bright white light to read your sky maps with.  It’ll just tick everybody off.

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