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More on O-III filters
by Chuck Hards 03 Jul '03

03 Jul '03

The coatings that make these narrow-band filters work are marvels of modern engineering, sometimes dozens of layers thick. They are interference coatings, so the thicknesses of these layers must be precisely controlled to 1/4 wavelength tolerances (sound familiar?). Lumicon states that their O-III filter has an 11nm bandpass, meaning that most of the energy passed by the filter consists of only wavelengths about 5.5nm either side of the center of the band. For O-III the lines we are interested in are at 496nm & 501nm, so 11nm encompasses both nicely if centered properly. A finicky feature of interference filters is that they are choosy about the angle of incidence of the light passing through them. This makes sense, as the angle of incidence increases, the light must travel through a longer path in the coating material, thus interfering at a longer wavelength when rebounding. There is a chance that Rich's filter is optimized for a fast Newtonian (at a higher angle of incidence)and Jims is happier at a longer focal ratio such as a "stock" SCT might work at (lower angle of incidence). Food for thought. Chuck __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com

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ATM
by justin 03 Jul '03

03 Jul '03

Hello, I have just discovered this group and am wondering if anyone will be teaching a telescope making class any time soon. I see from the archives that it has been taught before. Thanks. Justin Giovannoni jjon01(a)excite.com _______________________________________________ Join Excite! - http://www.excite.com The most personalized portal on the Web!

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RE: [Utah-astronomy] More on O-III filters
by Paul Witte 03 Jul '03

03 Jul '03

I have a Thousand Oaks OIII filter, but it's 1 1/4". If it's any indiciation though, I have been very pleased with it's performance. I also do recall looking at the Lagoon nebula using both my filter and yours last year with very similar results. --Paul ---------- From: Richard Tenney Sent: Thursday, July 03, 2003 8:20 AM To: Astronomy in Utah Subject: Re: [Utah-astronomy] More on O-III filters Chuck, The scope we tested this in has 100 inches of focal length at f/6.25; Jim's 10-inch I believe is f/7 or more which he also had no success with; I wouldn't call either of these scopes particularly fast. On the other hand, maybe we should try the TeleVue filter in a faster scope, say an f/4.5 and see what happens. But the bottom line was this -- the nebula was dramatically enhanced by the Lumicon filter, and only barely so (if at all) by the TeleVue, made even more obvious by my filter slide (both filters were loaded at the same time, and it was a simple matter of sliding each under the eyepiece (35mm Panoptic) without taking my eye away from the image. There was little if any difference between the TeleVue and the view sans filter. My Lumicon did come with transmission specs (in fact, I bought it from a dealer who had 3 of them sitting on the table, and was able to pick out the "best" of the 3). Jim, did your filter come with similar information? It would be interesting to repeat this test with other filters and/or filter manufacturers (anyone out there with a thousand oaks O-III in a 2-inch format?) and in different telescopes of varying focal lengths. -Rich --- Chuck Hards <chuckhards(a)yahoo.com> wrote: > The coatings that make these narrow-band filters > work > are marvels of modern engineering, sometimes dozens > of > layers thick. They are interference coatings, so > the > thicknesses of these layers must be precisely > controlled to 1/4 wavelength tolerances (sound > familiar?). Lumicon states that their O-III filter > has an 11nm bandpass, meaning that most of the > energy > passed by the filter consists of only wavelengths > about 5.5nm either side of the center of the band. > For O-III the lines we are interested in are at > 496nm > & 501nm, so 11nm encompasses both nicely if centered > properly. > > A finicky feature of interference filters is that > they > are choosy about the angle of incidence of the light > passing through them. This makes sense, as the > angle > of incidence increases, the light must travel > through > a longer path in the coating material, thus > interfering at a longer wavelength when rebounding. > > There is a chance that Rich's filter is optimized > for > a fast Newtonian (at a higher angle of incidence)and > Jims is happier at a longer focal ratio such as a > "stock" SCT might work at (lower angle of > incidence). > > Food for thought. > > Chuck __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy(a)mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy

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by Joe Bauman 03 Jul '03

03 Jul '03

Jim Stiley asked about my problems with my Meade LX200GPS 12" at Wolf Creek. I sent him this note, actually thinking it was going out to the whole list, but I guess it didn't. So here it is for the list, in hopes you all could respond to an idea I am mulling over about how to get my telescope on my Supewedge, at the end. Okay, true confessions, Jim. I'm turning pink over all my stupid goofs. I used my Superwedge and failed to realize I needed to put it into polar mode to work. Then when Don (I think it was) kindly pointed it out and I took half the night to figure out how to do that, it wasn't working properly because I didn't align it correctly. I misunderstood the instructions when it said not to use the handbox to align it on Polaris, so just aimed at it without using the handbox -- when I should have put it in the "home" position and then aimed at at Polaris by adjusting the mount, not the aim. I believed I compounded everything by getting the correction for magnetic declination on the wrong side of north, so instead of correcting, it made everything twice as far off! Finally, in the morning I discovered that the top bolt was not screwed in at all tight, leaving the base at an angle to the Superwedge, so the latitude had to be off just because of that if for no other reason. That's not to say mislaying my distance glasses and stumbling around in the dark a long time searching for them. These are difficulties that I won't have much trouble overcoming, I believe. What's much, much worse is that the telescope is too darn heavy for me to lift onto the Superwedge. I had no trouble lifting it from the back of the Jeep onto the tripod without the Superwedge, but the wedge adds a lot of height and puts the connection at a bad angle, instead of lying flat on the tripod. I had purchased some big cinderblocks from Buehner Block so I could stand on them and lift them onto the wedge, I thought, but that didn't work. It was still high and I was on the wrong side to lift it easily and I would have had trouble fitting the bolt into the slot with one hand while holding the telescope by the other. In this regard a competing wedge design is far superior as it has a small lip at the bottom, which is apparently where you can set the 'scope in place momentarily. I needed help to lift the telescope onto the wedge. Then I needed more help to put the two other bolts in place, because it was impossible to delicately slide something that heavy, and I needed help to lift it while I aimed it better. Also, I was afraid to try and lift it off. I thought if I loosened the bolt and held it with one hand, as I did with my Celestron 8", it would be too heavy to hold, even though the other hand would be gripping the handle. So I got it down by putting a blanket on the ground and heavy foam packing material on the blanket, then lowering the telescope onto the foam. Once on the ground, it was easy to unbolt. Here's what I am pondering, and I hope it's not a ridiculous idea. Maybe it's wrong and dangerous and I shouldn't do it. But I have been thinking about setting up the tripod and Superwedge, getting them aligned and level, then pounding a bunch of rebar and tent stakes into the ground, against the inside of two of the legs so they won't slide if I tip it. Then I would tip it over onto packing foam on the ground, where I would attach the telescope. Next I'd tip it back upright. If it was too heavy to do by hand, and I doubt it would be, I could use a tow-strap harness and pull it up using the Jeep. How does that sound to you all? Best wishes, Joe PS: Here's a story from today's paper with some quotes by our friends about the delights of star-gazing: http://deseretnews.com/dn/view/0,1249,510036458,00.html Joe Bauman science & military reporter Deseret News bau(a)desnews.com (801) 237-2169

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RE: [Utah-astronomy] Joe's woes
by Dale Hooper 02 Jul '03

02 Jul '03

Joe, You may also wish to consider the MAPUG or MAPUG digest lists. MAPUG (Meade Advanced Products User's Group) has provided a lot of info. that I have found very useful. There is also a great archive at mapug.com. Most of the archived posts are related to the LX-200 classics but much of the information is also applicable to the GPS. More and more posts lately are showing up related to the GPS. If I remember right, mapug is a majordomo list so you would send a message to mapug-request(a)shore.net with subscribe in the body of the message. Clear skies, Dale. > -----Original Message----- > From: Joe Bauman [mailto:bau@desnews.com] > Sent: Wednesday, July 02, 2003 7:54 AM > To: Astronomy in Utah > Subject: RE: [Utah-astronomy] Joe's woes > > > Hi Wayne, no, haven't joined -- sounds interesting. I'll look > into it. I > assume you start at Yahoo? Thanks, Joe > > >Joe, > >Have you been ready and joined the yahoo LX200GPS group? > Lots of good > >help at least for me. > >Wayne > > Joe Bauman > science & military reporter > Deseret News > bau(a)desnews.com > (801) 237-2169 > > > > _______________________________________________ > Utah-Astronomy mailing list > Utah-Astronomy(a)mailman.xmission.com > http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy >

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O-III filters: TeleVue vs. Lumicon
by Richard Tenney 02 Jul '03

02 Jul '03

FYI, Friday night (or more likely early Saturday) we had a filter showdown in my 16-inch on the Veil nebula; my 2-inch Lumicon O-III vs. Jim Gibson's new 2-inch TeleVue O-III (which by the way costs nearly $30 more). The difference was HUGE. Lumicon beat the pants off the TeleVue. In fact, the TeleVue was so bad you could hardly see a difference between the filter and no filter in terms of contrast with the nebula. Don't know if Jim just got really unlucky and happened upon a defective filter, but if this was any indication of quality, I'd highly recommend you stick with Lumicon (Jim's going to try for a refund in the meantime!). For those of you who haven't looked at the Veil through an O-III filter, it's rather dramatic -- one of my very favorite sights in the summer sky. You can spend a lot of time tracing the extensive loop in Cygnus... Rich __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com

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[Utah-astronomy] Fwd: [Planetary_Nebulae] Observing Planetary Nebulae with the 24 inch Clark
by UTAHDEB＠aol.com 01 Jul '03

01 Jul '03

For any of you that are thinking of going down to Lowell Observatory, I highly recommend it. Debbie

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Mars
by Barney B. 30 Jun '03

30 Jun '03

Is anyone getting any surface detail on Mars when using a C-8 scope? I've tried 130 power 162 power and 285 power with no success...well maybe I can see just the slightest hint of color change at 162 At 285 it's just an orange blob. This was at 4:30 A.M. last Saturday from Southeast SLC. Barney B.

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False Comet Cluster
by UTAHDEB＠aol.com 30 Jun '03

30 Jun '03

I observed the open cluster, NGC 6231, the "False Comet Cluster" as Stephen James O'Meara calls it this weekend both at Mountain Meadows and at the Virgin, Ut observing site. I observed NGC 6231 as well as Trumpler 24 to the north with my 4" refractor with the 55mm Plossl Sat night and with the 15" Obsession on Fri night.. O'Meara states "Open cluster NGC 6231 (Caldwell 76) forms the "head" of our pseudocomet and lies only 30' north of the 4th-magnitude double star Zeta Scorpii; the comet's "tail" is the large, elongated open cluster Trumpler 24 to the north. Although these objects have seperate catalogue identities, they belong to the same group of luminous stars, the Scorpius OB1 Association. I noticed the darker the skies, the more apparent this false comet cluster appears. At Meteor Crater last week, the false comet appearance was very obvious to the naked eye,, resembling a bent Eiffel Tower. O'Meara also says "Do not stop with NGC 6231. The entire region is worth exploring. Certainly there is nothing like it in the entire sky for small-telescope users. Just north and east of the cluster, out to about 3 degrees, are three open clusters (Trumpler 24, NGC 6242, and NGC 6268), a planetary nebula (IC 4637), a diffuse nebula (IC 4628), double stars, colored stars, Milky Way patches, and a swath of dark nebulosity (Barnard 48). It's a cornucopia of celestial riches."

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Re: 15x70mm binos for sale
by Chuck Hards 30 Jun '03

30 Jun '03

Thanks to all who responded. The binos have provisionally been sold, but as the first responder has not replied yet to my request to seal the deal, they just might go to the next person in line if he/she delays much longer. Offers will be extended strictly in order of receipt in my "IN" box. If you have already contacted me, stay tuned as you might get lucky. Hopefully we can get these to their new owner (whomever that may turn out to be) before the weekend. Chuck __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com

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