- Utah-Astronomy - mailman.xmission.com

TeleVue 55 Plossl for sale
by astrodeb＠charter.net 14 Feb '05

14 Feb '05

Time to clean out the closet so I thought I'd post it here before putting it on AstroMart. This eyepiece gives wonderful wide-field views. I saw the North American Nebula and the California Nebula with it last year. Debbie

2 1

Re: Question on focus
by Canopus56 12 Feb '05

12 Feb '05

Brent Wilson wrote: > I have found that laser collimation is only a rough > alignment procedure. The final touch needs to be made > by eye, . . . As always - a final tweak to one's personal preference is done with eye. > . . . preferably using stars in the center of the field of view. A carefully marked mirror center and a peephole alignment . . . Nice trick with the star. I'll have to give it a try. I guess it's a matter of skill and experience. No matter what I do, laser collimation seems to get it that last bit that I can't do by eyeballing it. - Canopus56 __________________________________ Do you Yahoo!? Read only the mail you want - Yahoo! Mail SpamGuard. http://promotions.yahoo.com/new_mail

1 0

Re: Question on focus
by Canopus56 12 Feb '05

12 Feb '05

Looks like that table on Sinnott's diffraction limited FOV width didn't go through listserv properly, so here it is in html: http://members.csolutions.net/fisherka/astronote/astromath/DiffractionLimit… - Canopus56 __________________________________ Do you Yahoo!? Meet the all-new My Yahoo! - Try it today! http://my.yahoo.com

1 0

Re: Question on focus
by Canopus56 11 Feb '05

11 Feb '05

Patrick wrote, > If anyone is interested, I have S&T going back to > the first issue in my library. If y'all can come up > with the issue the article is in I'd be happy to > bring it to the next SLAS meeting The article I mentioned regarding the size of a scope's sweet spot was: Sinnott, Roger W. May 1991. Focus and Collimination: How Critical? Sky&Telescope pp528-531. Sinnott's equation for the diffraction limited field diameter for f/2 to f/10 scopes was - width_inches = 0.0007 * F^3 where F=focal ratio This works to the following for some common scopes at: In-focus sweet spot width F_ratio width_in width_mm %_1.25inFOV %_2inFOV 4 0.04 1 3 2 4.5 0.06 1 5 3 5 0.08 2 6 4 5.5 0.11 2 9 5 6 0.15 3 12 7 6.5 0.19 4 15 9 7 0.24 6 19 12 7.5 0.29 7 23 14 8 0.35 9 28 17 8.5 0.42 10 34 21 9 0.51 12 40 25 9.5 0.6 15 48 30 10 0.7 17 55 35 This also means that the fast mirrors scope have to be aligned within 1/10th of an inches or less or the image will degrade. Laser-aided collimation is a given. F/9 owners can drink heavily, horribly misalign their scopes by eyeballing and still have a passible image. -:) - Canopus56 __________________________________ Do you Yahoo!? Take Yahoo! Mail with you! Get it on your mobile phone. http://mobile.yahoo.com/maildemo

2 1

Orion discounts
by Patrick Wiggins 10 Feb '05

10 Feb '05

I just received this from the folks that just acquired Orion Telescopes. Patrick As a special benefit to users of Starry Night, we are offering a one-time savings on select Orion telescopes, binoculars and accessories. Act NOW to take advantage of this introductory offer! http://www.telescope.com/coupon.jsp?code=IMN0251&URL=%2Fjump.jsp%3FitemID%3… Imaginova (parent company of Starry Night and SPACE.com) recently acquired Orion Telescopes & Binoculars. In celebration of this new partnership, we are offering 20% off select Orion telescopes, binoculars, and accessories. To receive your 20% discount, please enter coupon code IMN0251 in the coupon code field of the Orion shopping cart (the coupon code field appears on the Payment Information page of the shopping cart). If the coupon code already appears in that field, you do not have to reenter it. Discounted prices will appear in the Orion shopping cart, but not on product detail pages.

1 0

RE: [Utah-astronomy] Question on focus
by Canopus56 10 Feb '05

10 Feb '05

David Dunn wrote, > I have seen this just looking at the moon itself. If > you are running much power, you will need to refocus > just to adjust for the curvature of the moon. If you are using a fast f/5-6 mirror, it may just be coma. The angular diameter of the in-focus "sweet" spot in the apparent field of view depends on focal ratio. The higher the ratio, the larger the in-focus sweet spot; the lower, the smaller the sweet spot. You usually do not notice the coma in deep sky fields because the dim stars do not provide a sufficient visual cue. The coma becomes easily seen with a large extended object like the Moon. For an f/9 mirror, the sweet spot can extend out to 3/4's of the apparent field of view. For a f/5-6 mirror in a DOB light bucket, the sweet spot may be less than 1/2 the apparent field of view. The coma problem inherent in fast f/5-6 light buckets is why the Teleview Paracorr "field flattener"/"coma corrector" is popular. http://www.cloudynights.net/lab/accessories/paracorr.pdf#search='corrector%20Paracorr' Suiter did a good article on the relationship between the size of the sweet spot to focal ratio in _Sky & Telescope_ in the late 1980s. I could not easily locate my copy but the article is referenced in the bibliography of Suiter's _Star Testing_ book. - Canopus56 __________________________________ Do you Yahoo!? Yahoo! Mail - Find what you need with new enhanced search. http://info.mail.yahoo.com/mail_250

3 2

Re: Re: [Utah-astronomy] OAS excursion to St. George
by astrodeb＠charter.net 09 Feb '05

09 Feb '05

Joe, The OIII filter is one nebula filter. The other one I have is a UHC nebula filter. You definitely want the OIII for planetary nebulae. You saw how it picked up the faint nebulosity in Abell 21. If I would of had more time I could have showed you the faint Jones1 in Pegasus before it moved west into the light pollution. Debbie > > From: Joe Bauman <bau(a)desnews.com> > Date: 2005/02/08 Tue PM 12:39:48 MST > To: Utah Astronomy <utah-astronomy(a)mailman.xmission.com> > Subject: Re: [Utah-astronomy] OAS excursion to St. George > > Hi Deb, it certainly was fascinating. You mentioned an OIII filter -- > is that the same as a nebula filter? I have a nebula filter and > probably should have used it! Best wishes, Joe > > _______________________________________________ > Utah-Astronomy mailing list > Utah-Astronomy(a)mailman.xmission.com > http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy > Visit the Photo Gallery: http://www.utahastronomy.com >

7 9

Re: Question on focus (Joe Bauman)
by Canopus56 09 Feb '05

09 Feb '05

Compare the smallest resolvable detail on the crater that occults Jupiter with the smallest resolvable detail on Jupiter itself - in the animated gif: http://skyandtelescope.com/largeimage.asp?img_url=/mm_images/7596.gif They are equally blurry or equally sharp. - Canopus56 __________________________________ Do you Yahoo!? All your favorites on one personal page Try My Yahoo! http://my.yahoo.com

1 0

Fwd: 3rd High Energy Astrophysics Workshop & Travel Grant Application
by Richard Tenney 09 Feb '05

09 Feb '05

--- aaronp(a)aavso.org wrote: > Date: Wed, 9 Feb 2005 14:49:24 -0500 > To: retenney(a)yahoo.com > From: aaronp(a)aavso.org > Subject: 3rd High Energy Astrophysics Workshop & > Travel Grant Application > > > Dear Club Leader, > > Would you mind sharing this information with your > astronomical club in a manner which is appropriate > (web > site, discussion list, newsletter, etc.)? Thank you > and > clear skies! > > You are all invited to the 3rd High Energy > Astrophysics > Workshop for Amateur Astronomers. > > When: March 21-23, 2005 > Where: New Mexico State University, Las Cruces, NM > Who: Sponsored by the AAVSO, NMSU, NASA Marshall > Space Flight > Center, and Sonoma State University through > the NASA SWIFT > and GLAST missions. > What: > The goal of this meaning is to educate the > public on > topics in high energy astrophysics. The focus will > be on > GRBs, magnetars, magnetic cataclysmic variables > ("polars") > and blazars. This is a great meeting for amateur > astronomers, teachers, students and grad students. > A lineup of high energy all stars is speaking > such as > Jerry Fishman, Lynn Cominsky, Arne Henden and Phil > Plait > (author of www.badastronomy.com) > Workshops will be held on high precision CCD > photometry, education and public outreach and an > introduction to data analysis using free Windows > software > tools. > A day-long field trip to the VLA is also > planned > (with a special tour for us, not the regular public > tour!). > Travel grants of $450 and $800 are available > to > residents of the U.S. and an application form is > already > online. Recipients of the travel grants are expected > to > share what they've learned with their local > community upon > return. How this is done can be creative (including > online > methods). Information is here! If you have any > questions > feel free to contact meetings(a)aavso.org. > Clear skies! > > Aaron Price > > > > > __________________________________ Do you Yahoo!? All your favorites on one personal page Try My Yahoo! http://my.yahoo.com

1 0

RE: [Utah-astronomy] Question on focus
by David Dunn 09 Feb '05

09 Feb '05

Joe, I have seen this just looking at the moon itself. If you are running much power, you will need to refocus just to adjust for the curvature of the moon. Now that I think about it, I have also seen it when viewing the Sun. Dave -----Original Message----- From: utah-astronomy-bounces+david.dunn=albertsons.com(a)mailman.xmission.com [mailto:utah-astronomy-bounces+david.dunn=albertsons.com@mailman.xmissio n.com] On Behalf Of Joe Bauman Sent: Wednesday, February 09, 2005 9:38 AM To: Utah Astronomy Subject: [Utah-astronomy] Question on focus Hi all, When I checked out the Sky & Telescope web site below (from Patrick's News), it had a great animation of the moon occulting Jupiter, on the third page. What I can't understand is why Jupiter is in sharp focus while the moonscape is slightly fuzzy. It isn't possible that there could be a real difference in focus between the two, I believe -- granted, Jupiter is thousands of times farther out, but for all practical purposes the focus for both should be at infinity. Or is it because the telescope was tracking on Jupiter, making it relatively stable, but the moon had some lateral motion for each exposure, causing blurring? Just curious. Also, if anyone has a minute, can you tell me why it's necessary to focus a telescope at all? You would think that, like an old Instamatic camera, everything beyond a few miles out would be at the "infinity" focal point. I know that's not true, but I do not understand why. Thanks, Joe

1 0