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KovaK Planetarium
by Erik Hansen 11 Aug '13

11 Aug '13

" To be the director of a planetarium you need a college degree. If you build one they let you run it" http://www.cbsnews.com/8301-18563_162-57597945/stars-align-for-wisconsin-ma…

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Re: [Utah-astronomy] Image scale basics (WAS: Ring Nebula (M57) - Be prepared to squint)
by Joe Bauman 11 Aug '13

11 Aug '13

No, depending on which of these tubes you use, an SCT can be converted to either an f/5 or an f/3 -- meaning the magnification and scale are reduced more or less. What makes the difference is the length of the tube, not the addition of a lens. It works with my SCT but I don't think it would with a refractor. -- Joe http://www.optcorp.com/os-fr-1-25inch-focal-reducer-dual-f-3-and-f-5.html ------------------------------ On Sun, Aug 11, 2013 9:39 AM MDT Brent Watson wrote: >Joe, > >That would violate the laws of optics. Any telescope has a fixed focal length. If you move the film plane out beyond this distance then you are focusing closer than infinity. You can find that distance using the lens maker's formula. You cannot just place an extension tube in the path and get a larger image scale. > >Brent > > >________________________________ > From: Joe Bauman <josephmbauman(a)yahoo.com> >To: Utah Astronomy <utah-astronomy(a)mailman.xmission.com> >Sent: Saturday, August 10, 2013 5:22 PM >Subject: Re: [Utah-astronomy] Image scale basics (WAS: Ring Nebula (M57) - Be prepared to squint) > > >In the first illustration, no eyepiece is used. Note the small tube between the camera and the telescope. You can use a longer one, an extender, to get a larger image. I think you should be able to focus the telescope the telescope to accommodate the longer tube. -- Joe > > > > >________________________________ >From: Chuck Hards <chuck.hards(a)gmail.com> >To: Utah Astronomy <utah-astronomy(a)mailman.xmission.com> >Sent: Saturday, August 10, 2013 5:06 PM >Subject: [Utah-astronomy] Image scale basics (WAS: Ring Nebula (M57) - Be prepared to squint) > > >Here are a few illustrations and tables from Sam Brown's classic "All About >Telescopes" that are useful tools for making sure the object you're imaging >will be the size you want it in the frame. > >When the book was published, only film astrophotography was possible, but >it's all directly applicable to digital imaging. Your imaging chip just >takes the place of the film. The math is exactly the same. > >The first shows the 4 primary methods of telescope imaging. Note that a >refractor is used in the illustrations, but the type of telescope is >irrellevant. You can imagine the light cone coming from the objective at >left to be from any type of telescope desired, the camera doesn't care. > >http://i260.photobucket.com/albums/ii24/JethroTull1958/ATM/Imagingsystemsil… > >The next table will tell you the actual size of the object you want to >image on your chip or film, knowing your effective focal length. It's from >the pre-metric days, so you'll have to convert inches to millimeters. This >will tell you if you have sufficient image scale to show the object at a >satisfactory size. You need to know the actual dimensions of your chip to >know if the object will be too big or too small. > >http://i260.photobucket.com/albums/ii24/JethroTull1958/ATM/imagesizetable_z… > >This final table gives you the formulae to determine spacing with various >systems. This will help you decide which commercial extenstion tubes, >Barlows, adapters, etc., to order to suit your imaging system. > >http://i260.photobucket.com/albums/ii24/JethroTull1958/ATM/projectionarithm… > >Hope this is useful. >_______________________________________________ >Utah-Astronomy mailing list >http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy > >Send messages to the list to >Utah-Astronomy(a)mailman.xmission.com > >The Utah-Astronomy mailing list is not affiliated with any astronomy club. > >To unsubscribe go to: >http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy >Then enter your email address in the space provided and click on "Unsubscribe or edit options". >_______________________________________________ >Utah-Astronomy mailing list >http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy > >Send messages to the list to >Utah-Astronomy(a)mailman.xmission.com > >The Utah-Astronomy mailing list is not affiliated with any astronomy club. > >To unsubscribe go to: >http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy >Then enter your email address in the space provided and click on "Unsubscribe or edit options". >_______________________________________________ >Utah-Astronomy mailing list >http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy > >Send messages to the list to >Utah-Astronomy(a)mailman.xmission.com > >The Utah-Astronomy mailing list is not affiliated with any astronomy club. > >To unsubscribe go to: >http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy >Then enter your email address in the space provided and click on "Unsubscribe or edit options".

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Re: [Utah-astronomy] Image scale basics (WAS: Ring Nebula (M57) - Be prepared to squint)
by Joe Bauman 11 Aug '13

11 Aug '13

Yet another thought -- With my SCG I can change the scale depending on an extension tube's length without an eyepiece. That is because this type of telescope changes focus internally, rather than having a fixed focus like a refractor. But mostly I use a field flatener / focal reducer with tubes of a particular length. Hope that makes sense. -- Joe ------------------------------ On Sun, Aug 11, 2013 8:51 AM MDT Erik Hansen wrote: >> are not the function of telecompressors and teleextenders to change the >scale of photographs? I am no photographer but I thought that was what >Joe was originally referring to. > > > >Actually Joe, no, you can't change magnification in the direct objective >> configuration. >> >> The prime focus of any telescope focused for infinity is fixed. This is >> the focal length of the objective, or system in the case of a compound >> telescope such as a Cassegrain. Moving the camera further from the prime >> focus by means of extension tubes just puts the image out of focus. In >> other words, the camera chip and prime focus of the objective must >> coincide. Moving a focuser does not move the image. >> >> You CAN increase the image size by moving the camera further from an >> eyepiece when used in a projection system, number 3 in the illustration. >> >> Note that the primary image is in the same location relative to the >> objective in all three configurations. The camera moves to accommodate >> the >> shifted focus, dependant on configuration. >> >> The secondary mirror in your SCT is actually a reflective Barlow. It does >> the exact same thing in your telescope that a Barlow does in a Newtonian >> or >> refractor. It changes the focal ratio of the objective, lengthening the >> EFL of the sytem. While the light cone of your primary mirror is >> something >> like f/2, the light cone from your secondary mirror is that of an f/10 >> system. >> >> The small tube in the illustration is supposed to depict a focuser >> drawtube >> or camera adapter. It is not important to the diagram. >> >> Your SCT focuses by changing the spacing between the primary and >> secondary. Your prime focus moves according to the distance of the object >> under view. The closer the object, the further from the back of the >> telescope the image will be formed. But for objects at infinity, the >> focus >> is unchanged. The same thing happens with other telescopes; the focal >> plane moves further out, the closer the object under view is. But again, >> it's always in the same place for sky objects which are optically at the >> infinity position. >> >> >> On Aug 10, 2013 5:24 PM, "Joe Bauman" <josephmbauman(a)yahoo.com> wrote: >> >> In the first illustration, no eyepiece is used. Note the small tube >> between the camera and the telescope. You can use a longer one, an >> extender, to get a larger image. I think you should be able to focus the >> telescope the telescope to accommodate the longer tube. -- Joe >> >> >> >> _______________________________________________ >> Utah-Astronomy mailing list >> http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy >> >> Send messages to the list to >> Utah-Astronomy(a)mailman.xmission.com >> >> The Utah-Astronomy mailing list is not affiliated with any astronomy club. >> >> To unsubscribe go to: >> http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy >> Then enter your email address in the space provided and click on >> "Unsubscribe or edit options". >> > > > >_______________________________________________ >Utah-Astronomy mailing list >http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy > >Send messages to the list to >Utah-Astronomy(a)mailman.xmission.com > >The Utah-Astronomy mailing list is not affiliated with any astronomy club. > >To unsubscribe go to: >http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy >Then enter your email address in the space provided and click on "Unsubscribe or edit options".

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Ring Nebula (M57) - Be prepared to squint
by Dave Gary 11 Aug '13

11 Aug '13

Ring Nebula, M57. This has no more detail than viewing this feature visually through this scope. I couldn’t get any more detail because I wasn’t willing to invest the increased time on the exposures. These images are 4-minute exposures. You can see the mount was off a little. I kicked the mount by mistake while doing a fine focus. So much for good polar alignment. I don’t have an electric focuser for this little refractor. Wish I did. One question for anyone who knows or has experience with refractors: Does someone make a two-inch Barlow for a refractor that would allow the refractor to reach focus? I have a Zhummel 2-inch ED Barlow, but I do not have near the back-focus with this setup. Not even close. Is the solution, merely, to switch to the Schmidt-Cassegrain to use a Barlow? I don’t have enough experience with these things to know. I really like the little refractor for the tack-sharp focus (well, tack-sharp if you don’t trip over the tripod legs on a regular basis while acquiring an image). However, I’d like to have a slightly magnified image going to the CCD chip. What’s the solution? If this is a really stupid question try to suppress the laughter long enough to e-mail me back and tell me this is a really stupid question. Ask Patrick or Chris, it’s nearly impossible to hurt my feelings. Thanks, Dave http://www.flickr.com/photos/78046474@N06/sets/72157635009053182/with/94780…

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Thanks so much for the information
by Dave Gary 11 Aug '13

11 Aug '13

Chuck and Joe, Thanks so much for the information. I do have 1.25 and 2-inch extension tubes. I have a Celestron 1.25-inch Barlow, too. However, balance issues become a problem with increased length of the whole assembly. I’ve already nearly hit the tripod with the camera on near-zenith slews. The on-off switch for the mount is hard to find when you’re in a panic. I will go through those links you sent me, Chuck. Looks like there’s some excellent information in those pages. I’m bookmarking them, now. I think I’ll take the easier route for me and set up the 10-inch Meade when I want to manipulate the optical path. Also, Joe’s suggestion of taking shorter exposures and stacking them seems to be a viable alternative. Another learning session coming up. Darn, I was trying to avoid that. That Astro-Tech 8” carbon-fiber astrograph is looking better and better. Now, where to get the money to pay for it. Dave

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Dark sky
by Mark Shelton 10 Aug '13

10 Aug '13

Well it looks like it is going to clear here in tremonton. My wife and I have been here for a week golfing and camping. We are actually 10 miles north of tremonton. Very nice dark site. I will report on things tomorrow if the sky clears. Mark & Sallie Shelton Sent from my iPhone

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NASA webcast of the Perseids.
by Daniel Holmes 10 Aug '13

10 Aug '13

http://gizmodo.com/nasa-will-stream-the-perseid-meteor-shower-live-until-3-… Dan -- Daniel Holmes, danielh(a)holmesonics.com "Laugh while you can, monkey boy!" -- Lord John Whorfin

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Next ATM session
by Hutchings, Mat 10 Aug '13

10 Aug '13

This is a bit of a short notice, but the next ATM session is in a week. It will be held on 8/17/13 from 09:00 until 14:00 at the Hutchings' optical shop. Please let me know if you need driving directions and I'll send them to you. Take care, Mat

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Observing at Vernon tonivht
by Jay Eads 10 Aug '13

10 Aug '13

Mat and I are at a wonderfullg clear sky at FR 006 south of Vernon. Come out we are camping over. Jay

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Great Basin National Park Astronomy Festival - September 5-7
by Carroll, Kelly 09 Aug '13

09 Aug '13

Hello all, I would like to invite everyone to visit and volunteer this year's Astronomy Festival at Great Basin National Park in Baker, NV. The festival will be Thursday September 5-7, 2013. We will have activities all day and a star party each night. We would love if you would attend, and even more, if you'd volunteer to set up your equipment for the public viewings each night. As in the past, we will have the astronomer's camp, where volunteers can tent camp on the star party field, so you do not have to set-up and take down your equipment each night. We will have our annual astronomer's "Thank you" dinner Saturday evening. Please let me know if you have any questions and thank you for your support of this program. http://www.nps.gov/grba/planyourvisit/greatbasinastronomyfestival.htm *Schedule of Events* *Thursday September 5, 2013* 12:00PM - 1:00PM - Astronomy 101: An Introduction to the Night Sky 1:00PM - 4:00PM - Sun Viewing with Solar Telescopes & Solar Braclet Making 3:00PM - 3:30PM - Learn to Use a Planisphere with Dark Ranger Steve 7:00PM - 8:00PM - Ranger Talent Show 8:00PM - Kid's Deep Sky Certificate 8:00PM - Star Gaze with Astronomers and Telescopes *Friday September 6, 2013* 12:00PM - 1:00PM - Astronomy 101: An Introduction to the Night Sky 1:00PM - 4:00PM - Sun Viewing with Solar Telescopes & Solar Braclet Making 2:00PM - 3:00PM - Astronomy Presentation 3:00PM - 3:30PM - Learn to Use a Planisphere with Dark Ranger Steve 7:00PM - 8:00PM - Keynote Speaker Wally Pacholka Presentation 8:00PM - Kid's Deep Sky Certificate 8:00PM - Star Gaze with Astronomers and Telescopes *Saturday September 7, 2013* 12:00PM - 1:00PM - Astronomy 101: An Introduction to the Night Sky 1:00PM - 4:00PM - Sun Viewing with Solar Telescopes & Solar Braclet Making 2:00PM - 3:00PM - Astronomy Presentation 2:00PM - 3:00PM - Kid's Program - Discovering Light: Life in the Infrared! 3:00PM - 3:30PM - Learn to Use a Planisphere with Dark Ranger Steve 7:00PM - 8:00PM - The City Dark Film and premiere of "Great Basin Astronomy" Ranger Minute 8:00PM - Kid's Deep Sky Certificate 8:00PM - Star Gaze with Astronomers and Telescopes Kelly Carroll Park Ranger Great Basin National Park 775-234-7513 www.nps.gov/grba Experience your America Great Basin National Park Astronomy Festival - September 5-7, 2013<http://www.nps.gov/grba/planyourvisit/greatbasinastronomyfestival.htm>

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