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chuck1155
member
Reged: 08/21/09
Posts: 38
Loc: near Raleigh, NC
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Hello all,
I have no experience with refractors or GEM mounts. At my home I do NOT have a view to the north (street light in front yard). So can a GEM mount be polar aligned (for viewing only) without using Polaris?
thanks for the help.
chuck
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Z10 Dob
Nikon 10x50
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Jeff in Austin
scholastic sledgehammer
Reged: 02/26/07
Posts: 801
Loc: TEXAS
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Chuck,
Google "drift align" or "drift align telescope" and you have one solution. Some of the Celestron goto mounts have a polar alignment option in the hand controller that might help as well.
But first, use a compass and your local offset for magnetic North to get in the neighborhood.
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There's nothing like having a supportive family, including Second Grader w/ scope, curious toddler, and lovely wife.
Supporter of Austin CSC, Austin CalSky.
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mclewis1
Thread Killer
Reged: 02/25/06
Posts: 3938
Loc: New Brunswick, Canada
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The Celestron gems (CG-5, CGEM, CGE, and CGEPro) can all perform an All Star Polar Alignment so there is no need to be able to see Polaris. Have a look at the CGEPro manual link for the description of how this works.
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Mark
C11, C6, APM/TMB115, and AT80ED - Tandem mount CGE and CG-5A, WO EZ-Touch and AT Voyager
25x100s and 8x56s, T-Mount Light, Mark 1 eyeballs - Modded 350D, DSI-P, SPC900, Mallincam
Just because you can doesn't necessarily mean that you should
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Eric P
sage
Reged: 04/04/05
Posts: 390
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Yes. For a rough polar alignment you can use a compass to first locate the magnetic North, then adjust the mount to compensate for the offset of the true North from the magnetic North.
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Lane
Pooh-Bah
Reged: 11/19/07
Posts: 1494
Loc: Frisco, Texas
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From you question I don't believe you need polar alignment at all, you just need to be able to align for GOTOs.
And the answer depends on the GEM you buy - the hand controller software is really the key.
My CGEM will work even if you have a very limited view of the sky. This is because the Celestron Nextar hand control gives you a wide selection of alignment stars to use so you can always find one in the section of sky that is visible. It does not need to be polar aligned for visual work, you just aim it in the general direction of north and that is good enough. The GOTO accuracy does not depend on the direction the scope is aimed it only depends on having the mount level and centering the aligment and calibration stars properly in the eyepiece. On the other hand, tracking accuracy does depend on polar alignment so if you want the object to stay in the dead center of the eyepiece for 30 minutes then you need a pretty good polar alignment. But you can be pretty for off and the oject will still stay in the eyepiece for several minutes. Plus you can always use the arrow buttons on the hand control to keep the object centered. And as others have stated above, if do want to do a real polar alignment that can be done with the Nexstar hand contol via its All Star Polar Alignment software routine.
My Sirius mount with it Synscan hand controller is not so forgiving. To make the GOTOs work properly you need to be able to see polaris and get the scope aimed relatively close to it before beginning the alignment process. It also does not give you a very good selection of alignment stars so you need a pretty wide view of the sky to get it aligned.
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chuck1155
member
Reged: 08/21/09
Posts: 38
Loc: near Raleigh, NC
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Thanks for the guidance. i currently have a Z10 Dob and am thinking about adding a 4 or 5 inch refractor. i'm trying to decide on either the alt/az mount or the gem and that's what prompted my question. i'm old fashioned in many ways and would prefer using manual techniques without computer controlled goto system at this point in the hobby.
thanks again.
chuck
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Z10 Dob
Nikon 10x50
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Lane
Pooh-Bah
Reged: 11/19/07
Posts: 1494
Loc: Frisco, Texas
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I use to think that way too until I got a goto mount. Now instead of spending all night finding 20 objects, I have 3 choices:
1. Turn off the computer and spend all night finding 20 objects just for the fun of it.
2. Use the computer to find the 20 objects very fast and then spend a long time looking at them and drawing them.
3. Use the computer to find a couple of hundred objects in one night, some so faint I would never have found them without the computer.
And believe or not I have done option number 1 on several occasions. Just powered up the mount and skipped the alignment process. Then used the arrow buttons to scan around looking for things. So you don't really give up anthing when you get a GOTO mount or a Push-To computerized mount, you just give yourself more options.
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CGEM, ORION SIRIUS, AT Voyager
OTAs: C6, C8, C9.25, C11, Pronto, ED80
Orion 9x63, Fujinon 10x50 & 16x70
Ethos 13, 17 Nagler 9t1,12t4,16t2,22t4 Panoptic 27,35
Antares 1.6x, TV Powermates 2x & 4x, TV Barlow 3x, TV Plossl 8,11,13
Baader Hyperion 21, 8-24 Zoom, UO HD Ortho 6,7,9,12,18
TMB Planetaries 3.2,4,5,6,7,8, Pentax XW 10,14,40
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David Pavlich
Postmaster
Reged: 05/18/05
Posts: 8647
Loc: Mandeville, LA USA 30.22 X 90....
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For visual, all you need is a compass to get your mount pointed north. Do your star alignment and you're good to go.
If you do need to polar align and you can't see Polaris, you can try the iterative method.
David
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Proud Member; PAS NOLA,
"If we knew what we were doing, it wouldn't be called research..."
A. Einstein
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4933
Loc: MA
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No need to see Polaris (at least 1/2 the planet can't). Use a compass and local latitude to set up the mount. Done with a bit of care, it works fine for visual. If that's not good enough add a quick drift align. Celestron All Star polar align works great too, after starting out with a compass and latitude align.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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