EricJD
super member
Reged: 07/24/07
Posts: 112
Loc: Chesapeake VA
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My current setup is a Konus 120mm f8 refractor on a cg-5 clone mount. I'm taking photos with a DSI Pro, usually with a .5 focal reducer. I'm having a tracking problem. When I set up for 30 second exposures, unguided, roughly 70% of them turn out fine and the other 30% end up with star trails. From what I've read I believe this is most likely due to PE, but maybe I'm wrong in this. I also have serious backlash in DEC and a little bit in RA.
So, if PE is my problem, and if I'd like to get rid of the backlash, I've read that I can take this mount apart following the instructions on the astronomyboy.com website and get much better performance out of it by refurbishing it.
Here's the problem, I'm a mechanical idiot and am terrified of taking the thing apart and actually getting it back together in a working condition, let alone better off than before so I'm actually contemplating buying a replacement instead.
What would you all suggest? Give the refurbishing a go or try and save up to replace the mount?
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Orion 120mm @ f5
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BluewaterObserva
Post Laureate
Reged: 05/18/04
Posts: 4763
Loc: Zuni Mtns, NM
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I'd replace the mount. The EQ6 / Atlas is just so much more solid. the PE isn't all that much better on the spec sheet, but it slews heavy loads so much better, it is a ton better in general.
The next best mounts really start pushing the envelope.
Your description of your mechanical skills tells me you should NOT attempt the tune up.
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WarrenS
sage
Reged: 03/04/08
Posts: 313
Loc: Hudson Valley New York
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Atlas
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Warren
Astro-Tech 127EDT
Celestron Onyx 80ED
C8 (circa 1983 Orange Tube)
Atlas EQ-G
Canon 135mm F2.8
Canon 40D, Astronomik CLS clip filter
Leica, Minolta binos
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Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 2150
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I'd agree on the mount replacement idea, but if you decide to go that route, what harm would there be in getting your feet "greasy". Go ahead and attempt the rebuild. If it works, good for you. If it doesn't, you've got a pile of parts you might be able to sell used. If you don't attempt it, you've still got a pile of parts you can attempt to sell used, but they're pre-assembled. Either way, the resale value of the mount you have is only what you can get for it, and who knows what that will be. It may be less than the value of the experience you'll get by trying the rebuild.
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Steve Durham
www.margesmonograms.com
(Marge made me do it)
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Patrick
Postmaster
Reged: 05/16/03
Posts: 6778
Loc: Franklin, Ohio
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I suspect you have too much weight on the mount plus a long moment arm with a camera hanging off the end of the scope which doesn't help. It could be PE or it could be a little wind or vibration causing the trails.
If you're going to continue using the 120mm f/8, you might want to go with a beefier mount rather than investing money in a rebuild.
Patrick
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Discovery 10" f/6 Split Tube Dob
Celestron C6 SCT
Denk Binoviewers
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Oberwerk 9x60 Binocular
Celestron Regal 8x42 Binocular
Canon 30D DSLR
Mini EQ1
My Astronomy Pages
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RAKing
scholastic sledgehammer
Reged: 12/28/07
Posts: 803
Loc: Virginia
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Given your lack of mechanical expertise, I'm afraid I have to join the chorus and suggest a better mount. That refractor should be fine on the CG-5 for visual work, but you've got a lot of inertia and a long moment arm working against you for photography.
The Atlas would be the logical choice, unless you are ready to spend the big bucks (CGE, G-11, or A-P mounts). Mine works great for my visual observations with every scope I own.
Ron
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Time spent looking at the stars is added to your life.
"Hi Def" TV-102
C925-CF SCT "Time Machine II"
Orion XT10i / Moonlite CR2
GM-8 GEM / A-P Portable Pier
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EricJD
super member
Reged: 07/24/07
Posts: 112
Loc: Chesapeake VA
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Wow, I never thought that the scope that came with the mount would be too big. Thanks all for the great input.
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Orion 120mm @ f5
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Patrick
Postmaster
Reged: 05/16/03
Posts: 6778
Loc: Franklin, Ohio
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Quote:
Wow, I never thought that the scope that came with the mount would be too big. Thanks all for the great input
It's probably fine for visual...or at least okay. Manufacturers tend to push their mounts to the max of what the mounts can carry because of cost and pricing considerations.
Patrick
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Discovery 10" f/6 Split Tube Dob
Celestron C6 SCT
Denk Binoviewers
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Oberwerk 9x60 Binocular
Celestron Regal 8x42 Binocular
Canon 30D DSLR
Mini EQ1
My Astronomy Pages
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EWhytsell
super member
Reged: 06/15/08
Posts: 157
Loc: North Central Ohio
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The CG-5 is a very simple thing to take apart and put back together. There is really no reason you couldn't do it if you tried. Only 3 screws to get each drive assemblies plastic housings apart and then all you need is a basic set of allen wrenches and the screw driver you used to remove the plastic parts.
If your actually considering replacing it anyway you might as well give it a shot. The worst that could happen is that you crack the plastic or strip the holes the plastic goes in to and thats not gonna stop it from working. Mostly what you might wanna try is just tightening up the gears a little to see if that helps. This will be very easy for you to do.
If you want to give it a try you can PM me with any questions. In my real life job I repair everything from office equipment to cars and I build electromechanical things in my hobbies. I've taken apart my CG-5 lots of times and have even done it in the dark with just a red flashlight (hehe I was making field adjustments literally.)
Evan
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Classic C8 Super Polaris upgraded to CG-5 mount
Canon 40D unmodded
Edited by EWhytsell (08/05/08 08:08 PM)
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Jeff in Austin
professor emeritus
Reged: 02/26/07
Posts: 581
Loc: Austin, TX
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Eric,
If you do attempt to take it apart, take a few digital pictures before you take each part off. It's a big help with reassembly!
Also check to see if you have any play in the mount head. I've noticed my CG5 loosens up every 4-6 months, but I can tighten it up again once the plastic covers are off.
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Stellarvue SV102ED
Celestron C8-SGT XLT GoTo
Astro-Tech AT66ED
Canon 50D unmodded, TC80N3 timer, Stiletto Focuser.
DMK21AU04.AS
Coronado PST (Lunt LS60THa on order)
Supportive family, including First Grader w/ scope, curious toddler, and lovely wife.
Sponsor of Austin CSC, Austin CalSky.
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John Carruthers
Skiprat
Reged: 02/02/07
Posts: 1681
Loc: Kent, UK
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Hi Eric, is there anyone in your local AS who could buddy you for your first tune up? we have an instrument advisor, but most members help each other out too.
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Jc
ATM 10" F6.1, 1/25th wave spec (max wavefront error +/- 1/12.6 in zone 4 of 6, sodium light )
6" F7 spec
127mm F9.4 Refractor
10 x 50 bin
ETX80 (finder)
Canon 20D
and a curious mind
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EricJD
super member
Reged: 07/24/07
Posts: 112
Loc: Chesapeake VA
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Good call, I'll ask.
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Orion 120mm @ f5
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