CG-3 Equatorial Mount

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Doodlebug
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CG-3 Equatorial Mount

#1

Post by Doodlebug »


What sort of realistic exposure times can I expect to manually guide with the CG-3 mount assuming my polar alignment is good?
I know it's an inexpensive mount, but it is all I could afford at this time.

Thanks,
--Shawn
-Shawn

Equipment:
Scope: Astro Tech AT72EDII, William Optics 50mm Guidescope
Mount: ZWO AM5, AZ GTI
Guide Computer: ASIAIR Mini
Finder: Astro-Tech Illuminated Multiple Reticle Finder
Diagonal: William Optics 2" 99% Dielectric Dura Bright Carbon Fiber Mirror Diagonal
Barlow: Celestron X-Cel LX 1.25-Inch 2x Barlow Lens
Eyepiece: SVBONY SV135 Eyepiece 7 to 21mm 1.25 Inch Zoom
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Richard South Africa
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Re: CG-3 Equatorial Mount

#2

Post by Richard »


Well manually drive for AP must be really hard , perhaps the moon and some planets at most , but a motor drive for these mounts are quite cheap so if you really want to do AP then get one I assume you will be using the 71mm Refractor , but if you put a big camera on ?
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Re: CG-3 Equatorial Mount

#3

Post by chris_g »


With a decent polar alignment, maybe 10 seconds before you start to see drift. With a perfect polar alignment, 30 seconds before you start to see rotation in the field.

If you can find one in stock, motor drives aren't that expensive for that mount. Would help to know what your going to have riding on the mount though...

https://telescopes.net/93515-motor-driv ... ounts.html
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Re: CG-3 Equatorial Mount

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Post by Doodlebug »


chris_g wrote: Thu Aug 18, 2022 2:49 pm With a decent polar alignment, maybe 10 seconds before you start to see drift. With a perfect polar alignment, 30 seconds before you start to see rotation in the field.


If you can find one in stock, motor drives aren't that expensive for that mount. Would help to know what your going to have riding on the mount though...

https://telescopes.net/93515-motor-driv ... ounts.html
I'm already looking at the motors, next on my purchase list.
10 seconds is about what I was hoping for, thanks so much!
I will be using my AT72EDII and a Panasonic G9 or GF3
Might also just use it for viewing.
--Shawn
-Shawn

Equipment:
Scope: Astro Tech AT72EDII, William Optics 50mm Guidescope
Mount: ZWO AM5, AZ GTI
Guide Computer: ASIAIR Mini
Finder: Astro-Tech Illuminated Multiple Reticle Finder
Diagonal: William Optics 2" 99% Dielectric Dura Bright Carbon Fiber Mirror Diagonal
Barlow: Celestron X-Cel LX 1.25-Inch 2x Barlow Lens
Eyepiece: SVBONY SV135 Eyepiece 7 to 21mm 1.25 Inch Zoom
Camera ZWO 294mc Pro, ZWO 120mm Mini, Panasonic G9
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Re: CG-3 Equatorial Mount

#5

Post by Baurice »


Doodlebug wrote: Thu Aug 18, 2022 5:32 am What sort of realistic exposure times can I expect to manually guide with the CG-3 mount assuming my polar alignment is good?
I know it's an inexpensive mount, but it is all I could afford at this time.

Thanks,
--Shawn
You don't mention which camera you have. You also need to know the focal length of your 'scope and this includes any Barlow lenses you have.

For objects near the celestial equator, the exposure time is about 500/focal length without guiding for a DSLR. Some advocate a more pessimistic figure but that seems to work for me, in practice.

If you are near the celestial pole, you can divide that figure by the cosine of the declination, which suggests infinite exposure time !! at the pole. However, if your field of view is (say) 10 degrees, you need to find the cosine of 85 degrees (90-10/2).

I do not hand guide and do not have a motor drive but I like to think I can get a few decent photos but I don't get the REALLY difficult stuff, like the Horsehead.

As an example, here's a recent shot of the Pleaides, without a telescope but just a zoom lens with a DSLR.

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Re: CG-3 Equatorial Mount

#6

Post by SkyHiker »


Doodlebug wrote: Thu Aug 18, 2022 5:32 am What sort of realistic exposure times can I expect to manually guide with the CG-3 mount assuming my polar alignment is good?
I know it's an inexpensive mount, but it is all I could afford at this time.

Thanks,
--Shawn
Check the rule of 500. For your 430 mm focal length that's about 1 second without RA motion. If you turn the RA control manually you may get trails from the motion of your hands. With astrophotography, a loose hanging cable can already cause problems. See what you can get but have modest expectations.
... Henk. :D Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: CG-3 Equatorial Mount

#7

Post by Doodlebug »


SkyHiker wrote: Sat Aug 20, 2022 2:49 am
Doodlebug wrote: Thu Aug 18, 2022 5:32 am What sort of realistic exposure times can I expect to manually guide with the CG-3 mount assuming my polar alignment is good?
I know it's an inexpensive mount, but it is all I could afford at this time.

Thanks,
--Shawn
Check the rule of 500. For your 430 mm focal length that's about 1 second without RA motion. If you turn the RA control manually you may get trails from the motion of your hands. With astrophotography, a loose hanging cable can already cause problems. See what you can get but have modest expectations.
So the longer the focal length, the higher the magnification and the shorter the exposure without trails.
My expectations aren't very high at the moment. I get excited when a satellite zips by.
I spent a few hours just locating and verifying targets tonight. (Stellarium is my friend)
Thanks so much for taking the time to respond,
--Shawn
-Shawn

Equipment:
Scope: Astro Tech AT72EDII, William Optics 50mm Guidescope
Mount: ZWO AM5, AZ GTI
Guide Computer: ASIAIR Mini
Finder: Astro-Tech Illuminated Multiple Reticle Finder
Diagonal: William Optics 2" 99% Dielectric Dura Bright Carbon Fiber Mirror Diagonal
Barlow: Celestron X-Cel LX 1.25-Inch 2x Barlow Lens
Eyepiece: SVBONY SV135 Eyepiece 7 to 21mm 1.25 Inch Zoom
Camera ZWO 294mc Pro, ZWO 120mm Mini, Panasonic G9
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Re: CG-3 Equatorial Mount

#8

Post by OzEclipse »


I started in astronomy in 1978. When I had my first try at astrophotography, hand driving the worm via a flexible cable was the only way. It is possible, although very hard work. We used the cross hair eyepiece out of the finder scope in the main scope with the camera and lens piggybacked. We defocussed the star until 4 little defocussed quadrants poked out from behind the crosshairs. Then we kept the four quadrants, the same size with slow continuous movements of the cable drive. Using 1970's film, our single exposures were 1 hr long. I'm sure you can do a few 2 min exposures with your DSLR. You can buy a motor drive for that mount but the periodic error is quite large on that mount. Use shorter focal length lenses eg 50mm.
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Re: CG-3 Equatorial Mount

#9

Post by Baurice »


I second the 1 second exposure time that you can get with your telescope but remember that it increases as you move from the celestial equator. An object at 50 degrees north would deliver an exposure time of 2 seconds. The cosine of 60 is 0.5, so 1/0.5=2.

Also there is stacking where you use Deep Sky Stacker (FREE!!!) or similar to combine multiple exposures into a single image.
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Re: CG-3 Equatorial Mount

#10

Post by Doodlebug »


While using the CG-3 the other day on terrestrial objects, I noticed the RA was not working properly.
Upon further inspection I noticed that the gear was stripped in multiple places.
I threw the mount in my closet until I have time to take a good look at it.
I then went searching for a new mount to fit my miniscule budget.
I raided the couch cushions and shook the dryer to raise enough to purchase a new mount.
I have decided to go with an AZ-GTI for the time being.
I placed the order this morning and will be looking forward to its arrival.
Thanks for all of the help with the CG-3.
I am sure I will have questions about the AZ-GTI.
-Shawn

Equipment:
Scope: Astro Tech AT72EDII, William Optics 50mm Guidescope
Mount: ZWO AM5, AZ GTI
Guide Computer: ASIAIR Mini
Finder: Astro-Tech Illuminated Multiple Reticle Finder
Diagonal: William Optics 2" 99% Dielectric Dura Bright Carbon Fiber Mirror Diagonal
Barlow: Celestron X-Cel LX 1.25-Inch 2x Barlow Lens
Eyepiece: SVBONY SV135 Eyepiece 7 to 21mm 1.25 Inch Zoom
Camera ZWO 294mc Pro, ZWO 120mm Mini, Panasonic G9
:Astronomer1:
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