Celestron's CG-5 Mount
In the summer of 2003 Celestron began marketing its Advanced Series
telescopes, common to all available configurations is the latest version of the CG-5 tripod and mount system. I myself purchased the 8"
SCT system; a friend of mine purchased the 10" Newtonian system, a refractor configuration is also available. Celestron has been making a version of its SCT and placing it on a German Equatorial Mount (GEM) since the 1970s. The CG-5 has had a lot attention since it first became available; this latest version is no
exception. Although a very satisfactory mount it has had some growing pains.
For example, from first light the mount I owned was unpredictable
in its movements. Typically during one of its longer slews the mount
would inexplicitly jump to a high rate of speed and slew out of
control, or simple slew to an obviously incorrect position such as pointing at the ground.. Upon opening up the mount and examining the internal printed
circuit board it was obvious that the solder points for some of the
integrated circuits were coming into contact with the metal mount
housing. Celestron or its supplier knew about this problem since
several plastic covers or guards had been provided and placed over the
solder points. For my mount the plastic guards had moved and the solder
points had left scrape marks on the mount housing. I repositioned the
guards, and although this reduced the number of out of control slews it
did not eliminate them, ultimately the mount died completely. I assume
the plastic guards had shifted again and the printed circuit board had
shorted out. After the warranty repair I never had another out of
control slew with the mount, or strange GOTO position. One additional step I took was to purchase the mount interface cables necessary for upgrading the mount firmware, which I keep up to date. Recently I purchased a new hand controller, which allows for flash firmware upgrades. I would highly recommend this upgrade; I believe the new hand controller is easier to use than the old.
Preparing the CG-5's GOTO system for Observing
The following are the steps I take to prepare the CG-5 GOTO mount for visual observing, for astrophotography a more accurate polar alignment setup procedure should be followed. The first step I take is to level the mount, when I do this I use a compass
to roughly align the mount and tripod to where I think Polaris will
appear. Once Polaris is visible then the next step is to align the
polar axis, I believe that some users will rush through this step, do not! When
I first started using the CG-5 I would eyeball Polaris through the
mount, later on I purchased a polar axis finder scope from Orion, this
is the same unit used for their Skyview Pro Mount. After installing it
in the CG-5 and using it to do the polar axis alignment I found my GOTO
accuracy had improved. Once installed the polar axis finder scope is
easy to use, simply rotate the RA axis until the Big Dipper and
Cassiopeia are lined up with their images etched into the glass of the
finder scope. Next adjust the mount until Polaris is in the small
circle etched in the finder scope glass for it. I then return to the
level and recheck it making any necessary adjustments to achieve a good
level, any small error here will cause GOTO problems later. I then go
back and recheck the polar alignment making any small necessary
adjustment. Before I begin the calibration I pick out some distant
feature, a tree or hydro pole if it's not too dark or a distant light, I use the feature to line up the finder scope with the telescope. I have gone through several finder scopes, initially I used the as delivered 6x30 straight through finder, but it was too small which made it difficult for me to line it up with the calibration stars. I replaced the 6x30 with an Antares 8x50 right angle finder scope and Antares finder scope mount, it was better but I could never get use to the reverse view of the stars, so I replaced it with an Antares 7x50mm right angle image corrected finder scope. I disliked the Antares finder scope mount so I replaced it with an Orion finder scope mount, which is much easier to adjust than the Antares finder scope mount I was using. The best time to calibrate the GOTO system is before it's completely dark; as soon as Polaris is visible the likely calibration stars will also be visible. Once its totally dark it maybe hard to pick out the calibration stars. The first step in calibrating is lining up the mount index marks, I've always used the original as delivered index marks which means the telescope points about 8 degrees to the right of Polaris. I then enter local data such as time and location. The new hand controller has a US city database, it also allows for the entry of longitude and latitude through a custom location feature. I get my longitude and latitude information from a small hand held GPS unit that I use when I'm at some remote observing site. Usually I select the two star alignment, I might also include a third calibration star. I use two finders during calibration a red dot finder and the Antares finder scope.
When I first started using the CG-5 I found it very difficult to line
up the finder scope and telescope on the calibration stars, the red dot
finder solves this problem, a Telrad would also work well. All I have to
do is line up the red dot finder on the first calibration star and 99%
of the time that star is in the finder scope. Once the calibration star
is visible in the finder scope simply center it, press enter on the
hand controller and then center the star in the telescope eyepiece and
press the align button. I use a 20mm Plossl eyepiece for calibrating the mount although
to make it easier I have used a 40mm eyepiece. I have an extra eyepiece
with cross hairs that I have used if I want to be particularly accurate
in centering the star. I have found that the telescope selects good
calibration stars most of the time, when it does not it is because
something is blocking my view of the selected star, when this happens I
accept another star from the hand controller system. Once the star has
been entered I calibrate on the second star, I find that as a result of the first calibration star the telescope is more accurate and it usually has this next calibration star in the finder scope when the mount stops moving. I then repeat the alignment process. At this point the hand controller will ask the user if they want to add a third calibration star, this star is usually on the opposite side of the meridian with respect to the first two stars. I usually skip this step, I prefer to use sync stars during visual observing sessions. What is a sync star? Simple put it is any star close to an object of interest. For example if an observer wants to view M57, the Ring Nebulae, then an obvious sync star is Vega. Simply GOTO Vega, and select Align from the hand controller, scroll to the sync feature and select it, then follow the instructions for aligning the telescope with Vega. Once the sync operation is complete select M57 and you will find it centered in the eyepiece. For observing during a visual observing session most of the time I use a 14mm Meade UWA. 90% of the time after a GOTO the object of interest is centered in my 14mm if not I will switch to either a 40mm or the 20mm depending on how far off the GOTO operation is. For long slews from my sync star the 40mm and 20mm use increases. I can either Unsync, for example Vega, and select a new sync star near the object of interest or continue to use the 40mm or 20mm. Why not skip the two star alignment and simply do a one star or quick alignment and just depend on sync stars? I have found that the mount is just not accurate enough with respect to GOTO operations if just sync stars are used, unless the distance between the sync star and object of interest is small.
One final point, make sure you have a good power supply, for the first
few years I used a 19 Amp Hour jumpstart with few problems. Recently I
replaced it with a 10 Amp hour jumpstart, with poor results. I
discovered that the 10 Amp hour jumpstart could not supply a consistent
2 Amps of 12 VDC even though it was rated to do so. The result was poor
GOTO operations, which was really easy to misinterpret as a mount
problem and not a power supply problem. I switched to a 17 Amp Hour
system with 10amp fuses, the 10 Amp hour jumpstart had 5 amp fuses. The
GOTO problems went away immediately.