Post by Chicago Astronomer - Astro Joe on Jun 17, 2013 8:07:21 GMT -6
Scavenging a Polar Scope for the CG-5 Mount
17 June 2013
17 June 2013
The CG-5 mount does not come with a polar scope, silly really - and many feel that with the advanced go-to computer...doesn't need one. All one needs to do is a simple sight for Polaris athrough the empty tube, placing the star in the FOV...and the computer takes it from there....
During my past few test session, I did just that...and it does work somewhat - but a true alignment could be better with a polar scope from the start of the session.
At the start of this tread, pictured is Celestron's Polar scope for fifty bucks. Many other 3rd party resellers have it for $39.00 or so. I had contemplated getting one for awhile now, but why not try making one from parts I have around...?
Banging around is this very cheapo plastic finder scope, but it has somewhat ok optics, (for plastic lenses), and why not give it a try...
We examine the polar path and see what we got to work with here...
I loosen the set screws and remove the printed ring and lock collars...
Then remove the thumbscrew polar scope housing - (You can see the cheap Chinese glue-grease packed in there)...
...bringing us to the internal polar scope housing....
...which has spanner wrench indentations.
I try to remove this, with an assortment of tools, but it only moves about 1/2 of a turn despite many attempts. I leave it be and I can work around it. I lay my parts on the worktable...
The Thumb screw collar has these little pads to grab on the polar scope. I need to see what's going on at the other side of the polar sight, but the EQ head needs to come off...
I clean the parts and install the focuser eyepiece, (which I had to saw off), into the padded thumb screw collar...
...and just snug things for testing.
I then saw off the objective lens of the cheapo finder and shove it into the polar light path - which fits nicely into the bore...
I needed to find the proper focal range and spent about an hour looking at a distant chimney and adjusting the distance between the two lenses - and discovered.....I ain't digging it...
Although it sure could be used as a working polar scope, things are soft and it suffers from a bit of chromatic aberration. Yuk..... 
On to plan "B"...
I have used my CG-4 mount successfully for the past few years...which has a polar scope installed. I have polar aligned this mount with great success and it tracks well. I could use this polar scope in the CG-5...but I wonder if it's an easy swap or what? Online literature states that these are two different polar scopes for two different mounts...
But, some indicate that it fits both.
Well worth my time to try.
I remove the polar scope from the CG-4 easily and place the parts for examination...
And they need a cleaning.
I dis-assemble all parts - including the glass...which had dust and haze. I had a hell of a time blowing off all the minute dust particles, picking them off with solvent moistened Q-tips and repeating until the FOV was as pretty much clear as I was going to get it.
The Thumbscrew collar on this polar scope had a busted screw head....
Replacing it, I turn my attention to the Setting Circle, using the new one, as the old one from the CG-4 is a little beat up...
Putting it all together, it looks pretty good and all parts fit well without complaint...
Much better FOV clarity on the distant chimney with this one, but by the time I finished, the Sun had already risen and I could not do a Polaris test/axis adjustment.
The polar scope fit perfectly in the bore and no need to spend $44.00 to $50.00 on the designated scope for the CG-5 mount - or get an obsolete CG-4 polar scope at even a higher price tag.
I think this scavenge job will work well and help make tracking better and really...I like that a polar scope is on-board now....
