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[Chicago Astronomer Joe]

Swapping out the stock focuser on the Celestron 102mm Refractor

19 April 2013

The Celestron 102mm Refractor that I got on clearance for cheap is doing a great job with my solar imaging. Light and with sharp imaging, it rides on top of the CG-5, (and prior on the CG-4) nicely...

A decent focuser came with the OTA, but as a rack and pinion type, it had some side-to-side/up/down slop, even with the tension screw snugged...

Focusing was another matter, as there is some gear lash on the R & P - making precise focusing somewhat tough. Having to go past the prime focus and returning numerous times. Doing solar imaging is tough as it is and with this added nuisance was really annoying me.

At one solar session I was getting really aggravated with the slop and cut up a plastic water bottle, using a piece as a filler. The built in ridges of the plastic really worked well and it stopped the side to side slop, but I still had to contend with the inherent poor focusing of the R & P. I have a dual speed Crayford style focuser on the C11...and focusing is a pleasure....totally eliminating the mirror shift and constant nose-on sharp viewing.

Time to swap this stock focuser out for a dual speed...for my sanity....

I researched around for a compatible replacement - balancing price with function. There were two candidates...

This one from a well known retailer was priced well...

Seems to be what I was looking for, but it looked kinda clumsy. Reviewers liked it though and it did do the job. The next one looked more inviting, although priced higher...

It's from the Chinese company GSO and as I have one on the C11, I am familiar with the build...

I liked the specs on this one better and the very cool feature of the 360 degree rotation of the focuser body. This will come in very handy when the scope is pointed at awkward angles. (With the stock focuser, I had the knobs all over the place - glad to be rid of that.)

The coast of the focuser is more than the scope itself!!!


But, I can always swap it out if I ever upgrade and the price of eliminating the aggravation is worth it. So I got it. The retailer had several sizes available and it was a best guess, after measuring the 102mm OTA - I got the 96.6mm (3.80") one.

It arrived in two days and well packed, with a baggie of attachment screws...

Not all that heavy (1lb 14 oz)

I dry fit the new focuser on my couch...as the workshop still has the C11 dis-assembled on the work shop table - and it's just too damn cold to work comfortably. The dual speed focuser fit perfectly and the attachment holes aligned!! Sweet...

The focuser draw tube is laser etched nicely and extends 3.11"...

The 2" body and the 1.25" adapter have brass compression rings...

Great that it won't chew up the diagonal sleeve like the old stock one did...

Looks hot... ;D

I lose the built in base holder on the stock focuser for a finder scope, but I can always attach one to the OTA when I take it apart for flocking and cleaning - when it get's warmer.

I will do some solar imaging soon with this new dual speed focuser and anticipate velvet-like focusing.

[Chicago Astronomer Joe]

First practical use of the new GSO focuser on the 102mm Refractor

20 April 2013

The day after I received the this focuser, the morning was bright, sunny...but very cold - for a late April day. I was anxious to try this new addition to the Chicago Astronomer arsenal out and some solar imaging is just the ticket.

The full solar session here:

astronomer.proboards.com/index.cgi?action=display&board=Observations&thread=4287&page=1

It does not throw the balance of the scope off at all and everything feels solid - even with the full assembly of camera, eyepiece and barlow.

Rack and pinion focusers have more of a draw tube run than do these roller bearing dual focusers do, so I hoped that I could get to focus before I ran out of drawtube. Starting to focus, I kept on drawing the tube out, and kept on and kept on...getting a little concerned that I might have to add an adapter collar between the OTA and focuser body.

But, with a few millimeters to spare, the solar disk came into sharp focus. Tweaking the smaller ratio focus knob, I brought the image into razor sharp focus...with ease...

Gone are the clunky lag filled days/nights of the rack & pinion focusing with the single knob - fighting with the mesh lag of the gears and getting frustrated.

It's only 1/4 turn of the smaller knob on either side to examine the best focus. The problem with' solar imaging, is that you are fighting with the atmosphere and one often gets a thick layer of turbulence between you and the Sun - making focusing difficult. But, then the air steadies and the image becomes a fleeting image of razor sharp detail...

I made use of the rotatable body, bringing the dual focus knobs toward my left hand while I shot picks with my right. (I was having trouble doing this before with the stock focuser.) Turning the knobs, smooth flow of the drawtube was appreciated. I had to snug the tension screw a bit, with the added weight of the camera & barlow on the 45 degree tilted scope.

Wind gusts were shaking the scope as well this day, but this shake out session for the new focuser was a good one and will make observing/imaging much more of a pleasurable one. I'll save the old stock focuser for a back up or maybe on the 90mm Meade refractor.

All scopes should come equipped with a dual focuser really.