First try with C8 SCT on CG5-GT

[rikyuu]

hi,

I recently got hold of a Celestron C8 SCT and CG5-GT mount of another member (thanks Phil!) and have been keen to try it out. The first thing I noticed about this kit is portability, especially compared to the 10" Newt and EQ6 mount I use to have, in fact the C8 and mount can be carried short distances together!

The C8 is much lighter than I expected, it can be easily lifted with one hand using the very rigid, piggy back camera mount. The OTA weighs only 5.6kg (the 10" Newt was over 12kg). The mount itself is relatively light again, about 10kg. (The head of the EQ6 alone was 15kg!).

The legs of the mount are huge and rock solid, being the 2" version. When I first extended them, I was wondering much more was to come out! It brings the mount up to a very good height for use with the SCT (or a refractor). I guess a Newt would be a bit too high at full extension.

I'd had a bit of a play with the mount and its set up in the house, I also have a Nexstar mount with similar functions so I'm fairly familiar with the control pad. On Tuesday night, I was just off to bed when I noticed the sky was clear. I thought this was my chance to try out the kit. It was in the loft, but it wasn't too much of a trauma to carry everything downstairs and outside. As it was pretty late, I just wanted to quickly check the function of everything.

I roughly polar aligned with the polar scope (ie. just set Polaris to the centre, nothing special), of course the clouds started to role in at this point so it was getting tricky to see Polaris.

I set the axis to the marker points and just did a one star align on Vega. It missed Vega by a degree or so, which I expected due to the quick setup. But once centred on Vega it stayed on target for a good period of time, even with a 6mm eyepiece, which is about 333x magnification. I did a quick 'out of focus star' collimation, which was made very easy due to the 'Bob's knobs' and short tube. It's possible to look through the eyepiece whilst adjusting the knobs. Very handy.

The noise of the slewing is quite loud, as everyone has said. I could just hear it in the kitchen, which is double glazed and about 3m away. Perhaps in the bedroom, it would be only just audible, but through an open window, it could be quite bad. I did add some sound dampening material around the motors and inside the plastic housings (as they act like boom boxes!). This improved it, but the noise need to be removed at source really, ie in the motor gear boxes. Due to their rigid mounting, the noise transfers to the whole mount. I believe from some (noise) experts, that packing gear boxes with grease normally helps (in general, not specifically Scope mounts), but the CG5 gears are fairly hard to get at, then there's the position sensors and electronics that wouldn't combine well with a coating of grease.

Moving on, the 10:1 focuser helps significantly, along with the rock solid mount. In fact even at this high magnification, there was barely any vibration as I focused and then honed in with the x10 reduction. There was some mirror flop, not sure how much I should expect, but at 333x mag, the object didn't go out of the FOV.

At high magnification, Vega was shimmering badly, of course I hadn't let the tube cool down and I was viewing though some patches of fairly thick cloud by then!

With a 25mm standard issue SW eyepiece, the view was quite pleasant.

I decided on a quick GOTO to M57, which fell easily within the FOV. Here, the 200mm apeture helped out (compared with my 80mm refractor). M57 was very apparent (in the gaps in the clouds). With averted vision, the central hole and ring were very clear. With the 6mm eyepiece, it almost filled the FOV! But of course it was very fuzzy.

Now it was definately time for bed and had clouded over completely.

So a good initial test all-in-all. I'm very pleased with the portability and ease of setup. Noise is a definate down side, but manageable.

I have a F/6.3 reducer/corrector on it's way, so I am looking foward to some imaging after moving house (to a darker site, but not just for that reason!).

Cheers

[red dwalf]

nice setup, good price, you just pipped me to the post on buying this one from Phil, but i managed to get a cg5-gt with a 6" celestron sct over the weekend but haven`t had chance to use it yet due to the poor weather.

mount is alittle noisey when slewing at top speed but i found if you set it to slew at a slower speed i.e. 6 or 7, the noise reduces quite a bit.

[John]

That looks a very nice setup - thanks for the report !.

I'm pleased that the CG5 seems to have decently long legs - I'm thinking of one to use with a refractor and I don't want to have to lie on the ground when viewing the zenith area !.

Nice scopes C8's - I had my best ever views of Saturn a couple of years ago through one - simply superb.

You do need to keep them well collimated though - with the largish central obstruction contrast and resolution decline quickly with a bit of mis-collimation.

John

[philsail1]

Very pleased that you are liking the set up and are getting some quality use out of it "rikyuu"

Nice first light report too.

Best wishes for some clear nights.

Regards,

philsail1

[rikyuu]

Thanks all, had a couple of good nights with it now and managed a few photos last night. The f/6.3 focal reducer/corrector came today (Hirsch) so something else to try.