new scope??

[Wurzil]

hi all - my flatmate expressed an interest in buying another scope today. He had a 10" dob a year or two ago and ended up selling it as it was taking up too much space and it was hard to keep things in view (the scope was second hand and maybe needed lubricating or something).

So my question is - will an 8 inch SCT/MAK be ok on my manual CG-4 mount - im not sure of the payload tolerances for the mount or the actual weight of the OTAs such as the 8SE or an 8" MAK.

Also....where the hell can i find a second hand SCT now that the buy sell section has gone...what happened there??? Oh and how much should i expect to pay for a second hand one??

Thanks in advance guys

warren

[Cornelius Varley]

The Celestron 8 SCT weighs 5.67kgs, an 8" Maks will weigh nearer 10kg. I wouldn't put either of them on a CG4, both types of telescope will need at least an EQ5 or HEQ5 to support them. A CG4 mount will probably take a Celestron C6 SCT but it will be at the top end of the mounts payload capacity.

Peter

[Wurzil]

thanks for the weights and advice peter - so the 8" sct would be no good then??

Strangely I managed to find the weight of the refractor that came with the mount - which is also 5.67kg - surely the sct would be better as its shorter and will have less angular errr......thingy<insert proper scientific term>

http://www.celestron.com/astronomy/telescopes/celestron-omni-xlt-120.html

W

[Cornelius Varley]

Celestron have a habit of undermounting telscopes (ie C11 / CG5). The CG4 has a payload capacity of about 12lbs (5.44kgs), the closer you are to this capacity the less stable the mount becomes (the telescope will start to vibrate when touched and take longer for the vibrations to subside). I have a Intes Micro 603M which was originally mounted on a CG4, it was never a happy marriage, the telescope would wobble when touched and would take about 5 seconds for the vibrations to stop. The IM603 was then mounted on a HEQ5 Pro and the telescope was rock soild, any vibrations would subside in less than 2 seconds.

Peter

[Wurzil]

ahh I know what you mean then, about the undermounting- my setup does wobble (and does not like too much wind) - but im kind of used to it as its all ive known! I try not to touch the scope when im looking through then EP, and when im using the slow mo tracking controls i do so very gently and as slow as i can.

w

[jonathan]

I would consider a short tube refractor on the CG-4, there are plenty to choose from nowadays (depending on budget, of course). A long tube refractor may result in wobbles.

Or a 6SE as suggested, not sure if you can find these without the Celestron goto mount though. You could consider something from the Skywatcher range...

http://www.firstlightoptics.com/pro-series/skywatcher-skymax-150-pro.html

http://www.firstlightoptics.com/pro-series/skywatcher-evostar-120ed-ds-pro-outfit.html

as a couple of examples. Not sure what the Evo 120 weighs though.

[Wurzil]

Thanks Johnathon - i think more apeture will probably be the order of the day and as peter says the 8"SCT is is the same weight as the current scope currently mounted (omni xlt 120mm frac 1m long and 5.67kg). I might try and bully my flatmate into finding a second hand one of those, and then buy it off of him when he loses interest again!!

In all honesty I think the SCT idea will probably end up too expensive, so he'll end up getting another 10 or 12" dob

ps - Just checked the weight of the skymax 150 and its 5.6kg as well! It seems all telescopes weigh 5.6kg:confused:

Warren

[jonathan]

If you insist on putting a heavy scope on the CG-4 then you should be able to reduce wobbles by hanging weights in the middle of the tripod, if it's the thicker steel tube tripod that should help too, and you might get some benefit from anti-vibration pads. A dual-speed SCT crayford focuser should help too, as it requires only a feather touch for fine focus.

[Wurzil]

:DI can almost see you tutting and shaking your head at my abuse of the mount:D!!

Im basically looking for the largest apeture without going for a dob, on a small budget - which probably means re-using my CG-4. (It is indeed the steel tube one not the aluminium type btw)

TBH this is all blue sky stuff at the moment anyway, but i will definitely look into vibration pads and other tips to reduce vibration, when weighing up the options/price. In fact i could probably do with the vibration pads/hanging weights with my current set up so thanks for the tip.

Any idea what a 8"SCT OTA will cost second hand - i cant find one on ebay/astrobuysell??

W

[jonathan]

:DI can almost see you tutting and shaking your head at my abuse of the mount:D!!

It's not so much abuse as your ability to use it will be diminished, and thus your enjoyment of the scope you put on it, mostly due to vibration.

Any idea what a 8"SCT OTA will cost second hand - i cant find one on ebay/astrobuysell??

An 8SE new costs about £1200 with Goto mount. Without the mount, 2nd hand I would say the OTA might be worth about 300-400? The 8SE is a nice OTA on it's own, one that deserves a good mount (better than the Celestron Goto that comes with it). I have mine on an NEQ6 which is very nice, I don't think I would want to use it on anything less than an HEQ5 otherwise I may as well just use the Goto again (vibration hell!)

This may be why you don't see many 8SEs second hand - it gets re-mounted and kept by those who could not stretch to the CPC range. I had my reasons not to go for the CPC, I wanted to re-mount to an EQ mount from the start and the CPC design does not easily allow this.