Urgent help needed

[gazmass]

Hi

I have been looking at the skies for the last year with a Skywatcher Explorer 150. About two weeks ago a Celestron SGT 8" came on sale on ebay. I put in a little offer and was surprised when i won it! I have used it twice now but it will not focus. The first night I tired it would not focus and I put this down to dew inside the scope. Night I left if out side for quite a few hours and still got the same it would not focus on mars or the moon and it seems to have condensation in it.

The mirror seems fine and I hope it is because of dew it is not working I never had this problem with my other scope and so I am unsure what to do. Do I need to buy a dew heater and shield? Do i need to leave it outside longer or is there something wrong with the scope itself? I want to go to a star party tomorrow my first ever one and I am gutted I am missing Mars.

Thanks so much

Gareth

[ribuck]

Gareth,

I've never had a celestron but i did have a 10" Meade LX90 for a while and I never had any focus issues caused by dewing ?

What happens when you turn the focus knob?

it's probably worth pointing at a bright star and looking at the diffraction rings and see if they change when you move the focuser.

What eyepiece are you using for testing ?

Rich.

[MishMich]

Is it set up to use a camera, rather than visual? Or does it need a diagonal?

M.

[gazmass]

When I had my skywatcher I would find a planet and unfocus it so there was like a ring of light. I would then make sure that this was in the centre of my field of view and then when refocusing it would get smaller until the planet would appear. When doing this with my new telescope it starts to go down but it stops before the planet is in view. And it seems as though the focuser slips and you get a two rings like oo.

The moon is just a blur and will not show any detail. I have used my televue zoom piece on 12 and 24 and a revultion one at 32 it think i had in

[ribuck]

Have you checked the scope collomation ? it could have been knocked way out of whack in transit

[Hawklord]

Is there any point at which the image gets smaller and then bigger again? Or is it that on racking back the focus it gets smaller but never gets to the smallest size without reaching the rack's end of travel?

[yeti monster]

1st thing to check is collimation, it takes mere seconds to spot if it's miles out. If you have a collimation tool, then you can see how far out it is. After that start looking at any other reasons why the optics are not performing.

[gazmass]

Hawklord

It seems never to quite get to it's smallest size before reaching the end. It is almost within focus a few more turns but it can not go anymore.

ribuck

No I have not done that and i did wonder. I only did not try as my skywatcher seemed bang on straight away. I am not sure how to do it is there any equipment that i should get I know you can get the laser ones are these the best? Or which ones are

Also just wanted to say thank for your quick reponses and help

[Hawklord]

Are all of the bits that should be connected to the rear cell in place? Have a look at:

http://www.celestron.com/c3/images/files/downloads/1145296473_advancedsgt.pdf

Does it look like fig 2.10?

[gazmass]

yeah it looks like that hawklord

[SteveP]

That's a very unusual problem on an SCT. Their design provides miles of primary mirror travel for focusing - slight exaggeration! What diagonal are you using?

Steve

[Hawklord]

Hmmm. It doesn't sound like collimation, rather the mirror doesn't seem as if it's moving to its maximum travel. Beyond that I'm a bit stumped. There may be some more replies - dont give up just yet!

[Cornelius Varley]

Did you remember to loosen the mirror lock screws (page 32 of the instruction manual mentioned above?)

Peter

[John]

I suppose it's possible that the focussing knob has become detatched from the primary mirror - how old is the scope ?.

As has been said the SCT design usually has loads of focus travel.

[gazmass]

Yippee you have all made my telescope work!!!

I was looking at a bit in the handbook that hawklord gave me and saw in the focusing manual something about locking nuts for travelling. And then when Cornelius Varley said about it i went and found them out. There were four two was loose and the others were tight so I made sure they were all really loose and guess what it worked!!!

I am new to these telescopes so I had no idea they were there so I am sorry if it was a silly thing not to know. But i thank you so much for all your help I am so happy at seeing Mars and the moon. I will looking mainly tomorrow and can not wait.

Thank you all so much for all your help

Gareth

[kev 102 42]

Nice one Gaz really happy for you...................kev

[yeti monster]

Good-oh, now get some photons whizzing through it!

[Beyond_Vision]

Great to see you are up and running

Regards

Kevin

[TheThing]

Cool, well done.

[Hawklord]

Great news. Have a fabulous time at the star party.

[beamish]

Don't you just love 'appy endings ??

[Cornelius Varley]

It always pays to read the manual first.

Peter