Confused

[stuck]

Hi all,

Can you help a newbie in distress please?

When I bought my 'scope (Celestron CPC 800) I got a "good" deal on a set of Celestron Plossl's ranging from the 40mm that came with the scope (the only one I've used succesfuly so far) down to 9mm.

If my math is correct a 9mm eye piece with a focal length of 2000mm for the scope would give me a magnification factor of 222x.

One of the primers I have read on this forum suggests that high magnification is good for viewing the planets, the moon etc.

Problem is if I use any eye piece <40mm (or by my math 50x mag) I can't even focus on the moon!

Please can someone explain what I'm missing please?!

Many thanks,

Mick.

[dweller25]

The SCT you have has loads of focus movement. Have you tried going fully clockwise and fully anticlockwise with the focus knob ??

[stuck]

Yes,

I've gone lock to lock as it were, at this rate I would have been better sticking with my toy shop refractor!

[Tim]

Sometimes you need a little extra distance to the lens, or reduce it a little.

How are you viewing? Through a diagonal?

[dweller25]

You done it right - but which eyepiece did you use - it's much harder to focus with the 9mm than with a 40mm.

[stuck]

Thanks for the replies.

I am viewing through a diagonal and have tried every eyepiece that I have but can only focus with the 40mm, I'm sure it's me and not the scope but haven't a clue what I'm doing wrong.

With a 40mm pointing at the moon the focus band seems to be about 1 turn, does it get much smaller as you up the power?

Mick.

[dweller25]

Mick, pop in the 40mm, line up on the moon then get correct focus. Then put in the next closest eyepiece you have and move the focuser clockwise - if the image of the moon gets bigger move the focus knob the other way until you hit focus, then try another eyepiece and refocus again - you will soon get a feel for how much focus change you need.

[Doc]

Try moving the eyepiece out of the focuser by about 10mm and see if you can focus then, if you can then you need an extention.

[stuck]

Thanks very much,

Assuming the cloud cover stays away tomorrow I will have another play.

Mick.

[Helen]

The only thing I can think of is that because the 9mm has a much smaller field of view you might not actually have the bright part of the moon in view when you're focussing. It happened to me. Because the moon was so bright the eyepiece was bright which made me think it was just a focus problem, but moving the scope a bit showed me I actually didn't have it in view.

Otherwise I suggest trying in daylight

Helen

[Tim]

Actually thats a good point Helen, I've done that many times

While using the 40mm, make sure the target is dead centre of the eyepiece. This gets critical when viewing things like galaxies and stars and globular clusters.

Have fun