Help needed

[leo82]

Hi all,

last winter I had trouble focusing on stars and this year to kick things off the cat knocked my scope off the shelf in the shed!

I’ve taken this weekend time to learn collimating using the Cheshire, I used to use a cheap laser before.

Everything is all realigned and should be perfect now, but it isn’t.

I had a break in the clouds last night to test it out but it’s still only as good as it was last year.

I used Mizar as a star test, tried focusing on it with the standard 25mm eyepiece only to find just as it was starting to sharpen up the focuser barrel would fully unscrew and fall out of the helical focuser.

I read that doing a quick collimation on an out of focus star could help by tweaking the screws on the primary mirror. For this the star should look like a circle of rings all within each other when out of focus.

When I put Mizar out of focus all I could see was an outer circle and the vane of the secondary mirror.

The clouds came over and I’m still none the wiser at how to fix the problem.

The scope is a skywatcher heritage 130p. (I fully extended the trusses)

The best way to describe the view of the star through the eyepiece would be like a toddler trying to color in a circle.

Any help would be much appreciated.

The only thing that broke was the feet on the base and the red dot finder.

 

 

[Cornelius Varley]

I suspect what has happened when you recollimated the telescope the primary mirror has been moved closer to the secondary. If the primary is now closer to the secondary the point of focus has also been moved further away from the secondary, which means that you need to extend the focuser to compensate. Try recollimating the primary and move the primary lower down the tube.

[Buzzard75]

Peter's got it. Back both the primary adjustment knobs and the set screws out some so your primary mirror will sit lower in the tube. Even a fraction of an inch can make a huge difference in the focuser tube. Then recollimate and checking the focus again. If it still won't come into focus, then the other option is to get a focuser extension.

[leo82]

Thanks for the replies.

I will try again tonight and hopefully get a chance to test it out too.

Hopefully put an end to this headache!

[Astro Imp]

Another thing to check, have you extended the truss to the full extent?

[leo82]

I do fully extend the trusses each time I use it. I wish that was the problem, unfortunately, I know it’s not.

[leo82]

Well, I redid my collimating again last night but unfortunately it was to cloudy to test. However, I had a quick peak outside this morning and I could see just one star, right on the zenith, Capella I think it was.

i got my scope out and started focusing from the fully tightened up position and only had to undo about 5 turns to get it into focus!

Thanks again for your help, now I can happily use the scope again.

ps if I have one bit that’s not really that annoying but I could sort out would be that there seems to be a stray spike that comes out of the star at times, what could this be? 

Thanks again.

[Ricochet]

1 hour ago, leo82 said:

there seems to be a stray spike that comes out of the star at times, what could this be? 

 

That would be a diffraction spike caused by the single spider arm supporting the secondary. You can't get rid of it, but it should only be noticeable on bright stars.

[leo82]

4 hours ago, Ricochet said:

That would be a diffraction spike caused by the single spider arm supporting the secondary. You can't get rid of it, but it should only be noticeable on bright stars.

Ahh thanks for clearing that up for me, at least now I know it’s nothing I’ve done or could improve to get rid of it.