Fuzzy Stars?????

[MarsG76]

Hi All,

I did a few nights of observing, something I missed doing for a long time but one thing I noticed every night is the fuzzyniess to the stars, especially the brighter stars. 

Would anyone have any idea why my stars are fuzzy when in focus... and I mean to the point where even alpha centauri is not resolved as a double unless I magnify it 185X and use a 15% ND filter. It's a lot worse in my 8" SCT than it was in a 60mm Tasco refractor.

Surely that is not how its supposed to be...

I did check the collimation and on Canopus using a 5mm Eyepiece and 3X barlow and it seemed to look ok... I'm sure that the stars used to be clearer.

Does anyone have any idea what I can do to clean up the views.

Thanks in advance,

MG

[spaceman_spiff]

Hi there,

Are the stars fuzzy across the whole field or only in the corners?

If not then there could be ghosting effects occurring because of the barlow lens.

Do you have a picture?

Happy holidays! 

[MarsG76]

I didn't take a picture, the stars are fuzzy across the whole FOV. It looks like a collimation issue, but the central obstruction shadow is dead center when i defocus the star both before and after the focal point. And the Corrector plate is clean too, so not something obvious, the corrector and mirror is clean.

[Peter Drew]

These effects are nearly always due to seeing conditions or optics that have not yet cooled to the ambient temperature. Try again on future evenings before resorting to tinkering with the collimation. 

[ollypenrice]

These effects are nearly always due to seeing conditions or optics that have not yet cooled to the ambient temperature. Try again on future evenings before resorting to tinkering with the collimation. 

Yes, bad seeing totally wrecks any attempts at fine resolution.

Olly

[Northern Soul man]

Hi  Ya MG, just have a look when your out next time, focus on a star fairly high up the sky, then as if your going to check collimation, de - focus the star and just have a look at the pattern, usually the "airy disc/pattern" which is created will show you the effects of tube currents and just a very unsteady atmosphere - it looks as though the outer brighter disc -  not the central one which shows the secondary "hole" with the bright dot right in the centre (if everything is collimated to a certain degree) will look like its bubbling and boiling - this bubbling and boiling effect is what we are all looking through - un equal tube currents and the atmosphere.  It gives the stars a certain "bloated" look - its just like you can't get a very good focus on the single point of light a star gives us - nothing to worry about.

I've always noticed this when looking through an SCT - some nights are much worse than others - you just don't get the "tight" star points like you do in a Newt or a Frac.

Paul.

[ronin]

Collimation, cool down or atmosphere.

Collimation you can check and adjust, they do need checking and setting at reasonably regular intervals.

Cool down is either patience or you have no chance - no chance if the temperature where you are is changing as the scope will be lagging behind all the time.

Astmosphere - really check the weather charts and see what is occuring, I guess there is a Southern jetstream is it over you, it it high or low pressure (high good), are the isobars well spaced out.

[niallk]

Hi I know what you mean It's a rare night (especially this year it seems) that I've had any better than rating 5 on this nice animated Pickering scale from Damian Peach:

http://www.damianpeach.com/pickering.htm

What I need to do is get out early in the morning for better still air - if the clouds, rain and humidity would ever shift!

Try and try again ... It's what makes a good night magical

Best of luck

[MarsG76]

Thanks for the comments, tips and help everyone..

These effects are nearly always due to seeing conditions or optics that have not yet cooled to the ambient temperature. Try again on future evenings before resorting to tinkering with the collimation. 

I'm going to try it on a "artificial star" placed at a distance... see if I can get a point

Yes, bad seeing totally wrecks any attempts at fine resolution.

Olly

Exactly, that is what is bothering me.. how much resolution am I losing because of this.

Hi  Ya MG, just have a look when your out next time, focus on a star fairly high up the sky, then as if your going to check collimation, de - focus the star and just have a look at the pattern, usually the "airy disc/pattern" which is created will show you the effects of tube currents and just a very unsteady atmosphere - it looks as though the outer brighter disc -  not the central one which shows the secondary "hole" with the bright dot right in the centre (if everything is collimated to a certain degree) will look like its bubbling and boiling - this bubbling and boiling effect is what we are all looking through - un equal tube currents and the atmosphere.  It gives the stars a certain "bloated" look - its just like you can't get a very good focus on the single point of light a star gives us - nothing to worry about.

I've always noticed this when looking through an SCT - some nights are much worse than others - you just don't get the "tight" star points like you do in a Newt or a Frac.

Paul.

I'm convinced that my collimation is spot on, as in I'm getting a symmetrical even disc with the obstruction secondary dead center with the point of light in the middle. I'll try the defocused trick looking for the currents/boiling effects as you stated... I did try focussing on Canopus which was very high in the sky, it was better than Alpha Cen but still FAR from perfect.

What about secondary mirror distortion?? I just remembered that my collimation screws are quite tight, as in they are near or at the extreme amount where they can be tightened to... could too much pressure on the secondary give a tiny bit of distortion to cause something like this too.. what I might do on a free day is make a artificial star, see if I can get a tight point of light that way, if not then I'll loosen the collimation screws and recollimate with the bobs knobs not being so tight.

Thanks for the responses every one I do appreciate it, this is just a new challenge for me to overcome... and I do have some ideas to try... 

The tube currents and scope not cooling is also a possibility since I did pull out the scope just before 1am and started observing straight away till about 3:30am... that is most likely the time I would need the setup outside for it to reach equilibrium... add to that that the temperature at this time here this time of the year was between 19-22 degree C... I guess the heat wouldn't help either. I'm just hoping that my scope transmission and reflective surface are not failing.. but I realize that this is quite unlikely.

MG