The Curse of the Red Doughnut

[toryglen-boy]

Howdy

It seems anytime i take an image near any bright star, then i get a pale red doughnut for my troubles, i am pretty sure its the collimation marker on the primary, is there anyway i can avoid this? has anyone seen this type of thing before?

thanks

[renormalised]

I was going to say, is this another one of those cheesy Z grade Sci-Fi piccies:eyepop::P:P:D:D

[jjjnettie]

I get a big red doughnut on my moonage. I just cut the saturation right down to combat it.

[DavidU]

mmmmmm... of axis illumination of the mirror dot.
Can you replace the dot with a flat black dot of some kind?
Is the area inside the tube oppositr the focuser flocked well?

[gbeal]

Dunno, don't reckon it is the primary centre spot myself.
While I am only guessing at your sig, do you use the CLS in tandem with the MPCC, to me it is a reflection, slightly longer than focus, possibly from the filter?
Gary

[toryglen-boy]

Hi there

Yeah, i use them both together, do you think thats the cause? any idea on a remedy?

:help:

[DavidU]

Strongmanmike got some new type of filters that kept reflection under control.
I'll try and find the post

[DavidU]

Here is Strongmanmike's answer about low reflection filters
http://www.iceinspace.com.au/forum/showthread.php?p=465283#post465283

[toryglen-boy]

Thanks David

You're a gentleman


:thumbsup:

[gbeal]

Well, while the moon is about, try a trial of sorts, try a shot of the same field without either, then a shot with the filter only, then with the MPCC only.
That will give you four different shots to compare. Make sure the field is the same though, stars in relatively the same place. Don't worry about coma (no MPCC), or LP, (no CLS), just concentrate on the donut Homer.
Gary