egg shaped stars

[pesa]

I have a problem with egg shaped stars wich I thought was collimation error, now I suspect mount but that doesnt seem completely logical either since autoslew doesnt report any position errors.

Therefor I wonder if bad balance (its far from perfect) cann reult in egg shapes even if autoslew doesnt report any errors?

pelle

[GeorgeCarey]

Are you guiding? Is the elongation of the star shapes always in the same direction?

[pesa]

^George,

^{I'm not guiding and when I look at images I see that the problem isnt the mount, or at least not only the mount.}

^{The images are consistent no matter direction (of scope) and vega at 0.001s showed eggshape as well.}

^{Every image shows eggshapes but direction of trail isnt totally uniform, But Close.}

^{My scope is ASA 10N astrograph.}

^{Main mirror is glued and doesnt move. Collimation is made with a tueblug+ glatters 2" laser. I dont Think I can improve upon collimation with those tools at least.}

^{This makes me wonder if the wynn Corrector (also asa) is defect, has that happened to anyone here?}

^{Sorry about the irregular capsm dont know why this forum editor does that.}

 

 

Also, anyone have an idea why I get so weird diffraction spikes?

 

pelle

[GeorgeCarey]

The weird spikes on Vega suggest something is wrong with the main mirror. That could also contribute to the egg stars.

If you aim at Vega and defocus what sort of image do you get? Is the result a circular disc?

[pesa]

George,

as round as seeing permits them to be (and that aint much!)

So not easy to judge from that.

I will move this question to astrograph section instead after I made some more thinking.

 

pelle

[pesa]

Come to Think of it, even if mount isnt part of the problem I'd like to know the answer to my original question:

Is there any situation (no guiding) when you have a good (enough) pointing model when bad shape stars resulted from ex. bad balance WITHOUT autoSlew reporting servo errors?

 

anyone?

 

pelle

[lukepower]

Pelle,

 

well, in theory one could have a bad pointing model - resulting from inaccurate data (shifting mirror, flexture and so on) - that could actually lead to elongated stars. Do you get the elongated stars only with long exposures or not? Let's say you make a 5 s exposure, and one with 60s: Are the elongations similar, or is the longer exposure different?

If they are similar, you have a collimation problem here (I could write a book about this, after struggling for months to get it right). If the short exposure is ok, you either have some severe flexure or a bad pointing model...

 

Autoslew won't report errors as long as it thinks it is driving the mount right.