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Seagull Shaped Stars

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#1 eoverstreet

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Posted 16 February 2020 - 08:38 PM

I found this picture on the Jerry Lodriguss webpage that best illustrates my problem seagull stars.  I was using FRAME and FOCUS in Sequence Generator Pro and failed to save a picture of my issues before clouds and drizzle begin and I had to close up.     

 

Gear used - Celestron Edge 8 HD, SCT telescope,  ASI1600MM-C Pro camera, ZWO filter wheel, with a  .70 Celestron focal reducer (made for this edge) and a Moonlite auto focuser.

 

Although my colliminaton was off before I installed BOB's KNOBS by almost the same amount as it is now....I did not have this problem then that I am having now.

 

The obvious problem with my kit points to poor collimation.  However, though I am certain it is out of collimation - the defocused star looks about the same now (after my most recent collimation attempt) as it did before I installed Bob's knobs.   Clouds and rain cut my attempt to improve on collimation but I will surely strive for a better collimation when they clear and that may fix this mess.  But - the collimation error before Bob's knobs is close to what it is now YET the stars before were good by not great before.....and now they are, as you can see, crazy seagull shaped.

 

So I am confused as to why I am NOW getting these stars?    I probably should have waited until I got a better collmation before posting this..... but my question is "could there be something else causing these seagull stars that I could be checking" as I feel like there is something else going on....and a better colliminaton may not be the fix.

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#2 Augustus

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Posted 16 February 2020 - 08:41 PM

IMHO Bob's Knobs are nothing more than a great way to lose collimation more often (they just aren't as secure as the OEM ones) and also tempt yourself to mess with it more often.


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#3 Cfreerksen

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Posted 16 February 2020 - 11:30 PM

It looks like collimation. Just wait for a clear night and spend about 15-20 minutes tuning it up. Bright star dead center. Adjust. Re-center. Repeat.

 

Chris



#4 Stelios

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Posted 17 February 2020 - 04:23 AM

Collimation, conceivably coupled with a heat plume effect, if the scope was still cooling when you took the images.

 

In any case, *first* fix the collimation (I recommend *this* guide and be anal about it--close only counts in horseshoes. Do the best the seeing will allow, and improve it on nights of better seeing. An Edge 800 ranges from a world-class-scope to a POS depending on collimation :))--and *then* worry about other things, if issues still remain.



#5 eoverstreet

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Posted 17 February 2020 - 07:59 AM

No sir...the kit is pier mounted - stays outside 365 days only protection , 360 Telegizmos....so temp issues are ruled out.  It is so obvious (since I had just installed Bob's Knobs) that it has to be collimation.   .......but since the collimation is not that far off now - why these odd stars.  The first chance for clear skies is this Friday.   But between now and then I plan to make an artificial star - never having done this sort of thing not too sure I can pull it off but the "fun is in the trying."

 

Thanks all for you thoughts on this.



#6 Augustus

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Posted 17 February 2020 - 08:47 AM

No sir...the kit is pier mounted - stays outside 365 days only protection , 360 Telegizmos....so temp issues are ruled out. It is so obvious (since I had just installed Bob's Knobs) that it has to be collimation. .......but since the collimation is not that far off now - why these odd stars. The first chance for clear skies is this Friday. But between now and then I plan to make an artificial star - never having done this sort of thing not too sure I can pull it off but the "fun is in the trying."

Thanks all for you thoughts on this.


Maybe something is off center. Either the lenses in the baffle tube or the corrector itself?

#7 eoverstreet

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Posted 17 February 2020 - 06:56 PM

I think I did a decent job of collimating the scope on a homemade artificial star.   Under an  8 power eyepiece it appears concentric and the dark spot in the center appears to be - dead on.   But I will not know for certain if these seagulls are history until I get a clear sky night....hopefully this Friday when the rain leaves....if not Friday then Saturday.  I did notice that when I went from focused to defocused (slowly) - about 6 wavelengths that I didn't see any gulls along the way...and then when I returned to focus and defocused in the opposite direction I didn't see them either.   

 

Fingers crossed!!  ..and thanks a bunch for everyone's help!



#8 Cfreerksen

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Posted 17 February 2020 - 06:57 PM

No sir...the kit is pier mounted - stays outside 365 days only protection , 360 Telegizmos....so temp issues are ruled out.  It is so obvious (since I had just installed Bob's Knobs) that it has to be collimation.   .......but since the collimation is not that far off now - why these odd stars.  The first chance for clear skies is this Friday.   But between now and then I plan to make an artificial star - never having done this sort of thing not too sure I can pull it off but the "fun is in the trying."

 

Thanks all for you thoughts on this.

You keep saying that it is "not far off". What make you say that? It is obvious that the star shape is not correct so how can you say it's not far off?

 

Chris


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