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Causes of field curvature in an ag optical idk telescope

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7 replies to this topic

#1 whirlpoolm51

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Posted 29 September 2022 - 09:34 PM

So I’ve been through the ringer with this scope since I’ve got it , it’s a 14.5” idk

Shouldn’t be this hard but as luck would have it it is for me lol

Here what I’ve done so far

Collimation using sky wave ( comes out perfect every time)
Dave has had the scope back and gave it the okay nothing wrong with it

Ron at moonlite checked nitecrawler focuser and it was dead on

I do have some focuser tilt as the laser doesn’t hit the center spot without tilting

I have tried collimating with and without tilting the focuser to no avail

Tilt adjustments using ccdi and hocus focus

No matter what I do I still end up with elongated stars in all different directions

Top left - major axis pointing center
Bottom left - flat stars minor axis pointing towards center
Top right - major axis center
Bottom left minor axis center

There is no pattern to it at all nothing that says backfocus is wrong or anything

Tilt in ccdi when I get it to 0 still shows 30% curvature and I still have elongated stars in corners

What in that holy crap could be wrong!!!???

Any ideas please , pretty please!! Would make my life so much better haha I feel so defeated and it’s been 2 months and so many clear nights gone

I have to get this!!!

#2 barrett_flansburg

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Posted 29 September 2022 - 10:16 PM

I don’t have an iDK, but I would ask what your exact image train is. 
 

Focuser (Nightcrawler) followed by OAG (model?) followed by filter wheel (model?) followed by camera (model?) or something else?

 

My guess would a combination of tilt and backfocus. Can you add and/or subtract a millimeter from the backfocus to see what happens to the star shapes?

 

Hopefully someone with a similar scope and image train can chime in. 
 



#3 whirlpoolm51

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Posted 29 September 2022 - 10:33 PM

It goes nitecrawler , 2” , 1” and 1/2” spacers that came with nitecrawler to a m68 to wr35 adapter , connected to a zwo large OAG which is bolted directly to the filter wheel and the camera is bolted directly to that

I’ve also tried removing all of that and just using the camera and got the same results

The corrector is integrated into the scope so back focus is felt with by moving the mirrors closer or further apart a little

AGO has the back focus at 10.45” and mine is at 10.25
Dave at ag optical says if it’s within + or - 25 I’m good to go

I still suspect some of the issue is back focus but my stars look horrible off axis out of focus

I’m literally at the point where either I pay someone to look at it or sell it lol

#4 whirlpoolm51

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Posted 29 September 2022 - 10:37 PM

I’ll post some data tomorrow I give up tonight lol it was another night of failure

#5 akulapanam

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Posted 30 September 2022 - 09:22 AM

Sounds like you have a spacing issue. Are you sure mirror spacing is correct? You should be able to use starwave or a roche eye piece to check.

#6 whirlpoolm51

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Posted 30 September 2022 - 11:57 AM

Ya know , I have a gerd Neumann photographic ronchi that I tired but I could never get it to work!! Could only see half stars almost like my focal plain was so tilted it wasn’t able to pass through the grating

#7 sharkmelley

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Posted 30 September 2022 - 06:21 PM

Is there a possibility of sensor tilt?



#8 whirlpoolm51

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Posted 30 September 2022 - 06:46 PM

I’ve used both a 2600mm pro and 268m and they both gave me the same results lol what are the chances??

Ron from moonlite gave me his focuser tilt plate and camera plane adjuster and I’ve tried it but ran out of adjustment on the camera plane one


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