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Comet Hunter Mak-Newt Aberrations

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#1 janame

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Posted 02 August 2020 - 02:45 AM

I'm trying to set up an ES 152mm "Comet Hunter" Mak-Newt which I recently bought used.  I've got some aberrations I need to figure out am looking for advice about what's going on.  My previous experience with reflectors has only been for visual where I haven't been picky about dialing in performance.  I've been using a refractor for AP.

 

I've collimated the secondary with a cheshire and the primary with a barlowed laser.

 

I see three issues:

1) On the right side of the frame, stars are oval shaped and pointing toward the center.  On the left side, they're fine.

1-NGC6633-StarShape.jpg

2) Bright stars have blue and red "jets" coming out in opposite directions.  Effect seems to be significantly reduced in the center, and extreme toward the edges.

2-NGC6633-StarJets.jpg

3) Diffraction spike on a bright star centered in the frame, with bonus "jets" perpendicular to the spike, and a faint (but very large) concentric halo.

(See image in next post)

 

I know that the focuser drawtube can impinge on the light path if not racked out far enough.  I suspect this might be the cause of the diffraction spike.  I left the spacers on my camera, but will try again with those removed so I can have the focuser further out.  I don't expect this to be the cause of the jets or the oval stars, though.

 

Any thoughts on what needs tweaking here?

 

 



#2 janame

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Posted 02 August 2020 - 02:46 AM

Here's the diffraction spike:

3-Arcturus-diffractionSpike.jpg

 

And the full NGC6633 field here:

https://imgur.com/y6Guv13

 

I didn't take calibration frames, but I see I clearly need to take flats with this scope!


Edited by janame, 02 August 2020 - 02:52 AM.


#3 ks__observer

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Posted 02 August 2020 - 03:15 AM

Looks like chromatic abberation for colors.

Looks a slight tilt issue for lower right.

But curious what others say.


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#4 janame

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Posted 03 August 2020 - 02:40 AM

Looks like chromatic abberation for colors.

Looks a slight tilt issue for lower right.

But curious what others say.

What's tilted with respect to what?  The focuser and secondary?  Trying to figure out what I should be adjusting.



#5 ks__observer

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Posted 03 August 2020 - 05:59 AM

I believe you need to fix with a tilt adjuster.

I am plagued by similar stars.

https://www.google.c...tilt adjustment




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