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Back focus issue?

Stellarvue SVX130T Optolong L-Ultimate ZWO ASI2600MC Pro Flattener Coma
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NeilM avatar
NeilM avatar
Hi there!  I'm hoping that the kind experts here can help me analyze a small issue I am having.  I have slightly out of round stars in the corners of my images.  The images below show (in sequence):  center, top left corner, top right corner, bottom left corner and bottom right corner.  I also included the ASI Studio tilt analysis frame.

Do I have a back focus issue?  (or any other issues that you can see?)

My setup is as follows:
- Stellarvue SVX130T 
- Stellarvue SFFX1 Flattener
- L-Ultimate 2" Filter
- ASI2600MC Pro Camera
 
This is a single, uncalibrated, guided, 120-second image.  The bright slightly off-center  star is Phi Aurigae (magnitude 5)

Thank you!

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Bob Lockwood avatar
Bob Lockwood avatar
Could be the SFFX1 flattener you are using, as Stellarvue states that the SFFX3 should be used with SVX130T scope. The "3" is newer and may have a larger usable image circle.

Just a thought.
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NeilM avatar
NeilM avatar
Thanks Bob!

Definitely a possibility.  Vic from SV told me that the SFFX1 should be fine with the 2600MC camera because it is not a full-frame camera.  But worth exploring if that is the issue, thanks

Neil
Tony Gondola avatar
Tony Gondola avatar
Easy enough to find out if it is the flattener, shoot a few test frames without it.
Darryl Ackerman avatar
Darryl Ackerman avatar
I have the SFFX-3, ZWO OAG-L + ZWO EFW + 2600mono (55mm BF), stars are near perfect throughout the frame.
Brian Puhl avatar
Brian Puhl avatar
Darryl Ackerman:
I have the SFFX-3, ZWO OAG-L + ZWO EFW + 2600mono (55mm BF), stars are near perfect throughout the frame.



This comparison doesn't really help Neil much.   You would need a combined, RGB image of the corners, since his issue seems to be one of chromatic abberation.  His red stars will likely look perfect just like yours, but its his blue and green that are the issue.
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Darryl Ackerman avatar
Darryl Ackerman avatar
Here's the RGB, green and blue below. 

Green


Blue

NeilM avatar
NeilM avatar
My sincere apologies for the delay in responding!  Thank you so much Bob, Tony and Darryl for your responses.

I believe that in order to check for chromatic aberration, I should do another test without the L-Ultimate filter.  I know that the filter is most likely NOT adding to the chromatic aberration, but it is certainly changing the colors I see in the images.

I'll attempt to redo this test soon

Regards
Neil
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