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Help understanding CCDInspector results

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#1 Keudn

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Posted 20 November 2019 - 10:42 PM

Hi guys, 

 

I am trying to narrow down what is causing some issues with the curvature of my field at the edges of photos, so I popped 7 images from the same night and target into CCDInspector and this is what it resulted in. For reference, I am using a D5300 with my C80ED. The images were guided and were 360s at ISO-800.

 

 

2D Plot

3D Plot

 

The thing that immediately jumps out to me is the curvature. I know its a refractor, but do I really have that extreme of field curvature? What are the other metrics given in the 2D plot?

 

I also added 3 subs from a different target on the same night. Still 360s and ISO-800.

 

2D Plot

 

Why are these so drastically different?


Edited by Keudn, 20 November 2019 - 10:51 PM.


#2 Tapio

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Posted 21 November 2019 - 03:41 AM

While C80ED is relatively 'slow' scope you will benefit from reducer/corrector.



#3 sharkmelley

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Posted 21 November 2019 - 03:59 AM

 

I also added 3 subs from a different target on the same night. Still 360s and ISO-800.

 

2D Plot

 

Why are these so drastically different?

It's likely you had something like focusing tube sag or slack in the camera adaptor that caused sensor tilt for the image that reports a high value of the metric CCDInspector calls "curvature".

 

Mark


Edited by sharkmelley, 21 November 2019 - 04:43 AM.


#4 rgsalinger

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Posted 22 November 2019 - 10:51 AM

The first set are out of focus. The second set are closer to focus. You do have some tilt but for best results I'd do two things. First of all, get some spacers that thread into the focuser tube so that you only have to rack it out 1/2" or so to obtain optimal focus. Second, get a flattener or a flattener/reducer if they make one for your scope. I never use reducers because they also reduce that well corrected FOV which may or may not matter to you.

Rgrds-Ross


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