Solar Limb Darkening - Forums

Topic starter

Dec 1, 2022 · Edited: Dec 1, 2022

Using my ASI178MM camera. I see some limb darkening on my photos, but it's not gradual. I see an area that looks like a border on the Sun but it's not all the way around the disk. When I rotate the camera the area rotates with the camera. I have 4 pictures that illustrates it better than I can explain it. I'm using SolarMax II 60MM telescope also. Using SharpCap to capture the image and the resolution is 2080X2080. Anyone have any ideas as to what may be causing this or how to eliminate it? Thanks for any suggestions

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Andreas Heertsch

Dec 10, 2022

First you have to decide: Camera or telescope problem:
is this grey segment connected to the sun? (Move focus a little, moves the segment the same way?)
If you defocus, will the segment also defocus?
If you change the gain, what does the segment?
If it moves allways it is probably a problem of the telescope (some aperture in or before the tubus?) Or your software manages contrasts partly in a wrong way in your picture.

dschenk952

Topic starter

Dec 11, 2022

Thanks for the reply. I will get back to you on the results. I'm thinking it is a telescope problem, Coronado has not responded.

dschenk952

Topic starter

Dec 14, 2022

Andreas Heertsch:
First you have to decide: Camera or telescope problem:
is this grey segment connected to the sun? (Move focus a little, moves the segment the same way?)
If you defocus, will the segment also defocus?
If you change the gain, what does the segment?
If it moves allways it is probably a problem of the telescope (some aperture in or before the tubus?) Or your software manages contrasts partly in a wrong way in your picture.

I went back and looked at some of my captures taken with a ZWO ASI 120 and the segment we're talking about is in them as well. Also I have some captures I've taken with the gain cranked way up and the segment is not in those photos. Looks like we're narrowing this down to a telescope issue. I'm disappointed with Coronado's support they have not responded. I'll try them again with this info also.

Andreas Heertsch

Dec 14, 2022

The SolarMax II has an Etalon: Try to move the frequency of the H alpha filter.
Does the grey segment show any changes?

dschenk952

Topic starter

Jan 8, 2023

Andreas Heertsch:
The SolarMax II has an Etalon: Try to move the frequency of the H alpha filter.
Does the grey segment show any changes?

No it doesn't change when adjusting the Etalon.

dschenk952

Topic starter

Feb 20, 2023

Update: I picked up a collimating eyepiece for refractors. Using it in the diagonal in place of the eyepiece there is the crosshairs do not line up with the center of the scope. I took the diagonal out and put the eyepiece in it's place and the crosshairs point to the center and I can see three clips like you would see if collimating a reflector. I took the Coronado diagonal out and put in a celestron diagonal and the crosshairs are on the center of the OTA.

Using a laser collimator with the celestron diagonal in the scope the laser is not evident and using a piece of paper to see where it is, it is in the center of the laser collimator. I put the Corronado diagonal in and the laser is visible on the face of the target.

With the diagonal out of the scope and the laser in it I spun the laser and the red dot circles the center, doing the same thing with the celestron diagonal the red dot from the laser stays in the center hole on the collimator.

This way the dot of the laser is behaving when it's in the Coronado diagonal explains why the shadow on the pictures rotates as shown in the pics I originally posted.

Looks like my diagonal is not aligned properly, I'm going to touch bases with Meade/Coronado and see what they say.

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