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I recently tried imaging M7 with my 6" f/4 Newtonian. I had earlier commimated it with a Cheshire and Howie Glatter and was sure of the collimation. However, when I imaged using my DSLR with the coma corrector installed, I get focused stars off centre and not on the optical axis. Anyone experience anything similar before? What could this be? Tilt in the optical train? The focuser was drawn out only about 5mm to reach focus along with a 50mm extension tube. Any suggestion is welcome.

M7Offcentered coma.jpg

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Coma doesn't seem to be fully corrected either. Just a suggestion -the GSO CC spec I found online says 75mm spacing - I understand from the top of the CC lens to the camera focal plane. Is this how it is installed?

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19 hours ago, bobro said:

Coma doesn't seem to be fully corrected either. Just a suggestion -the GSO CC spec I found online says 75mm spacing - I understand from the top of the CC lens to the camera focal plane. Is this how it is installed?

Yes, to achieve the 75mm spacing, I have done the following.

1) 44mm from Canon DSLR flange to sensor

2) 11mm T-Ring

3) 20mm T-Thread extension rings.

I am assuming the coma corrector is slightly tilted. I have to verify it through tests.

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  • 3 weeks later...
On 06/09/2018 at 14:00, astrosathya said:

Yes, to achieve the 75mm spacing, I have done the following.

1) 44mm from Canon DSLR flange to sensor

2) 11mm T-Ring

3) 20mm T-Thread extension rings.

I am assuming the coma corrector is slightly tilted. I have to verify it through tests.

I'm having the same issue. Did you figure it out?

Edited by Anthony RS
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