Advice with problem on bright stars - Forums

Topic starter

Nov 30, 2021

Hello,

Can anyone give me some idea of what is causing these issues on my bright stars.

I know the image below is not perfect but the smaller stars are acceptable but I seem to get a half halo on the brighter stars...

Any help or suggestions would be greatly appreciated.

I am using a Skywatcher 130PDS. Could it be the alignment of the secondary mirror?

Thanks,

Joe

urban.astronomer

Nov 30, 2021

Joe,

I am not familiar with Newtonian scopes, but it looks to me as this might be an issue related to a tilt of the sensor.
https://aiastro.wordpress.com/2019/01/24/sensor-tilt-adjustment/

-Martin

Stjepan Prugovečki

Nov 30, 2021

Collimation ?

James Malone

Nov 30, 2021

I've also been investigating this issue on my RASA 8 too.

andrea tasselli

Frequent contributor

Nov 30, 2021

1 possible cause is decentered secondary, the 2nd is bright off-axis reflection (e.g. mirror holders). Shot one bright star centered in the sensor so that the fresnel pattern can be easily seen and we may rule out options.

Jeffrey Geiss

Nov 30, 2021

Also try shooting the bright star in all four quadrants of your sensor. If possible, try to recreate the error with an artificial star. Try to discern what orientation your sensor is to the optics. Rotate camera, does the error follow the camera or stay with the optics. Look at the optical path for anything that could cause reflection. Bare unflocked metal, a screw protruding, we even had an inch or two of a glossy glue used to fastened felt flocking in a dew shield cause a horrible bright star reflection. Is there anything in the optical path above the telescope, sorry I know seems obvious but a power wire on a pole or similar can distrubt light. After all that look carefully at any corrector lens filters or oag in optical train.

most important is seeing if the error follows a rotation of the camera and any device attached to it then yiu can start to narrow the problem.

Helpful

James Malone

Nov 30, 2021

Jeffrey Geiss:
Also try shooting the bright star in all four quadrants of your sensor. If possible, try to recreate the error with an artificial star. Try to discern what orientation your sensor is to the optics. Rotate camera, does the error follow the camera or stay with the optics. Look at the optical path for anything that could cause reflection. Bare unflocked metal, a screw protruding, we even had an inch or two of a glossy glue used to fastened felt flocking in a dew shield cause a horrible bright star reflection. Is there anything in the optical path above the telescope, sorry I know seems obvious but a power wire on a pole or similar can distrubt light. After all that look carefully at any corrector lens filters or oag in optical train.

most important is seeing if the error follows a rotation of the camera and any device attached to it then yiu can start to narrow the problem.

This is good advice. Many of these things are on my list, whenever Seattle finally has a clear night.

Well Written

Jeffrey Geiss

Nov 30, 2021

Ya I hear ya. South Carolina can be a sky swamp. Thats were the artifical star can help. If you have access to a long dark hallway, a long basement, someplace dark but long enough to allow system to come to focus. Mirrors can be used to extend that distance. There are Art Stars avail but you can make one. Ours using a piece of fiber optic cable, can buy a short one for a few bucks. Hot glue one end to a bright led. We use cheap PWM controllers to modulate brightness. This may allow you trouble shoot during day without wasting good clear dark skies fixing optical issues. Also goo to test back focus when adding new gear.

Supportive

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