? are these diffraction artifacts - visual observing

[JeremyS]

11 hours ago, Altair8389 said:

Hi Jeremy,

I had more attempts at the dobsonian. I found that the “diffraction flares at 120 degrees separation” lessened or disappeared on using a better eyepiece. I saw the concentric rings when I defocused on a star; perfectly (?) concentric circles, and I saw the typical 4 spikes at 90 degrees to each other like you see in photos or artificially generated by software. So my original problem may be due to low quality eyepieces and using glasses (specs). My left eye has significant astigmatism; to get minimal artifacts, use your best eye without glasses! 

 

Good tip about the Cheshire! I may have to try thinking getting a longer Cheshire tube! Previously I was confusing the 4 spider vanes with the Cheshire alignment hairs!
 

 

Good to hear you are making progress. Indeed try without glasses and with as good a quality eyepiece as you can (I’m surprised that even a low quality eyepiece could cause diffraction spikes/ flares tho). Perhaps you know someone who could lend you one.

Astigmatism is more noticeable at larger exit pupils, so try higher magnifications to see if the problem reduces  (and whether it is linked to one particular eyepiece)

[Froeng]

It is also worth rotating the head around the eyepiece. If the flares move with the eye, it is your eye’s astigmatism. If they stay put, it’s in one of the optical components of the scope…

Edited December 16, 2022 by Froeng