Celestron xcel

[Connorbrad98]

Hi I have a Celestron xcel 18mm Eyepiece anyway when I use this eyepiece in me skywatcher startravel 120 f5 the stars at the edge look very seagully astigmatic although I heard these Eyepieces are meant to be good at f5 could these "seagully" shaped stars be coming from the scope or is it just the eyepiece not being a good match for the scope?

[John]

Is the eyepiece the older X-Cel (top picture) or the newer X-Cel LX (bottom picture) ?

 

Apparently the more recent design is a better performer in a number of ways to the older design, including the control of the aberration called astigmatism which makes the stars towards the edge of the field of view that "seagull" shape you describe.

 

 

 

[Louis D]

Have you tried refocusing the edge to see if field curvature is the main culprit?  At 600mm focal length, I have to use a TSFLAT2 with my 90mm f6.7 APO to ensure stars are sharp to the edge.  Since your refractor is the same FL, I would think you need to use one as well.