If you view a star at high power in good 'seeing' and rack the eyepiece from inside focus through focus to outside focus astigmatism will show as an elongation or ellipse whose long axis is mutually perpendicular inside and outside of focus. At best focus a cross replaces the Airy disc. Slight astigmatism shows as a thickening of the first diffraction disc at the points of a cross and would do little harm. If there is a problem I think you would have noticed it in use but check out a star. Even if the atmospheric 'seeing' or steadiness is only so so astigmatism should still be evident.
Would it not be worthwhile getting in touch with the retailer and ask him to do the right thing and replace the faulty scope? You wouldn't lose anything. It's an odd thing that it's the customer's responsibility to ensure that a new item is in good order and not the seller's. Especially if the customer is new to astronomy.
It's a shame that the law is so weak it allows customers to be cheated in this way.
But hopefully there are no ill effects and the crack remains stable in the future.
Hey, thanks, I notice astigmatism, BUT i believe it is my eyes, i don't even realized that i had and what astigmatism is until this event. When I in focus a star it appear elongated or straight like | then when i out focus it turn 90 degrees _ , when i turn my head 180 degrees though that line follow my turning direction. I have been using right eye most of the time, i was very surprised that my right eye show a straight line star and then when i change to left eye with the same focus, the star appear much less straight and much more round. This is all using 25 mm for my F5 telescope.
When i change it to 10mm, the stars become much more round and a much milder astigmatism for both eyes. I am waiting for 5mm lens to come, will try this out on this.
"At best focus a cross replaces the Airy disc" , I have not tried to observed more carefully on this, tonight if the weather permit, I am going to look for this.
But I am so new in this, this is my first time looking at stars via telescope, so I don't know what exactly the perfect view of a stars look like in telescope, there are some illustration in the websites, but illustration are not realistic, I been looking at some youtube video.
If my primary mirror has astigmatism, should it affect the view on planet too? Because the 3 planets Jupiter, Saturn, Mars looks very clear to me. At 150x magnification Jupiter I could see the belt and great red spot and Mars i could see the white polar ice.
Thank you, you have renewed my motivation that I shouldn't let them go that easily, I have just wrote to them again to help on this matter and still try to maintain good relation with them, there's consumer protection law here too, I prefer not to flex that muscle. They will get back to me on Monday again.
Edited by mandala8, 04 July 2020 - 05:09 AM.