Focus issue post cleaning

[Littleguy80]

Just given my dob a test run following cleaning the primary mirror. I can’t get stars into focus. They appear stretched out vertically coming to the focus point and then stretch out horizontally as it passes the focus point. I’ve obviously not got it back together quite right. I did struggled a bit with collimating the secondary. Does this sound like bad collimation on the secondary? Or is there another explanation? Any suggestions appreciated! 

[alanjgreen]

Neil,

you are describing astigmatism.

Check the mirror clips and make sure it is not in too tight. 

 

Alan

[Littleguy80]

6 minutes ago, alanjgreen said:

Neil,

you are describing astigmatism.

Check the mirror clips and make sure it is not in too tight. 

 

Alan

Thank you, Alan! I did do them up quite tight. Hopefully that’s it!

[Saganite]

Alan is correct Neil, the mirror should be able to just move under the clips, with the slightest of gaps.

[Littleguy80]

3 minutes ago, Saganite said:

Alan is correct Neil, the mirror should be able to just move under the clips, with the slightest of gaps.

Thank you! I definitely went too tight then. Will report back shortly after I’ve adjusted and recollimated!

[steppenwolf]

Neil, you could try placing the mirror clips with a piece of this card between the clip and the mirror surface then remove the card thus leaving a small gap to avoid pinching the mirror.

[Littleguy80]

All sorted. I had no idea that the primary should be able to move under the clips. Every day is a school day  Although my first thought when I saw what was happening through the eyepiece was “pinched optics” so I’ve obviously read enough that something triggered in my brain. 

Got some more practise at collimating the secondary too. I think I’ve got a better understanding of that now too. 

Thanks again for everyone’s help. It took a lot of stress and worry out of the situation. Dew heaters on. Scope cooling again. Time to wrap up and get out there!

Clear skies!

[Littleguy80]

Officially back in business. Great couple of hours. Comet 38P, NGC 2392 (Eskimo Nebula), NGC2301 (Hagred’s   Dragon) and NGC2169 (37 cluster). NGC2158 next to M35 is neat. I thought it was a Nebula at first look. Got the E star in the trapezium. First look at M78 of the year. M81/M82 looking lovely now they’re a bit higher in the sky. M82 close up was particularly good. Few other classics like the Beehive and M67. Feeling quite relieved after the earlier issues.

[steppenwolf]

Great news, well done!