Unable to focus when cold

[steve000]

Morning all, I write this as I'm in a tent at 5:38am freezing my peripherals off after hosting an astro camp for work mates. All was going well until I tried to show everyone neptune. At 32mm it was in focus under 15mm totally blurry no matter how hard I tried to focus. I'm using my 12" Newtonian. last year I had the same prob on my 6" Newtonian. Collimation was checked and ok at the start of the night. I figure as the mirror drops from 20 odd digs to 5degs it changes shape and throws collimation out. correct? I will check it at sunrise but that's my theory. I'd love it if people had opinions on this and possible fixes. Thanks again :)

[Alchemy]

Not really sure of your issue as focus will only shift a mm or so. I had a 12 inch newt for planetary imaging and the shift while noticeable on the screen was not a lot over the cooling period.

Stating the obvious... Was the eyepiece fogged on the inside??

[el_draco]

hypothermia :rofl:

[steve000]

ha hypothermia..

and nah i dont think it was fogged, it could have been but i dont know.. next time though I will look out for that and see, perhaps they were.

the 32mm was in my pocket... 6mm was not

[astronut]

Was the focuser still operating at full range?

[steve000]

yea all was working fine. I think it must have been fogged on the inside.. next time I will take note and report back.

Thanks all