Ad Astra Observatory

Art Morton wrote:
> On Jan 28, 2009, at 9:38 AM, Jimbo S. Harris wrote:
>> Do you know if the focus shifts “in” or “out” during the course of

>> the night?
> Yes. as it get colder, out and warmer in.
Dude, you are a font of knowledge. Thank you.
>> Do you know how much it shifts by?
>
> Colder, two tick max. Warm on tick max.
2 *ticks*? This is like a couple thousandths of an inch?

> Totally predictable and easy to compensate for.
>
> The strange thing is that all the colors seem to be the same. There
> is not focal differential for the colors at any temperature given the
> filters I use.
I would not have been surprised to hear that it was either way. Are your
filters parfocal, or do you have to refocus between them?

J