Need some focusing tips

[traveller]

Hope to hear some focusing tips from more experienced members.
Currently, I use the frame and focus function in Backyard EOS with DSLR and ED80. On a "good" night, I can get FWHM around 3.5 (been using Antare as the focusing star).
But most of the time, I get around 4.
I am imaging from 10km of Melbourne CBD so guess LP is a factor.
I also use a fairly old R&P single speed focuser on my ED80 (I replaced the original single speed crayford).
Should I clean and regrease the focuser (stay with R&P or back to crayford?)
What other tips would you recommend? (moving to a dark site 3 hours away is not an option :))
Bo

[multiweb]

In the past I have used a longer dovetail and braced the focuser tube into an extra ring to hold it. That helped with sagging a bit but you still need a solid focuser so it doesn't slip. I used a bathinov and refocused often at the beginning of the night but as it goes on it doesn't change as much. Few rags on the scope also help with dew and keeping the tube temperature closer to ambient. In bad seeing it's very hard to focus accurately though. Not much you can do then.

[traveller]

Thanks Marc,
I will try both the Bathinov mask and BYE FWHM method and see what happens.
Seeing was a problem, esp on Monday night.
Bo

[multiweb]

Mate there's nothing you can do in poor seeing unfortunately. Even with a bathinov it's hard to nail it. Harder by the numbers because it just jumps all over the place.

[rustigsmed]

hey Bo,

I had fat stars on Monday night .... they were a lot tighter on sunday night ... will have to ditch my data for one of my objects unfortunately ... I thought it may have been from fiddling with the OAG after focusing but i'm not so sure, thinking the conditions.

Cheers,

Rusty

[traveller]

Think you are right Rusty,
Sunday was a lot drier than Monday (not sure what the air moisture was, maybe time to invest in an el cheapo weather station).
Last night was a total write off, as will be the next 5-7 days. :mad2:
Bo

[cfranks]

It could be that Antares, being embedded somewhat in nebulosity, presents a fairly fat star to Backyard EOS which might confuse the resultant focus point? Try another, dimmer star if possible.

Charles

[Geoff45]

FWIW light pollution won't affect focus, so moving to a dark sky won't help.
Geoff