What's trick to focus on 12inch Dob?

[wine52]

Some time ago I managed to see Saturn clearly, but of course forgot to write down the Barlow/eyepiece configuration. A year later, I tried again and just could not get good focus with any eyepiece. The focusing tube is either too short/not long enough. The mirrors are clean and perfectly collimated. Must be something simple!

[raymo]

If it is a Skywatcher/Saxon dob maybe you have fallen into the trap of using the black 2"eyepiece adaptor. It's got a bevel at one end, and two
chromed knobs on the side at the other end. These hold a 2" eyepiece in place. Put it away in it's box. The flat plate that carries the tube you slide the 1.25" eyepiece into fits directly into the focuser.
raymo

[Chif]

Yep, what Raymo said. If that doesn't make sense, upload a picture of your setup and we can point it out.

Welcome to the forums by the way.

[wine52]

I knew it would be easy! Many thanks