Any tips for focusing with a UHC filter

[Warped Drive]

After an eternity  I managed to get a couple of nights observing in. I bought a Skywatcher UHC filter back in the Spring and have only gotten to use it a couple of times. It certainly made a huge difference, several objects  I could not see before or were just very dim fuzzy patches came to life.

Last night I was looking at M27 The Dumbbell and was amazed at how big and bright it was but it was very hard to tell if it was in focus or not, I kept having to slew to a bright-ish star near by to focus on that and then slew back again. M57 The Ring is not so bad as there are one or two small stars in the FOV to reference off. Is that what you would expect with a UCH filter. Even though I bought it as the Skywatcher brand it came in the same box and packaging as a cheap Moon / Sky glow filter I bought on ebay.

[PHIL53]

That is exactly what I do to focus with any of my filters (OIII and UHC): focus on any of the little green (when using the OIII) stars available around the target !