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Originally Posted by matt
Thanks Rob. Funny you should mention the issue of focus. I was thinking exactly the same. I was noticing the other night that these SCTs present a couple of probs in this dept. I was familiar with the obvious image shift as you rack the focus in and out, and also the not-so precise nature of using the focuser knob. However, I've also discovered another issue which makes focusing even harder using the standard knob. The simple act of applying inward or outward pressure by your hand on the focusing knob, pressuring the focus mechanism in a lateral direction - towards or away from the corrector - also impacts significantly. I've noticed some quite considerable loss of focus the moment I take my hand away from rotating the focus knob precisely when the image is crisp and sharp on the screen. Honestly, it's a nightmare!!!!! Does this problem have an astro/techo name i'm unaware of?
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Matt, not sure if this has a name, but I'm not surprised by this action given the mechanics of mirror shift focussers. Perhaps Dennis can shed some light. He mentioned something about a mirror lock that he has for his C9.25? I tend to approach focus with an anti-clockwise turn and then do the fine focussing with the motor focus unit. Re focussing every now and then in the hope I'll jag perfect focus for some of the avis.