Thanks guys,
At the moment my polar alignment is surprisingly good (I am in the Southern Hemisphere which makes things trickier), but I’ve had excellent results using ASPA. It will be interesting to see, once I get my autoguiding set up, if drift align through PHD2 is any better.
I’ll probably go with OAG as I’ve got enough spacers of different sizes to get the appropriate backfocus. I guess that leaves me with the question of which camera should I buy. I understand the 120 has a smaller sensor than the 290, but that the 120 has larger pixels and is therefore more “sensitive” to light. ZWO gives a figure of “30% better tracking” accuracy on the 290 compared to the 120 as well. OAG on my slow telescope would mean that not much light is going to the guide camera sensor, so I need a more sensitive sensor, which points towards using the 120. On the other hand, the higher focal length means I need better tracking accuracy, pointing towards the 290. I’m not prepared to spend more than the price of the 290 (I’m also saving for a dedicated AP camera), so how should I negotiate this trade off?