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Guide scopes are really a relic of the Cold War or was it the Paleozoic era?
Serioiusly though OAGs are totally the way to go or self guiding in front fo the filters. Guide scopes work at shorter focal lengths OK but at long focal lengths its a no -go.
Having said that I use a little compact, weighs nothing, Vixen VMC 95mm scope as a guide scope on my CDK17 scope when I use the reducer. That's only because the reducer has no backfocus and only an STL11 would fit. I have to reduce exposure lengths to avoid eggy stars but I can do 5-10,minutes ok.
At long focal length a guide star on something like a MMOAG can occasionally be a bit of a bother and you end up imaging the object away from the centre of the sensor but that is rarish. With an STi guide camera (I have 2 now) I find a guide star 90% of the time close by with no special handling and the rest of the time it simply means looking a bit to the left, right up or down a tad to find one.
At shorter focal lengths the OAG usually has a choice of guide stars.
An OAG is still not a perfect solution as it adds weight, are hard to focus, can flex themselves or get in the road of other components but they are one of the best solutions currently.
Greg.
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