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Will a 2x barlow improve guiding with this setup?


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I've recently acquired a 70/700 frac from Luke (Beamer3.6m) at a great price :) . Anyways, im looking to use it as a guide scope, however my imaging scope will be my 250px which is 1200mm focal length. With this in mind, im wondering if the guidescope will struggle accuracy wise considering it is a shorter focal length than the imaging scope?

Thinking aloud while typing I just realised that the guide cam (ToUcam) has a much higher magnification than the imaging camera (DSLR) so its probably swings and roundabouts.

Anyway, I'll still ask the question... would a 2x barlow on the guide scope improve accuracy by effectively cranking the focal length up to 1400mm?



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No need to add a Barlow! It's all about seeing conditions and image size in pixels. Most guiding software (eg PHD ) can guide at sub-pixel accuracy so there's no need to go for the longer fl guide scopes.

Infact some are using reducers to give a wider field to find suitable guide stars!

I can guide ( sometimes!) my 12" LX200 ( 3000mm fl) and hold a star on the 20 micron slit of a spectroscope using a ST80 ( 500mm fl) QHY5 and AstroArt V4

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Wow..thanks Merlin, thats what I wanted to hear. I should have more faith in the guiding software, that PHD is made of good stuff. Its a shame the 70/700 doesn't have a 2" focuser on it, otherwise I could swap scope roles and get some better widefields as well.

Hoping to order a 2nd dovetail bar and guide rings very soon, then I will have totally gone over to the Dark Side proper :)


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