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Hi Jeff
I concur with Phil. I have a 7" F12 'scope and I add a reducer/corrector which brings the f-ratio down to around F9.6, which is still classed as slow. Several IIS'ers image at between F6 and F8, which gives a nice, wide field of view, matches the characteristics of the ccd sensor and is less demanding on the mount in terms of auto guiding.
You generally only use a Barlow if you are taking high resolution, short duration exposures of the Moon and the brighter Planets.
Cheers
Dennis
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