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Welcome to IIS
Quick Answers
1. No difference visually as both telescopes have similar aperture and focal length. I think from memory the 8” Dob has an f6 focal ratio thus slightly narrower FOV than the f5 OTA
For visual astronomy as a beginner , the Dob is probably the better choice as it’s primarily designed for observing and easier to set up. A drum stool is a handy accessory to use with the Dob as you can adjust your sitting height to suit the position of the eye piece. The f5 OTA requires a mount ( EQ or AZ ) , hand operated ( manual ) or a Goto ( automatic) with telescope control.
2. For visual observing, steer away from f4 Newtonians , they are designed for imaging with their fast optics, and are more difficult to collimate. They are an advanced Newtonian and obviously more expensive.
They “can” be used for visual observing with an appropriate coma corrector but why use an imaging Newtonian as a visual telescope , doesn’t make sense unless you want to venture into imaging later on.
Cheers
Martin
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