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David if your scope has a focal length of around 1000 mm and an aperture of 5" (127 mm) then the focal ratio is 1000/127 or around f8. A 5" f12 would have a focal length of around 1500 mm (5" x 12 = 60").
I've thought about a folded refractor myself. For a long scope like a 5" or 6" f15 it can make the telescope a lot more convenient and easier to transport.
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