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Yes, the SCT has nearly 3 times the effective focal length of the refractor so the field will be 1/3 the size. Given that the DSI II has a fairly small chip, you really want to pair it with a short focal length scope if you want to encompass a reasonable field. So of the three, the ED127 is definitely the easiest (ED 80 better still). If you're beginning in astrophotography you definitely don't want to start with long focal lengths. They make extreme demands on the solidity of your mount, length of exposures, guiding tolerances etc.
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