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Does focal extenders need a ridiculously long back focus?
Hi all, I'm a long time owner, first time user of the explorer scientific focal extenders (2x and 3x). Last night, as I prepare for the Jupiter opposition, I find I needed a 20-30cm backfocus to reach focus when I attach my 2x extender, and extension tubes ran out for the 3x.
For anyone that has used it, is this normal? If not, what could I be doing wrong? My imaging train consisted of: ASI1600MM > Filter wheel > Nose piece > 2x extender > loads of extension rings > focuser > more extension rings > GSO RC8.
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