[graham.hobart (Graham stevens)]

Having issues with getting distance right with FLI +FW+OAG with coma corrector and also have a small SV 60 which has a native flattener which needs the same back focus (55mm).
Are there any flatteners/ refractors which have longer back focus (apart from hideously expensive ones?) . Something around 300-600mmfl . Maybe a frac+ flattener combo which allows for CCD +FW +OAG or a corrected flattened frac which doesn't need an additional flattener?
pipe dream?
cheers.
Graham