HOMEMADE FOCAL REDUCER: above - December 2007 Comet Holmes expanded beyond the fov of the ETX-70 and Starlight Xpress MX916 CCD. A focal reducer was devised and finalised on a spare coated 20mm diameter achromat of 120mm fl in the tube coupling scope and CCD with a power x0.7 to nearly double the gross sky fov from 90' x 60' to nearly 120' x 90' coverage with excellent stars images even to the corners.
PIGGYBACK ETX OTA UPDATE: serves 1]70mm aperture angled-finder for my 30cm LX200; 2]small astrograph for DSLR via rear port; 3]CCD astrograph camera via flip-mirror port. Laptop planetarium for ETX control. Ring + rail set for ETX-70
ETX-70 STRIPDOWN+MOUNTS: disassembly of the OTA of OG and tailpiece [via 6 screws] exposing flip mirror and the drive system of the ETX and mounts both altaz and polar and my flexible focusing knob.
The effectiveness of the DSO imaging [when
exceptionally stretched due to the
modest 70mm aperture and relatively short exposures] is probably due to
good 'flat' and 'dark' frames applied to the 'light' frames - I've used
a translucent icecream tub at dusk for the former to good effect.
The exposed OG is very prone to dewing - resolved with a zero cost long
dewshield made of black card which is probably twice as long as the
official Meade screw-on hood.
PIGGYBACK CAMERA: The ETX can image OK in altaz mode but at longer focal length, like the native 350mm fl f/5 OG, field rotation is obvious. However a piggybacked camera with short focal length for widefield works in brief exposures works - if the camera is effectively counterbalanced - here via a pipe-clip and weight from my LX200.
text & images copyright Maurice Gavin - May 2007