I have just ordered a broadband (45 nm) hydrogen alpha filter from Ian King Imaging. The Hyperstar III lens assembly works at f#2 which means a steep cone angle for the incoming rays of light. Unfortunately, the makers of narrowband filters design their multilayer dielectric stacks on the basis that light enters the filter at normal incidence – problem!! The Hyperstar III therefore “sees” a narrowband filter operating at a pass wavelength outside the natural linewidth of H-alpha radiation – in other words it doesn’t work!! I will see if a broader passband on the filter allows the Hyperstar III to see good transmission at the H-alpha emission wavelength – and my first target will be CTB1 – the supernova remnant in Cassiopeia which up until now has been a dismal failure for me (but not for Steve Cannistra who has a beautiful image of this one on his web site).
|
Leave a Reply
|
|
Entries (RSS)