The Lumicon oxygen III filter shows slight
performance
change from F/4 to collimated light. I doubt you could observe the
difference
visually, unless the observing conditions were juuuust right. Please do
not jump to the conclusion that this filter is useless at F/10 or
longer!
This filter, and the H-Beta, have a long history of successful
application
in long-focus scopes, such as the ubiquitous Schmidt Cassegrain.
The peak transmission is a little lower than
advertised.
I suspect my background measurement was a little off. I'll try to get
this
resolved soon.
