Hi,
Recently I made my take on the standard '4 or 5 position manual
filter wheel'.
It works well, it's lightweight and it's as thin as I can feasibly get
it.
However, without doing a lot of homework on the actual typical
order and placement of the typical imaging filter arrangement, I went
with just what I thought should work.
In short, I have a rotating 4 way platter with Red, Green and Blue
1.25inch filters screwed into it.
(the 4th spot is empty, creating the 'straight through' aperture I need
for imaging luminance with my Mono DSI camera.
I have the Meade nosepeiece mounted at the front of the filterwheel
and the Baader IR filter screwed in there.
So for a typical image I always have the IR in place and select
NONE(straight through), Red(with IR), Green(with IR) or Blue(with IR).
I hope I'm being clear here, I'm probably over-describing what's obvious
to everyone...a look at the pics might just make it clear where the
filters sit.
http://mywebsite.bigpond.com/astrost...ter_wheel.html
I assume this is a typical situation for filters.
My question....(finally!), is this:
When I image straight through (IR in nosepiece only) the focuser needs
to be at focus point A.
However when I do RGB (again with IR nosepiece in place) the focuser
needs to be at focus point B. (all colours, this spot is the same).
What is causing the focus point to shift? Is the Baader IR adding a slight
Focal reduction to the optical train and should it be closer physically
to the face of the colour filter?
I would like to have a situation where refocusing is not necessary or
at best minimal for all 4 shots (L,R,G,B)
Is this asking too much, or a typical situation?
Thanks in advance,
Steve B.