We regularly use achromat doublets in our spectroscopes - the focus difference between CaK (in the blue/uv) and the green (OIII) can be up to 2mm.
I would not think that the thickness of the filters would compensate for this difference.
I think one can look at what is happening this way..
The colours are focusing at different points it would seem very necessary to re focus so the point of focus is is say the blue range.
I really dont know but I would try re focus regularly anyways irrespective of filter change..I would probably check focus many times with one filter...
alex
If get a mono camera I intend to try my 150 mm refractor, an old double, with various filters and see if it can be used. It seems sharp but in the past very blue images via dslr but I often wonder that as you are working one one colour at a time it could work.
alex
I will give it a try and see, i just had some problems with my orders, once i sort that out then i will confirm, still waiting an answer from a seller about something then i will definitely order the filter wheel and LRGB filters.
