Posted by David Mottershead at 19:34 on 2010 Oct 17
HelloWhen using my 120mm refractor (see here, http://britastro.org/baa/index.php?option=com_kunena&Itemid=100007&func=view&catid=18&id=195#201), and depending on what I am viewing and the magnification I am using, I stack Baader Neodymium and Fringe Killer filters, giving the same results as the Baader Semi APO filter. The advantage of having the two (I already had a Neodymium filter, so simply added the Fringe Killer) is that I can still use them individually, e.g. the Neodymium to reduce light pollution etc, but then gain the benefits of the equivalent of the Semi APO filter when stacked – and the Semi APO is apparently well regarded as a planetary filter when used in achromatic refractors.As for the 150 refractor, that will give more light grasp than the 120, allowing finer detail to be seen, and will allow a higher theoretical magnification, but in reality I’d suggest that the highest magnification that you might use on the 150 will be pretty well the same as that of the 120 – and magnification isn’t what it’s about anyway. The better light grasp on the other hand is always worth while to catch the finer, more subtle detail that a smaller scope can’t resolve. If your main interest and area of observation is lunar and planetary, have you considered a Maksutov? These are, in my opinion, one the best lunar/planetary scopes around.A good image of Jupiter as well, and nothing wrong with black and white.Hope this is of some use.