Filters for fun science

[Marko]

I have of late become more interested in use of filters to optimize or modify the views of nebula.

One thing I am evaluating is to see if I can find a slightly better filter than the Omega NPB which I stand by as my all time favorite filter in the field. I believe I like the NPB so much because it also lets in a lot of H-Beta and even H-Alpha which our eyes are week on but nebula can be very strong in H-Alpha. Where there is strong H-Alpha there is generally H-Beta that is 1/4 or so of the intensity and that wavelength our eyes will respond well to with scotopic vision (rods).

I picked up a Baader UHC-S to do shootout with the NPB because they both allow H-Beta near the O lines with very high transmission. My first tests with these were last week and I hope to mess with this more this weekend. On the 'mexico' part of NA Nebula I felt the Baader offered a better view was my initial impression. The NA Nebula is very strong in H-Alpha/H-Beta and O3 as you know. I will be looking at these much more this summer on the great southern nebula as well as Veil and NA and Dumbell.

Another 'science experiment' is that I picked up a Sloan 'r filter which is a sharp skirt bandpass from 555-695nm. This filter I picked up as a sort of 'nebula killer' filter. The idea was to expose faint stars that are buried in hot nebula regions or to better see the star cluster members more or less by themselves. This is a fun filter. It nukes M27 entirely due to PNs are mostly O3. Very late I got to M8 and was noting it did not kill all of M8. I suspect that in very hot areas of M8 that the filter does leak a very small amount of the very hot green to blue emission and that combined with 'maybe' the very hot H-Alpha being so hot that my very weak scotopic response was able to see just a little bit of that as well.

I would be curious if others have actually tried to decide if they were every able to actually see ANY H-Alpha on very hot nebula and if so what filter was used? Everyone tells me we humans cannot see any H-Alpha but I just don't know and wish to evaluate. My next experiments will include M8 and specifically doing some filter stacking as well as use of narrowband H-Alpha filter. Just curious.

Marko

[Marko]

Last new moon Jupiter was finally getting to a respectable height for decent viewing so being the end of a 3-day star party with the seeing being amazing I studied Jupiter for a while using my newly acquired TMB eyepieces at high magnification.

What I picked up a couple years back is that the NPB filter brings out the rings is stark contrast and this was no exception. The NPB passes a few wavelengths and so rather than monotone you have a bi-tone image and the rings really come out very dark. It was quite a view to be sure in the 18". The NPB is of course a nebula filter but on Jupiter it has the dual purpose of knocking down the intensity to a respectable level as well as offering an extreme contrast boost for the bands.