Filter incoming Hb

[jetstream]

I'm not a beginner but feel like one everytime I try the Eridanus Loop... it might benefit some newcomers to hear about small aperture (and large ones) with respect to filters.

It is a myth that tight OIII and Hb filters wont work well in small apertures. Period. I use them all the time in 90mm,120mm and 130mm scopes with great luck. The 90mm frac shows the California nebula and Barnards loop well in Hb- if- the exit pupil is large enough, in this case the 42mm LVW fits the bill. This applies to any aperture IMHO. The Veil and others show well in the 90mm/OIII etc.

So, my latest attempt at the Eridanus Loop in the 24" f4.1 will now include a Baader CMOS 5.5nm Hb, much tighter than my 12nm(?) Astronomik Hb and hopefully with high transmission.

I cant say is this filter will work in small apertures yet- it should but we'll see. I am fortunate to find one and it should be here next week. After years of trying this object maybe this filter will confirm suspicions of seeing it.

The main things with filters are to get high transmission and tight bandwidth IMHO and a couple of brands seems to give this.

Mods please move if this is in wrong section, but I do feel like a beginner when the scope is pointed at this objects area.

Gerry

[Littleguy80]

Excellent post, Gerry. It’s an area I think most astronomers wrestle with at all experience levels. What’s your experience with exit pupil size and something like an Hb filter? With my 10” dob I’ve gone over 8mm exit pupil with an Hb on Barnard’s loop and California Nebula and to my eye it works well. Does the principle of not going about 7mm exit pupil stop applying with narrowband filters? 

[jetstream]

1 hour ago, Littleguy80 said:

What’s your experience with exit pupil size and something like an Hb filter

 

1 hour ago, Littleguy80 said:

Does the principle of not going about 7mm exit pupil stop applying with narrowband filters? 

Great questions Neil, contrary to many beliefs using very large exit pupils can work eventhough the actual light disk (and other things) are self regulated by the eyes when doing this. Its best to try everything- I do... including using the 42mm in my f4.8/f4.1... with and without the PCII.

For sure try above 7mm... even if the sec shadow shows.

For me, a 6.5mm exit pupil or thereabouts is nice with an Hb, but 5mm works too. The other night the 32mm TV plossl outdid the 24mm because of the increased light disk size IMHO.

This new 5.5nm will probably want 6mm+, just guessing. My motto- try everything! lol!