I tested the Celestron branded version of the Baader UHC-s filter alongside an Optolong UHC, Lumicon UHC, Starguy UHC, DGM NPB and Thousand Oaks LP-2 (UHC-type) several years ago with Dobs from 5 to 16" both here under the Dallas light dome in a white zone and from the club dark site in SE Oklahoma.
It was around this time of year as I remember having the summer Milky Way nebulae available for the tests. It took several months to get a good run at all of them from both sites in all the gear.
The BaaderUHC-S/Celestron UHC-LPR, Optolong and Starguy are wideband filters. The Lumicon and DGM are narrowband. The TO is a bit less narrow than those two but a narrowband.
The goal was to increase the apparent contrast of the available large emission nebulae when visually observed and the results were plain and easily described. The narrowband filters were effective from both locations in all 3 scopes at every exit pupil used. The wideband filters varied some little bit between sites and less between scopes and they were easily seen to be ineffective compared to the others.
So I gave the Optolong to a club member that was interested in it despite my analysis and tried to sell the Celestron/Baader and the Starguy. When they wouldn't bring $25 each, I put them in storage. As I recall I gave BillP the Starguy and threw the Celestron in the trash a few years later. The TO may still be in a drawer somewhere in the back bedroom/office. I carry the Lumicon and DGM in my case when I observe, using the Lumicon > 95% of the time. The DGM is quirky as it renders very red stars I find distracting but it is useful as it passes the H-Beta line at a higher rate.
The H-Alpha line is not visible to the eye but is captured effectively by AP.
"As for the "night" H-alpha filters, as mentioned before, they are primarily used for imaging. However, the
reason they are not suitable for visual use is mainly because the human eye has very low sensitivity to dim H-alpha light. These filters usually have transmission levels at H-alpha that can be quite high (often exceeding 90%), but the eye just can't respond well to dim nebular light at that deep red H-alpha wavelength. In very large apertures, one may use an H-alpha imaging filter to see red in some of the brighter emission nebulae like M42 or M8, but the overall view is generally notably inferior to that seen with the narrow-band and OIII line nebula filters. Clear skies to you." - David Knisely 3/28/13; posted to forum string WHEN DO YOU USE AN H-ALPHA FILTER?
"Nothing is best viewed at h-alpha wavelengths. Our eyes are so insensitive to light at 686nm that we can barely see it." - Don Pensack 7/27/13; posted to forum string H-ALPHA OBJECTS?
For my visual use wideband nebula filters have no value. Generally respected experienced observers point out some niche usefulness but I am very well served by my narrowband kit for all applications and much better served to my eye than by widebands according to my experience.
An observer inexperienced with nebular filters is poorly served IMO by a recommendation they use a wideband filter to try and increase the apparent contrast of nebular objects they may try to observe.
Edited by havasman, 19 July 2019 - 02:53 AM.