Quote:At a quick glance, they might be considered close to a 'Broadband' type of light pollution filter - As opposed to say, a UHC-type (for example). I suppose the only popular filters that they could be compared to, would be the 'Deep Sky' types. However the GCE's actually do improve the view on galaxies in my heavily light polluted backyard. And, I’ve never heard or read about any skyglow-type, or other LPR filters being able to accomplish this.
Quote:Al Milano wrote:Quote:At a quick glance, they might be considered close to a 'Broadband' type of light pollution filter - As opposed to say, a UHC-type (for example). I suppose the only popular filters that they could be compared to, would be the 'Deep Sky' types. However the GCE's actually do improve the view on galaxies in my heavily light polluted backyard. And, I’ve never heard or read about any skyglow-type, or other LPR filters being able to accomplish this.Then perhaps the author hasn't heard or read nearly enough about these filters. It has been commonly known since the late 1980's that the broad-band "LPR" filters like the Lumicon Deep-sky can indeed help the view of galaxies to some small degree. Usually they end up notching out the common emission lines of mercury and sodium vapor while passing as much of the rest of the visual spectrum as possible. This can sometimes result in a small but definite increase in the contrast for some of the larger and more diffuse galaxies like the ones the author looked at. The improvement tends to be greater under darker skies than under conditions where the skyglow is more notable. Indeed, the DGM Optics GCE filter was rigorously tested and reviewed way back in 2007: CN REPORTS: DGM Optics GCE Filter While some benefit on some galaxies was noted in that test, it was also noted the improvement was mild and was not universal. Indeed, the GCE filter tended to be a bit less effective under some mild to moderate skyglow than the Lumicon Deep-sky filter was. In fact, under moderate to severe skyglow, the broadband LPR filters tend to lose what effectiveness they have as the skyglow overwhelms the faint detail in galaxies even when filtered. I am glad the author had some success with the GCE filter, as it does help sometimes. However, while it works to some mild degree in some circumstances, for those expecting a lot, they may be disappointed. The GCE doesn't provide nearly the same level of enhancement on galaxies that the narrow-band and line filters do on emission nebulae. In short, they won't work miracles, so don't expect too much. To get the most out of galaxies, the "gasoline" filter is still probably the best bet. Clear skies to you.
Quote:One thing that may have made a point of difference in the author's experience (other than a lack of alternative filters that is...) is that he was using them with binoculars - the 10x50s being the most common for him.So with that in mind, a slight drop in background brightness may have greatly improved the constrast for number of objects. I know my ~30nm O3 filter approximately "draws even" on stars under my highly light polluted sky. I would likely get better performance with the GCE on clusters while most nebulae wouldn't get quite the contrast boost I already gain from the O3.Cheers,Cam
17.5" f4.1 Manual Discovery Split Tube Dobsonian (Love 100 AFOV and wide TFOVs).
Denk II Dual Power Switch 3x3=9 powers x3 OCS = 27 power options per eyepiece pair.
2.3x40 to 25x100 Binos (and many in between).
Quote:The plot is quite a bit different with lots more transmission for the GCE.
Quote:One distinction I would note between the GCE vs a traditional Wideband (Deep Sky type) filter is that they all use a wideband design which are typically just a 50-55 nnm wide bandpass, where as the GCE is a true notch by design. Some WBs are a blocked in the red others have high TX% at 656.3. While I didn`t have a Deep Sky when I designed the GCE I did have a prototype which I used as an A/B and found the GCE to be a bit brighter than my prototype WB.