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Gene,

Thanks for sharing your experiences with Baader. What impressed most about Baader was the baseline as seen in my post above. I looked at the German report also and saw that my results were in line with what they reported. For that matter, even the Televue peak near 700nm and red noise in Lumicon/spectral shapes are similar to what I obtained in my experiments.

I am not sure if the Baader spectral shift would be a whopping 32A (3.2nm for metric lovers) in real world. Even with the lower transmission, Baader OIII should be an excellent AP filter because of the clean baseline, could anybody else weigh in?

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I've been evaluating filters from Lumicon, TeleVue and Baader in the field for the last few months.

Though I generally agree with David's conclusion regarding bandwidth and effectiveness in contrast enhancement, I am not so tied to having my filter be the optimum filter for the lines observed.

I'll explain.

On a lot of objects, my 12.5", in dark skies, has an adequate light grasp that the nebula is quite visible without a filter. Adding a filter increases the contrast, allows me to see details in the nebula, and makes the view that much more profound.

But, the narrower the bandwidth of the filter, the darker the overall field is.
Stars get dimmer or disappear, and while the nebula is definitely improved, the esthetic view is somewhat diminished. After all, in a photo, you get the nebula AND the stars.

And, though I certainly agree that the most aggressive filter usually produces the best view of the nebula, it doesn't always produce the best view.

For instance, though the Lumicon UHC filter definitely revealed some fainter structures in the Orion Nebula, the much wider Baader UHC-S (almost a broadband, it's so wide) revealed a more esthetic view of the overall scene, and allowed a lot more reds to be viewed in the nebula (not surprising, given the strong red transmission of the UHC-S). In this case, the view with no filter was magnificent, but the UHC-S gave a prettier overall scene.

On NGC2359, Thor's Helmet, the Baader O-III gave a much darker image than the Lumicon O-III, but with similar nebula enhancement, while the TeleVue O-III did not provide quite as much nebular enhancement but still gave the "brightest and prettiest field" of the 3.
And, the nebula was definitely strongly enhanced over the no-filter view.

One can argue the purpose of a nebula filter is to view the nebula, and that one which produces the best results is the best filter. But I, and probably others, enjoy the overall view when viewing an object. I even enjoy the field of NGC2359 with no filter at all. And the TeleVue O-III yields an image that is definitely enhanced and which is also a very pretty field. In already dark skies, my wife even prefers a broadband filter for most bright nebulae because she wants to see a lot of stars in the image with the nebula.

I could probably get the same view with a Lumicon UHC filter, if I read David's argument right, and use an O-III filter when I need more enhancement on a particular nebula, at the O-III lines part of the spectrum. Instead of a wider O-III filter.

I don't disagree with that, but I also find there are circumstances where the maximum enhancement isn't necessary. I have had a lot of people have a hard time holding their heads in the right place to see an image through a filtered eyepiece because the view was dark, and though the nebula was less enhanced, a wider filter was easier to use for everyone sitting down at my scope.

I see both points of view.

Of course, if the nebula is faint, and I'm looking for details in the nebula, the narrower bandwidth (that doesn't exclude the line or lines) is the one I grab. And it would likely be the one I recommend unless some other factor overrides that.......like seeing reds in M42, for example.

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