pbsastro wrote:Now I would welcome opinions about what is best for visual. Na or HeD3. I will go only with one of those. Na and HeD3 are so close, only 2nm (20A) apart (587.5 and 589.5) that we could think it could be possible that just one filter could reach both with extra tuning, but I think the blockers would need to be different.
From the sample I see Na and He are similar, mixing WL view with plages and faculae. My thing is that I love CaK views, but I am reducing it to near zero, due to possible eye damage, so I am considering that Na could give me the same faculae and plages in a WL background. It may may not look so good as in CaK, but the Na light is much more visible to the eye, so that could be an advantage for visual. And it would give two in one (WL and CaK). But I guess if it were good enough it would be more used.
Looking at some graphics, the HeD3 line seems to be too weak relative to close neighbor lines, so I fear it may require some image processing and be not so adequate for visual.
Another issue is that both Na and He lines are narrow, below 0.4A, so that Mark suggests double stack may work better, so it will not be no easy to get equivalent samples to help decision.
Pedro
If I will be you, I'd never spend money for any of these yellow filters. Too insignificant difference vs, for example, green light.
May be G line at near 430nm? At least much higher granulation contrast.
I may be well wrong in my reasoning, but I really never saw any impressive image of the sun through these yellow filters.
Valery.