John in Penzance

Thank you all. Stuart may have cleared up why both filters exist for visual observation: increased retinal sensitivity to green light compared to red sounds like a reason for using a Hβ filter. Adrian notes that the intensity ratio of the two frequencies shows where is hotter or cooler. For imaging, if each filter feeds a false-colour into a merged image, perhaps any resulting colour variation would show temperature gradients within a gas cloud?

Any bit of Hydrogen will be spitting out both alpha and beta frequency photons so I'd have thought either narrowband filter will show the same image. Obviously I'm mistaken since both filters are available, but Google as I might I've failed to find out what difference there is between the image each produces or why the images differ. There will be a simple answer?