If I'm reading this correctly filters are better suited for faster scopes with larger EPs? I've been considering either an UHC or LP. I know some are one in the same but it seems more reasonable to me to find out if my scopes would benefit from a filter. Do any of the LP or UHC or OIII filters work for visual?
Uh, no, they aren't only for fast scopes and large eyepieces.
They work by restricting the bandwidth transmitted to mostly the nebula emission lines and blocking the rest.
This increases contrast, making the nebulae more visible.
They work for all f/ratios.
However, as the field dims with increased magnification, the contrast enhancement diminishes, so they are typically used at low powers, under, say, 10x/inch of aperture.
Yes, your scopes would benefit from the use of nebula filters.
Just about all of them were originally intended for visual use.
There are a few basic visual types:
--broadband (aka LPR). Transmit all the light except for a swath in the yellow-orange. These were designed back when those wavelengths were where most light pollution was.
Today's light pollution spans nearly the entire spectrum, so the effectiveness of these filters, which is modest at best, is better at sites with already dark skies.
--narrowband (aka UHC). Good visual ones transmit the 486.1nm line of H-ß, the 495.9nm line of O-III and the main O-III line at 500.7nm and almost nothing else.
Bandwidths of 21-26nm are best, with transmission at all 3 lines over 90%. Wider filters yield less contrast enhancement.
These work well on all forms of emission nebulae, so this is the 'universal' nebulae filter.
--line filters (aka O-III or H-ß). For O-III only filters, a 11-15nm bandwidth with both O-III lines >90% transmission is best. For H-ß filters only, a 9-12nm bandwidth with transmission of >90%.
O-III filters work best on planetary nebulae, supernova remnants, and Wolf-Rayet excitation nebulae. H-ß filters work best on large faint (because you need maximum contrast) hydrogen emission nebulae.
Line filters yield the maximum contrast for the types of objects viewed.
Photographic O-III filters are narrower, and only pick up the 500.7nm spectral line. This yields more contrast, but requires longer exposure. Not best for visual.
Photographic H-ß filters don't exist. All hydrogen nebulae emit more energy at H-α in the deep red, but because we don't see that wavelength much at night, we use the H-ß in the blue. Imagers all use H-α.
Photographic Narrowband filters don't exist because imagers prefer to expose specific wavelengths and combine images. A UHC-type would yield too little contrast, and they don't want the H-ß anyway.
Photographic use of broadband filters is possible, but the effectiveness of the filters has diminished, so this is becoming far less popular.
Edited by Starman1, 09 February 2019 - 04:57 PM.