Quote:
Originally Posted by OICURMT
You are missing the point. There does not exist any single filter that can give you the 0.1nm resolution required to view the specific Hydrogen Alpha wavelength.
The etalons previously described uses two plates that reflect the light back and forth within a narrow gap, which when tuned to a resonant frequency, allows light of a specific wavelength (with a narrow band) through. Any wavelength outside the tuned interval is "rejected".
Wikipedia have an excellent article on the subject -> http://en.wikipedia.org/wiki/Fabry%E...interferometer
Note that this relates to the etalon only. You will also need a blocking filter, which takes everything outside the Ha band and blocks it, allowing viewing of only the desired wavelength. Note that the blocking filter also screens out potential harmful wavelengths that still pass through the etalon (think harmonics).
OIC! |
Tks - finally - you said the magic word that didn't jump out at me earlier - Etalon. Like most people I have had particular preconceptions about what a narrow band pass filter is - a circular piece of glass with high tech coating rather than this quite different refugee from an optical bench. To suggest the Etalon arrangement is a filter - which the sales blurb does - is like equating a Newtonian to a Cassegrain.
Still my dumb question seems to have stimulated a useful set of contributions from those who know better in what appears as a more specialist area of solar observing and helps he understand the passion here.
Why the manufacturers cant include such background in their own 'knowledge bases' beats me. Maybe the problem is their web sites are just set up to sell stuff using mainly hyperbole rather than getting people interested by explaining the fine details especially about the optics - which explain why these solar telescopes are even more remarkable achievements of mass production as their night-time counterparts... and good value for money if you can put a valid value on this in the first place.