some help req, HA solar scopes and Double stacking ??

[oldpink]

since I got my white light filter I'm loving Solar astronomy
but I'd like to take it further by moving to HA in the near future

looking at Solar scopes I see things like double stack filters costing as much as if not more than the scope
and terms like Angstrom

can someone give me an idiots guide to the basics of Solar HA imaging and what the various filters do
I assume they refine the wavelength of the viewing / imaging to bring out certain features

i'd love to image solar flares and CME events as well as use my white light solar to compliment it
working from home allows me a lot of time to do solar when I can actually see the sun

and was one of my primary interests in Astronomy in the first place

[pmlogg]

I've only used the Coronado PST and Solarmax 40 filters so I can't comment on Lunt or other manufacturers.  

The PST has a front filter for energy rejection, an internal etalon to filter out the non-H alpha wavelengths to a fraction of an Angstrom and a rear blocking filter - built-in to the eyepiece holder.  It has a mechanism rather like a helical focuser to tune the etalon, either to better view prominences on the periphery of the solar disc or surface detail.  To see more surface detail an additional Solarmax 40 filter  can be added to the front (an adapter ring is needed).  The PST suffers from limited backfocus, which can make imaging difficult; however it can be done. It is quite light and compact and can be fitted to a normal photographic tripod. And it's the cheapest of the solar telescopes. 

Coronado also does other specialist solar telescopes in 40, 60 and 90mm aperatures which come with one front etalon, rear blocking filters and a tuning mechanism.  Like the PST, they come with a solar finder and they can have a second etalon fitted for double-stacking.

Altenatively one or two Solarmax filters can be fitted to the front of a normal refractor, which must be paired with an blocking filter (either in diagonal or straight through form).  The Solarmax filters I've used have a tuning mechanism, which does what the PST helical-type tuner does.  The Coronado blocking filter designations BF5, BF10 etc. refers to the diameter of the blocking filter.   Longer focal length refractors require larger diameter blocking filters.

As you've seen, all of the kit is quite expensive, and increases rapidly with aperature.  Buying used a lot of money can be saved.  Filters can degrade so care needs to be taken.  The views could still be quite good but obviously less should be paid.

[Merlin66]

KISS.....

To see the solar Ha detail you need a very narrow bandwidth Ha filter in the order of 1A (0.1nm) for the proms at the edge of the solar disk and <0.7A (0.07nm) to really see the surface filaments and granulation details.

These are no ordinary filters and usually need three components working together to make it happen - an ERF (Energy rejection filter) to stop the optics from cooking!, an etalon filter which give the bandwidth required (they are usually designed around 1A down to 0.7A)and a final blocking filter to separate the etalon images....

Different suppliers have different arrangements - you need to check out the Coronado and Lunt offerings.

To get even MORE detail you need to further reduce the bandwidth down to around 0.5A. This is normally achieved by adding a second etalon filter (0.7 x 0.7 = 0.49A) This is called double stacking....

As mentioned the final blocking filter size needs to be at least 1/100 the focal length of the scope. For the 400mm fl PST, they fit a 5mm filter...

Hope this helps.

[oldpink]

thanks thats a lot clearer now

[Pete Presland]

get yourself a PST preferably around Dec/Jan when  a lot of people are fed up with not being able to use them much  i did one of my best and most used purchases!