Dec 13th: More H-a-musings.

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Here's a token live video from my heavily modified, 6" f/8, H-alpha telescope. The seeing wasn't particularly good and the thermal agitation, caused by the intervening atmosphere, is self-evident. ZWO ASI174MM [mono] camera. It is views like this which drive me on to continuously improve my solar instrumentation. Solar imagers use videos like this to produce high resolution "stills." Usually adding false colour.

It has been grey for a few days so the discussion on H-a instrumentation goes on. My plan was to add a full aperture D-ERF to my 150/8 OTA to reduce internal heating..

Quote from Baader sales website:  "Our 43-layer dielectric DWDM-coating delivers a COOL-beam of pure red light, with a HBW of 80 nm!"

I had a very interesting response on Solar Chat! forum to my worries about heating effects inside the D-ERF filtered telescope. BobY analysed the heat passing through the "cool" full aperture, Baader D-ERF with startling results. He went so far as to suggest adding [potentially sacrificial] protective blocking filters before the etalon. I can vouch for the warmth of the red focused beam after it passes through my sub-aperture D-ERF and the PST etalon. The Etalon sits in that hot beam for countless hours quite close to focus!

My habit of tracking the sun all day long, on sunny summer days, may well have been stressing my PST etalon. It was a danger I never really considered seriously. Replacement of the PST etalon is a ~£500 bet on getting a good, secondhand one from any random, PST, donor telescope purchase. With rather doubtful odds according to some experienced PST users and H-a telescope modifiers. Some PST etalons are excellent but do seem to be very few and far between. There are even reported to be PST etalons, which are so poor, they should never have left the Mexican factory.

Without a suitable comparison I cannot be sure where my etalon lies in the quality spectrum. It has given me a lot of H-a fun. So I'd hate to think I have damaged it by naively believing Baader's sales propaganda at face value.

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