Does anyone near me have a Stage 1 PST mod....?

[Merlin66]

Guys,

As you can see from the lengthy discussions over on the solar chat site, there's no easy answer....

The "mini-erf" ITF is not available as a stand alone filter.

The Ha "system" is made up from at least three key elements:

An ERF to reduce the total energy

An etalon to give a sub angstrom bandwith

And a sorting/ block filter to suppress the unwanted etalon bands.

[JamesF]

Ah, so the etalon produces a series of peaks and troughs across the spectrum, some where it transmits and blocks light. I looked up this:

http://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_interferometer

which is quite an interesting read.

Is it correct to suggest that the tuning of the etalon by tilting it is to allow one of the transmission peak to coincide with the H-alpha emission wavelength?

James

[JamesF]

(Apologies, Luke. I realise I'm drifting your thread rather a lot. If you'd prefer I started a new one, please say.)

James

[lukebl]

(Apologies, Luke. I realise I'm drifting your thread rather a lot. If you'd prefer I started a new one, please say.)

James

No, no. This is all a great learning curve!

[Merlin66]

The "comb" of a typical PST Ha etalon (similar for the Lunt etc) passes a narrow 0.7A band every 10A or so.

The final "blocking" (sort) filter ( around 8A bandwidth) then suppresses all the other etalon passbands just leaving the one at Ha visible.

By design the etalon has a passband just above the Ha wavelength (this allows coverage for the Doppler effect/ red wings), when the etalon is tilted (or the air pressure increased as per the Lunt) the central wavelength moves towards the blue - this then picks up the central Ha wavelength and allows observations of the Doppler effect/ blue wings.

[JamesF]

Hmmm. So even the (very expensive) Astrodon 3nm filter wouldn't be sufficient in front of the objective as the mini-ERF appears not to cut the band either side of the main Ha passband and you'd still have a 30A wide beam entering the etalon.

James

[Helen]

I suppose if it could be done in an alternative and cheaper way then the BF wouldn't cost so much.....

Helen

[Merlin66]

We're working on it....but no real success...as yet.