testing of the PST and SM60 etalons

[Merlin66]

Managed to get the five minutes of sunshine needed to set up the Spectra-L200 (1800 l/mm grating 0.2A/pixel) with a PST etalon, a SM60 etalon and a couple of Coronado blocking filters.

I did n't have the SM60 fixed to a scope, just hand held infront of the spectroscope and my shaking hand caused some spreading of the bandwidth. I'll repeat the experiment with it in position on the ED80.

Summary:

The finesse of the PST and the SM60 is very similar (10A) and the blocking filter has a bandwidth around 5A - so a good match.

I'd love to borrow a couple of Lunt etalons/ BF to compare....

1710_sm60_04_hand_5s.bmp

1710_solar03_1s.bmp

SM60_bf01_1710_15 sec.bmp

SM60_bf02_1710_15 sec.bmp

[Jack Martin]

Merlin,

Interesting results.

Jack

[hunterknox]

Interesting indeed.

I'm sure the answer to this is 'no' but I can't figure out why - is there any reason why something like an astrodon 3nm narrow band Ha filter couldn't be used as a blocking filter with the PST etalon + ERF. Internal reflections, perhaps?

[Merlin66]

The bandwidth of 3nm is 30A, the finesse is around 10A so you need something< 10A (<1nm) to be effective.

Sorry it wouldn't work.

[hunterknox]

Aah, of course. I'm mixing up my angstroms and my nanometres. Thanks Merlin.

[PeterW]

....I guess there is the tradeoff of making a low finesse etalon and a costly blocker and the otherway round. So the etalon ends up such that it is not impossible to make and the blocking filter ends up more expensive that more common astro filters are......

Good work

PEterW