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Old 14-09-2020, 01:45 PM
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Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 7,932
Spectroscopy measure of Omega/PST CaK filter

The commercial (Lunt) CaK filters are rated at 2.4A bandwidth.
I have a CaK DIY filter with five () elements:
Baader Blue CCD filter as an ERF
Three Omega Bob Ca filters
and a #1 "yellow" filter from a PST CaK
Is it as good as the bought version?
My Cak images seem to show a pretty crisp CaK network. Time to test!


Limited test...
The only available spectrograph was a Spectra-L200 with a 1200 l/mm grating, this gave a dispersion of 0.23A/ pixel
Using the normal set up with the ED80 stopped down to f10.

The bandwidth of the DIY filter is very close to 1.0 A
Bad news: due to the filter assembly "sagging" due to the added weight of the spectrograph the filter CWL was shifted towards the blue wing of the CaK line. Gaffa tape was used to "support" the spectrograph which was not successful, but at least demonstrated the effect of reducing the tilt on the CWL....it moved towards the centre of the CaK line. I can only assume at the moment that if it was properly supported and aligned to the optical axis, that the filter would be "on band" at CaK.

I need to rig up a rigid support for the spectrograph to obtain quality results. In the meantime I'm comforted by the fact the bandwidth is pretty good!
Onwards and Upwards.
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