I've been away on holiday for a short break over the Easter weekend, however the day before leaving I finally successfully completed the prototype design for a CaK filter. This filter uses 2 sets of interference filters, both centred on 394nm, however these are set slightly offset to each other in a tilt tuned arrangement to tighten the bandpass still further. An energy rejection filter is also incorporated in the optical train, prior to the tilt tuned CaK filters which enables the filter to be used with either my 70mm or 127mm refractor. I haven't got many images so far from this setup, although first impressions are very favourable. Detail levels are high, and seem to have better resolution than commercially available Lunt CaK wedges? Maybe this is a result of a tighter bandpass? The Coronado CaK setups have a 2.2A pass, where as the Lunts have a 2.4A pass.
Transmission levels are very high, and while most definitely not suitable from a safety point of view for visual observation, exposure times are in the region of 1/2000th second at zero gain @ f11 with the DMK31. This has the potential to capitalise on the moments of good seeing, and also the possibility of exploring prominences at CaK wavelengths.
This is going to prove to be a very interesting filter!!!
