Monday, 27 May 2013

AR11756 Hi Res Cak 26th May

AR11756 Cak by Mark Townley
AR11756 Cak, a photo by Mark Townley on Flickr.

I'm away on holiday at the moment on the Pembrokeshire peninsula in West Wales, and for once are surrounded by miles in each direction by fields and trees, go further than that and are surrounded by the sea. This is quite clearly having a positive effect on the seeing conditions, certainly compared to ring of concrete, tarmac and roof tops that encircles me for miles and miles back home at Brierley Hills. I was set up and observing by 7am and as soon as I could see the image on the screen I knew the seeing was exceptionally good, and so using the Televue 2.5x powermate upped the focal length with my 100mm refractor to 2500mm; normally i'm struggling at half of this... By using the lunt solar wedge with no neutral density filters as an ERF I am able to keep exposure time short, however I think if I pushed the focal length any longer I really would have spoiled the image with longer exposure time causing smearing as a result of the seeing. This setup is allowing a 5% energy pass from the solar wedge at CaK wavelengths, but to keep exposure times as short as possible another route is going to be needed; one possibility is to use an UV hot mirror from Edmunds optics. This would provide an OD3 block of wavelengths longer than 400nn, but would allow transmission at 393nm in excess of 95%. At focal lengths in excess of 2000mm this extra light could be very useful at freezing the seeing. I have recently discovered if it possible to keep the exposure shorter than 1/1000th of a second, this really does allow a higher quality of frame to be recorded, I have found this to apply at both CaK and white light (540nm) wavelengths. Another experiment to pursue!