Sunday, 31 July 2011

Ha Full Disk - 31st July (Flats & Darks Update)

full disk colour final by Mark Townley
full disk colour final, a photo by Mark Townley on Flickr.

Well the weather for me of late (read this summer!) has been diabolical - the weathermans definition of fine sunny weather seems to be lots of clouds with the sun poking out now and then. This isn't much good for solar other than for a quick glimpse visually, and is certainly no good for imaging.

I was pleased to see this morning clearish skies, the milkiness had a tinge of blue to it, so I decided to go and get the solar kit setup. I was initially none too optimistic about what the results would be like, but as I processed the FITS files in Registax for wavelets I was pleasantly surprised at what was coming out.

There is a real show of active regions spanning the northern hemisphere on the Earthward side of the sun, with associated flaring and filaments to boot. The haze obscured the proms visually but they came out ok in the end on the image.

This was made using dark and 'pseudo flat' frames, and from my perspective the biggest impact these are having on my images apart from the removal of banding and dust motes, is how evenly illuminated the frame is. More subtly is the spicule ring around the solar perimeter is much more obvious. 40mm aperture isn't going to resolve individual spicules, however it is clearly visible whereas previouslly was not.

I'm officially now 'on holiday', so weather permitting should be able to get images up on here more often!

Sunday, 24 July 2011

Ha Full Disk - 24th July: Update on Flats...

full disk f26 lrg by Mark Townley
full disk f26 lrg, a photo by Mark Townley on Flickr.

After weeks of poor weather here in the West Midlands this sunday was a day with gloriously clear skies, deep blue, and in the morning with good seeing conditions too.

I decided to try out my new 2.5x Televue Powermate; this is an excellent piece of glass as I expected and shows lots of promise. The image here is a 12 pane mosaic constructed in IMerge. I used both a flat and dark frame for this, and it is clear that using these is solar imaging is a positive way forward. The image is very even in terms of illumination, and displays much finer detail than with not using the flats and darks. These will be a standard part of my solar imaging process now.

This was taken with the DS40 @ f26, DMK31 camera.

Sunday, 10 July 2011

Ha Full Disk - 9th July: Using Flat Fields...

ha full disk b&w by Mark Townley
ha full disk b&w, a photo by Mark Townley on Flickr.
There has been some discussion of late on the Cloudy Nights Solar forum as to the use of flat fields in solar imaging. My DMK31 chip is generally kept spotless in terms of dust and other contaminants, so have no use for a flat field there. However various lenses I use are susceptible to the diffraction effect known as 'Newtons Rings', this manifests itself as a series of light and dark bands across the image caused by interference patterns generated as a result of working in monochromatic light. In addition there is also a fainter (but still there) banded pattern that appears to be etalon related. I knew that a flat field should remove both of these banding artefacts.

The purpose of a flat field is to generate an image that can be 'subtracted' from your final image that removes all artefacts caused by variations in pixel to pixel sensitivity, plus any distortions in the optical path.

Generating a flat field was relatively simple: as I was imaging using a barlow it is possible to image the very centre of the solar disk. Defocussing removes all detail that is present on the solar disk, but all the banding artefacts remain easily visible. An AVI is taken of this which can then be fed into Avistack2 during stacking.

This image is the result: There is no banding visible and the frame as a whole is very evenly illuminated. Bear in mind, this is a 6 pane mosaic also. Fine detail is also greatly enhanced. I'm really pleased with this, and next time the sun cares to return I will also take a dark frame and include this in the processing workflow.

Hope you like it!

CaK Full Disk - 9th July

cak full disk f18 by Mark Townley
cak full disk f18, a photo by Mark Townley on Flickr.

Low activity is echoed at CaK wavelengths, however there is always something to see!

White Light Full Disk - 9th July

wl full disk f20 by Mark Townley
wl full disk f20, a photo by Mark Townley on Flickr.

Activity on the sun, while there, is still generally very low. There was a smittering of spots on the suns surface yesterday but nothing spectacular. Still, it made for a nice full disk mosaic. 6 panes assembled in IMerge with the 70mm frac at f12, Lunt solar wedge, 705nm TiO filter and DMK31 camera.