I have recently built myself a small solar prominence scope using a basic Coronado 2A H-alpha solar prominence filter. My scope design is relatively simple and uses an effective aperture of 30mm at f20. There is a deep red energy rejection filter which cuts out most of the solar light before it enters the scope, the lens is a simple 60mm f10 airspaced achromat stopped down to f20. The tunable etalon which is sandwiched with a light blue BG38 glass is placed in an pivoted adjustable carrier just before the eyepiece. It can be adjusted to pick up the H-alpha line by a small screw. The design is such that it cannot ever allow unfiltered light through to the eyepiece.
I had never seen or used a prominence filter before, and after building the scope it took a few attempts before I managed to tune the bandpass correctly onto the H-alpha line. Now that I know what I am looking for I wonder how I could possibly have missed the right setting in my earlier attempts.
I have not perfected a way of photographing the limb detail visible with the naked eye. I found that my digital camera was very unhappy with the pure red light image and it caused some most peculiar colour pixelation effects. The images are severely limited by my afocal technique with the video camera and the resolution of the video capture hardware. However they do show a nice prominence.
There was a fairly nice eruptive prominence at around 1500 UT on Friday 25th May 2001 - the first large one I have actually seen since building the scope, and I was determined to record it somehow. These images are captured from a video taken with the video camera looking into the eyepiece on a rather windy day!
The video camera also has to over expose the solar disk to reveal detail in the prominences, but unlike the digicam it does not go haywire and create fictitious colour mosaics from the noise. There was a lot more fine detail visible in the wisps through the eyepiece, but I could not capture it with the video camera. The wide views are with a 26mm Meade SP, and the closeup with a Televue 17mm - relatively short eyerelief made coupling the camera to the system rather tedious and the makeshift nature of this camera setup leaves much to be desired.
|
|
This is a colour retouched version of the video capture which attempts to give an idea of the visual large brightness contrast between the solar disk and the prominence detail. The radial jet at the base of the prominence was very pronounced, and there was a compact very bright knot of emission also visible in the same field. |
|
|
This is how the video captured frame looked raw. Colour saturation has been lost in all the bright regions. This false colour effect makes the limb prominence stand out more obviously. There is a faint spurious solar disk reflection visible that was due to an unblackened shiny steel nut in my scope. I paid more attention to safety interlocks than I did to painting every last bit of the internal optical path black. I expect contrast can still be improved. |
|
|
This is a frame centred on the eruptive prominence showing a jet going out radially and then drifting away to the side. There was a bright knot at the top of the jet where the outflowing material turned back on itself and a then long smoke trail with lots of fine detail visible in it. |
This was the first time I had seen a decent sized prominence and I had intended to report it on s.a.a later in the evening. I was therefore most surprised that when I looked again at around 1830UT the prominence had almost entirely dissipated and only a few fine curved wisps of emission were left falling back towards the sun.
