Saturday, April 3, 2010

Experimenting with the active Sun

Looks like the Sun has finally woken up. After a longer and quiter than usual solar minimum active regions, sunspots and large prominences are back. I have tried in the last few months to image the Sun through Cosmic Journey's Coronado Personal Solar Telescope (PST) using my Canon XSi. The problem I found very quickly is that I could not use the camera at prime focus using the Orion Universal Adapter as a means to attach the camera to the scope. Of course I could have purchased a shorter adapter or maybe even built one, but I am in no mood of throwing money at the hobby nor I have much time these days, plus I enjoy the challenge of figuring out how to achieve what I want with what I have. Adding Barlows and Powermates in an attempt to bring the focal point further back didn't solve the problem. Then I realized that somewhere in the basement I still had one of those cheap brackets for afocal projection. The bracket comes with a clamp that holds onto the eyepiece which is not really the best solution for a scope as small as the PST given that the bracket plus the camera is probably as heavy as the scope itself. On the other hand I can reach focus with afocal projection so I gave it a try using the standard Kellner 20mm eyepiece that comes with the PST.

A very large prominence located in the North polar region of the Sun has been in sight for a couple of days. When I looked at it visually on Fri, April 2nd it looked really nice. Other smaller prominences were also visible off the solar disk roughly diametrically opposed to the large prominence. There was also an active region with sunspots (AR1057) and a another one sporting a nice filament (AR1059). Here are a series of images in white light and Hα taken by two RASC fellow astronomers:
Paul Campbell
Denis Fell

Here is my image. The good thing about the Canon is that the sensor is large enough that even at 800mm focal length I can frame the whole Sun. The PST is 400mm in focal length, but I used a Barlow 2X. Without it the Sun turns out too small for my personal taste. Actually when used at f/20, the PST and my Canon are a really good combo: good detail, good colours and the size of the Sun on the sensor is just perfect. Since this was the first time I succeeded at imaging the Sun this way, I played around with exposure time and gain (ISO). It turned out that the prominences were best visible at 1/125th sec exposure and ISO 1600. I took 10 frames which I stacked in Registax to increase the Signal-to-Noise ratio of the final image. For the disk I used 1/125th sec exposure but I lowered the ISO to 100. That allowed capturing the filament and the active regions which would otherwise wash out if the solar disk were too bright. For the disk I stacked 10 frames in Registax as well. I reduced the size of the frames to 1280x960 to make Registax's life a bit easier. To combine the the final frames (the one with the prominences and the one with the disk) I imported both images in Photoshop and used layer masking to combine the two images. I also sharpened a bit the two final images before combining them together.

Overall I am pleased with the result. There is still some room to play while processing the final product. I am sure I will have quite some fun with the Sun in the next little while!