Sunday, November 3, 2013

Solar imaging take two

A week has passed since I first tried out my new ASI120MC camera, and I was able to image two targets with the camera over the past 24 hours:  Venus yesterday evening, and the Sun this morning.  Seeing conditions were variable last night as I attempted to capture Venus.  I have a very small window from my observatory where I can actually observe Venus around sunset before it quickly passes behind a tree in my neighbors yard.  Venus is inherently a difficult target to image in the evening skies as it is generally not more than 20 degrees above the horizon, and last night there were also clouds rushing in from the west.   As I live east of Tucson I am also looking right over the city when I observe to the seeing conditions for evening apparitions of Venus are always a mixed bag.  I did manage to create the image below and it was my first attempt at using a cheap 2x Barlow lens with the camera.  In order to reach focus I also had to use a mirror star diagonal, which is likely not ideal for imaging.  Below is the result of stacking about 150 usable frames (out of 2000) and some processing in Registax.

While I was hoping to do some visual observing last night and ultimately try to image Jupiter, the aforementioned could bands rolled in and we were treated to a long steady rain lasting until near midnight.  This morning skies were mostly clear with some passing thin cirrus and as the coffee was brewing I set up my 60mm Lunt HA scope to try and create another solar image.  Seeing was fairly steady and other than the passing bands of cirrus I was able to take an avi of approximately 2000 frames.  The result is below, following a stack of about 750 frames and some processing in Registax.

In some ways, this image is better than my previous attempt.  Clearly (pun intended) the improved seeing conditions helped me to start with better data and more usable frames.  Having steady skies also made focusing a bit easier.  I also happier with the sharpening and denoising I did using the wavelet functions in Registax, although I could still be more effective with these techniques.  The exposure settings were not ideal as some of the active regions are a bit washed out and I also did not have the etalon filter on the telescope tuned as precisely as I would have liked.  While I had it tuned for the eyepiece I was using prior to image capture, it seems that it needs to be tuned slightly differently for the camera. This tuning process as well as precise focusing is something that I need to continue to explore if I am to improve the images.  If I had to rank the importance of these factors, focusing is probably number one, followed closely by the tuning, with the atmosphere being the third consideration (and the one I have no control over).  As I become more fluent in the exposure time, gamma, and gain rate settings, I will be able to compensate slightly for the atmospheric stability being less than perfect.

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