Friday, June 22, 2012

Travellers solar setup

Today I practiced using the small solar H-alpha setup I will be using for our upcoming trip to Mallorca and - later on - to Australia for the total solar eclipse of 2012. I also used this setup for shooting full disc views of the recent Venus transit and that went well. It features a Coronado SM60/BF10 0.7Å H-alpha filter, f=420mm ED refractor on an AstroTrac mount.

This time I wanted to have a go at some more resolution, so I plugged in a 4x powermate. The optical resolution of the 60mm aperture H-alpha filter is around 2.3". The effective focal length of my setup with a 4x powermate is around 1700mm; hence the image scale on the Skynyx 2-2M camera is 0.5"/pixel. I will thus be oversampling the optical resolution by a factor ~4 at 1x1 binning. If needed I can use 2x2 binning and oversample by a factor ~2. I should therefore be able to get close to the maximum possible resolution with this aperture.
Travellers solar H-alpha imaging setup
Setting up is quite fast since polar alignment isn't really that important for this kind of work. In addition, everything is light and small - unlike my other setup which uses a Tak EM200 mount and a 6" refractor. In order to reach focus a 2" diagonal has to be inserted before the rest of the imaging train. The whole arrangement pressed the Crayford focuser and mount pretty hard, but I could still focus and navigate around the solar disc. I am using the Baader Stronghold for holding the scope and enabling fine-tuning of pointing. It was not the completely smooth, solid experience you get with the EM200 mount - but that thing isn't about to sneak on as carry-on luggage anytime soon!

The Sun was pretty quite today and it was late in the afternoon, but I still shot some 1500-image sequences of  a pair of prominences. Stacked best 60 frames using AviStack, wavelet filtered using Registax, and colorized in Photoshop - see results below.
Best 60 out of 1500 frames; 20msec exposure time with gain=3

Best 60 out of 1500 frames; 5msec exposure time with gain=7

Now I just need to foam pad a small carry-on airline suitcase and I am ready for take-off to Mallorca next week!

Wednesday, June 6, 2012

Venus transit 2012

Had a fantastic transit experience at Charlottenlund Fort, Copenhagen! Will be posting some pictures here as they are processed - stay tuned. Become a follower of this blog to get updates automatically.

Sun had just cleared clouds at horizon.
I'm at work right now and better get back to it!!
Home from work, get Astrid in kindergarten, go to playground, make dinner, wash floor. I am pretty tired now - I only got two hours of sleep in the past 36 hours. I just got to try and process some data from my new solar telescope. I only got time to try it ONCE before the Venus transit. Just did some basic processing; see result below (click here for full resolution). I am HAPPY! Will play more tomorrow, but now I'll go to sleep with a smile.
Venus with a small protuberance - just before the show ended.
Had a terrible headache yesterday, which I often do after going all-out for some crazy event. Today I feel fine and I tried to see if the refraction of light in Venus' atmosphere was captured in some of my images. The setup I am using with a H-alpha filter is not optimal for this purpose - it transmits a very small fraction of the Sun's light, forcing me to use long exposure times which in turn will be more susceptible to blurring from our own atmosphere. I think that a white light filter would have been better. Anyway, between third and fourth contact I tried shooting at several (longer) exposure times:
Changing the exposure time to catch a glimpse of sunlight refracted in the atmosphere of Venus
Looking closely at the image with the longest exposure time I can just barely make out a faint arc of light that follows Venus' limb! It is visible for roughly 30 degrees across the north pole of the planet. I tried manually selecting the best images in the sequence, then stacking and tweaking curves. I also applied a DDP filter and unsharp mask to enhance the arc further - see the result below.
Processed image revealing sunlight refracted in the atmosphere of Venus.
This sighting is nowhere near the quality obtained by others in 2004 - I think this is due to the low altitude of Venus as seen from this part of the world. For the ultimate view of this effect check out this image from the Hinode spacecraft!
Working through all the images I took on June 6th I have now completed basic processing of all the image sequences - 27GB in total, consisting of 24410 individual images. 'Basic processing' means using Registax v.5 to sort, align and stack with a focus on the disc of Venus. The Venusian disc will then be sharply defined, but orbital motion of Venus will cause a slight blurring of the Sun. I therefore do a second processing run using AviStack v.2 and focussing on the solar surface while ignoring Venus. I typically stack 60 images since this (in my experience) is a good compromise between using only the sharpest images and keeping the noise level down in the final result. Each stacked image is sharpened using wavelets, then the two are combined in Photoshop to get both Venus and the solar surface sharply defined. Final touches include colorizing the image and tweaking of levels and curves. My latest result is shown below - taken at precisely the moment of third contact (full resolution is HERE). The resolution, contrast and colors are better than on the previous close-up view shown above - maybe because the first one was made in a zombified state of fatigue..!?
Venus transit - moment of third contact.