2007 – New Home, New Scope, New Challenges

 

In May 2007 we decided to sell our house in the ‘burbs and move to a condo in downtown Tallahassee.  The kids had gone to college and we were racking up huge energy bills as well as suffering through a lousy commute to work.  Our new abode is 1.5 miles from work, and a pleasant walk.  The condo is on the 7th floor, and facing the major road in town:

 

 

The above view shows the adjacent Bankruptcy Courthouse (could come in handy!), central park, and adjacent hotel.  In the distance is another condominium in town. The sunsets can be quite spectacular:

 

 

As you can tell, our condo faces West.  I donated my old telescope to the Tallahassee Astronomical Society, since I had no place to put it in our new home.  Furthermore, I figured the light pollution of downtown would pretty much prevent any astrophotography.  Also, the FSU football stadium is directly West and they keep high-powered sodium lights on 24/7 (regardless of whether it is being used or not).

 

However, I read an article where NASA was using video imaging from land-based telescopes as a means to compensate for atmospheric distortion.  Due to the nature of such distortion, individual frames collected at 30 fps will generally be in focus, but longer exposures will be fuzzy.  So, the process involves taking video and then aligning each frame and summing the images.  This requires an extremely sensitive video camera, fast lens (<f2.0), software for stacking, etc.  Amateur astrophotography has been utilizing this approach for planetary imaging.  In this case, the planets are quite bright and good images can be taken with insensitive video cameras and slow lenses.  However, Watec has recently developed a sensitive video camera for amateur astrophotography.  Furthermore, one company (Starizona Inc.) has developed a modification to consumer Schmidt-Cassegrain telescopes that converts them from f10 to f1.8 lenses.  The combination of the two could permit videoastrophotography at an affordable price.  This technique also does not necessarily require an accurate tracking mount.  I decided to try to see if this method would work, and started by purchasing the Watec video camera.  It needs a lens so I purchased a reasonably fast (f2.8) lens from ebay.  Here is my new “telescope”:

 

 

Pretty tiny compared to my prior scope, but it will allow me to test this new method of astrophotography.  One of the first problems was that the lens would not come to focus.  The Watec camera appears designed for telescope use, where there is much more range of focus.  The lens is from 16mm video cameras and assumes a precise focal plane distance.  Anyway… I had to file down the adapter on the telescope to get the lens in focus.

 

Next I took several test videos, and this identified various other issues associated with file size (huge – on the order of Gigabytes after only a minute of video), video compression artifacts (lossless compression results in larger files but is essential to astrophotography), file format compatibility with image stacking software, and so on.  I tried various compression codecs, different capture software, and different image stacking software, and found the following to be best:

 

Capture software: VirtualDub (www.virtualdub.org)

Frame decimation software: VirtualDub

Image stacking software: Registax (www.astronomie.be/registax/)

 

The Watec 120N+ (StellaCam3) video camera allows on-chip integration of various multiples of frames (i.e. 1, 2, 4, 8, 16, etc.) all captured at 30 fps.  The raw video remains 30 fps, thus, if the camera setting is to integrate 8 frames, for example, the video does not output at 4 fps, but simply duplicates the last integrated image at 30 fps until the new one is ready.  Thus, the video (in the case of 8 frames being integrated) is 8 times larger than it needs to be.  Registax has a size limitation of 10,000 frames in the loaded AVI file and this limits the file size (exposure time).  The VirtualDub software has a “decimation” feature where you can specify how to sample a captured video file (in this case, decimate by a factor of 8 to eliminate duplicate frames).  This worked pretty good.  The VirtualDub software also save video in a lossless AVI format that can be read into the stacking software.

 

The following is a single frame of video at 0.25 sec exposure (8 frames integration at 30 fps):

 

 

The following is a stacked image composed of ~2400 frames:

 

This looks really promising.  One thing I found was that at 100mm focal length (i.e. the focal length of the lens) the image moves off-screen due to Earth’s rotation after about 5 minutes.  Thus, while a mount is not necessary for a sharp image, you still need to track the object to keep it in the imaging frame.  Thus, an equatorial mount is still necessary from a practical standpoint.  I have not yet decided which f1.8 optical system to purchase (they are expensive), I think a mount will be necessary.