Jupiter on July 3rd 2006

Jupiter on July 3rd 2006
Originally uploaded by Astro Guy.

Just over two weeks ago I sat down and figured out how to couple by digital camera to my little telescope. I have two cameras. A 35mm canon rebel (takes great shots, uses film) and a digital elph 3D300 also by Canon. This discussion involves the later.

I've seen some neat images of planets created by webcams to a lesser extent by digital cameras. The idea is to mount the camera in front of the eyepiece and project the image on to the detector. This can work quite well for bright objects. For an object like the moon, you can simply point the telescope and then hold the camera with your hands in front of the eyepiece. Once you find the right angle, the moon will show up on the LCD screen. So click away. You can get some cool results!

Planets can be a bit more tricky. I have succeeded in imaging Saturn and Jupiter by hand holding the camera, but this is not ideal as even the steadiest hand will shake. The trick to getting a good image is to combine multiple images. So to help make this easier I pulled out the toolbox. I used an L-bracket and a clamp to hold the camera in front of the eyepiece. I have a f4.5 3inch refractor and I used a 2.5mm long relief eyepiece - the long relief really helps.

At this point I aim the telescope at Jupiter and put the camera into video mode. I recorded at 30 frames/sec for 30 seconds. Next I transfer the AVI on to my computer using gtkcam on Linux. I can convert the AVI into individual PNG images with the mplayer software (just use -vo png). These png images can then be converted into FITS images for the 3 seperate colours with the image magick software "convert". I use FITS format as I do astronomy CCD processing with IRAF. In IRAF you can use the immatch.xregister program to remove any x-y offsets and allign all the frames. The key parameters are to set dxlag and dylag to INDEF to use the x-y shifts from the previous image and to set regions parameter to bracket planetary image.

Once you have a set of alligned images, I compute the average of the all the frames in each colour with imcombine. This gives you a single image for each bandpass (blue, green and red). To make the final colour image, I loaded each fits file with The Gimp and made a colour composite. Then I played with the brightness levels and so forth to bring out some detail. You can see my final product above.

To really improve the image, I like to get my hands on a video capture device that outputs RAW data. No MPEG/JPEG compression. The compression routines kill fine detail. I think I could do a much better job with raw images. I've been investigating webcams, but I don't know much about right now (and I'd like one that works with Linux).