The speaker for the November meeting of the St. Louis Astronomical Society
will be SLAS member Jim Melka. Jim will show his latest photographs
of Mars and walk us through the process of digital imaging. This process
has greatly enhanced the capability of amateur photography resulting
in high quality images.
Jim Melka has been observing and taking pictures of Mars since 1971.
But, there has been a big change this year, he has switched from using
film to digital imaging. Instead of taking 36 images in a photo session,
now the number usually ranges between 200 and 400 images. A 6.3 mega-pixel
Canon D60 digital SLR camera body captures the images. Eyepiece projection
is still used, but it has been possible to increase the projection distance
from the eyepiece to the recording media, thus increasing the magnification.
The exposure time was 1 to 2 seconds with film, but ¼ second
exposures are now used, thus lessening the effects of seeing conditions.
Computer processing allows combining selected images to produce an enhanced
result over what is contained on any of the individual images. The process
is called “Stacking” and a robust freeware program called
Registax is used to automatically align and combine selected images.
The real details are reinforced while noise and other artifacts disappear.
The next step is to apply an unsharp-mask filter on the stack-image
to extract hidden details. It takes only about 45 minutes or so to record
the images with the telescope, but selecting the best images to stack
plus the computer processing can take upwards of 2 hours or more. Digital
imaging can be done with any size scope and will produce results far
beyond what would be expected. It can be a very rewarding experience.