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A description of Fastar technology (by Robert
Berta)
All
of the Fastar images on this site were shot from my backyard which is in an
area 1/2 mile South of San Francisco and about 3/4 mile from the Pacific
Ocean....hardly a dark sky spot! The setup I use is a Celestron Fastar equiped
8" SCT Deluxe. This is a unique SCT that allows the user to easily remove
the SCT's secondary mirror and replace it with a Fastar Optic Assembly. This
assembly in turn allows for direct connection of a SBIG 237 CCD camera at the
front of the scope rather than the traditional rear position of a SCT. This
option converts the scope into a 8" aperture - 16" focal length
Schmidt camera of f1.95 speed. This allows for very wide imaging by CCD
standards.... .5 x .7 degree FOV....and also very short exposure times.
Exposures are about 25 times shorter than at F10 position. The fast speed and
lack of any reciprocity (films need to increase exposure by large amounts to
compensate for much longer exposures) allows me to image shots in seconds that
would take an hour or more on film. If
you are wondering....no....you can't visually use the scope with this setup. It
requires use of the computer laptop in real time to scan the heavens. I use
digital setting circle to find the objects....or use my 8x50 finder scope. I
can set the software to repeatedly take a short exposure of around 2-3 seconds
and autoupdate the screen image. This allows for an ongoing "show"
that anyone can see on the laptop screen. By the way....the 2-3 second image is
equivalent to the visual view through a 20" scope. The conversion between
standard SCT and the Fastar takes just a couple of minutes. A heavy duty
secondary keyed location setup ensures the secondary goes back in the exact
same spot and I am amazed the it maintains its colimation nearly perfectly
every time!
I am a newbie at CCD imaging having had this setup for about 6 months....and
color ability about 1/2 of that time. But I found this equipment to be far
easier to use than my old Off Axis Guided Film stuff with a lot less
frustration also! In particular I am impressed with the seemingly little effect
that light polution has on the results compared to film....and the ability to
capture extremely faint stars. A 60 second exposure will capture down to a mag.
18.8 star under dark skies. Color
shots are taken automatically with the motor driven RGB filters taken
sequential B&W shots. The software than allows you to combine those three
shots to make a color image. You can enhance the shots by the included program
or higher end image manipulation programs like Adobe PhotoShop.
The software allows one to determine the longest exposure time before "egg
shaped" stars due to star tracking inaccuracies. You than either don't
exceed these times for single shots or perform what is known as "Track and
Accumulate". This is a software provided option that takes multiple
exposures each of which is short enough to avoid the star trails. The software
than automatically stacks the images and registers them to equal the equivalent
of a single long exposure. This tool allows you to utilize less than excellent
drives to capture excellent images. This means no more of the manual long
guiding necessary for film photography....unless you have a CCD autoguider. By
the way....if you still insist on doing some film photography the CCD Camera
can do duty as an excellent autoguider.
The shot of the Dumb Bell Neb. was taken the night of the SFAA picnic. As you
can see, not only doesn't light polution bother the shot very much compared to
film....but the full moon wasn't an issue either. On the Owl and Ring Neb. you
can see the illuminating stars and the owls "eyes".
While CCD images are great for viewing on computer monitors or small prints,
film based photography is still the champion for large print sizes....but it
won't be long before CCD takes over there too!
Currently only Celestron's 8" Celstar SCT Deluxe, 8" Ultima (GoTo
scope) and the 14" SCT have the Fastar option capability.
Since it is a relatively new product and Celestron hasn't done the best job of
promoting it, users are not yet numerous....but hopefully that will change once
the word gets out. Robert Berta
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