This modification was developed by Stephen Chambers.
of the modification are on Steve Chambers' website
A modified .SET file replaces the .SET files provided with
the driver software.
The camera modifications were carried out by D. Francis and
The camera, configured as above was placed at the prime focus
of an f/5, 80mm refractor, and driven in RA.
As the CMOS camera is an inherently insensitive imaging device,
the scope was pointed at the very bright star Vega, which was visible in normal
mode, but no other stars in the field were visible.
The COAA AstroVideo software was used to integrate frames captured
from the modified camera.
The Variable resistor was turned until the on-chip integration
time was about 4s.
AstroVideo was set to collect 10 groups of 5 summed, 4s frames
with the scope covered.
This produced 10 integrated darkframes.
The 10 integrated darkframes were then summed by the fixed
sum function in AstroVideo. This produced a single darkframe which represents
the sum of 50 x 4s exposures. The darkframe is shown below.
AstroVideo was then set to use this darkframe, scaled by a multiplier
of 0.1 and to automatically subtract this frame from groups of 5 integrated
4s image exposures, for both display and saving.
The sum of 10 x 5 x 4s darkframe corrected exposures.
The Auto register and sum function
of AstroVideo was used to sum the 10 Fits files,
each of which comprised the sum of 5 x 4s exposures, (one such image
is shown on the left.)
The camera was mounted at the Newtonian focus of a 12 inch, f/4
The exposure was set to give 4-5s per exposure.
AstroVideo was set to integrate groups of 5 exposures and to
collect 30 groups of M57 and 60 groups of M13.
Note that the real time video window shows nothing of the M13
which is hidden in the dark noise. The image on the right is 5 such frames,
summed and darkframe subtracted. The brightness of the right hand image is
just for display and is the result of an automatic scaling algorithm to display
the image as is is produced.
A combination of Off-Chip video integration using the COAA AstroVideo
software and 4-5s on-chip integrations allowed this relatively insensitive
CMOS camera rated at 2.5 lux, to image stars and some deep sky objects.
This experiment demonstrates that it is possible to achieve
'long' exposures from video devices by making relatively simple hardware and
software modifications. Moreover, Off-chip Video Integration can then be used
to synthesise even longer exposures, revealing fainter objects and increasing
the signal/noise ratio.
Sept 10, 2001