Long Exposure, Chambers's Convertion of a

Trust Spacec@m 200 CMOS webcam.


This modification was developed by Stephen Chambers.

Details 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 S.J. Wainwright.

FIRST LIGHT September 7-8, 2001

The remounted, modifed camera

Remounted camera fitted with a Mogg adapter, a switch to disable long exposure mode and the exposure control knob. Camera fitted with a Mogg 0.66 focal reducer and a Mogg parfocal ring, configured to attach to the telescope.

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.

AstroVideo, showing the real time window on the left and the result of a darkframe-corrected group of 5 integrated 4s exposures on the right


The final result

The sum of 5 x 4s darkframe corrected exposures

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.)


SECOND LIGHT September 8-9 2001

The camera was mounted at the Newtonian focus of a 12 inch, f/4 Newtonian.

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.

AstroVideo as it captures a group of 5, 4-5s exposures 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.

The sum of 60 groups of 5, 5s exposures of M13


The sum of 30 groups of 5, 5s exposures of M57



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.

S.J. Wainwright

Sept 10, 2001