GStar-Ex Camera Imaging Technique
|
The GStar-Ex video camera is a comparatively inexpensive entry-level unit. But it is quite versatile being able to image both Solar System and faint deep sky objects. It is well suited to persons wishing to dip their toes into the fascinating world of astro-imaging.
The camera has a standard output of 25 frames per second. It is cable-linked to a laptop computer. The laptop uses an image capturing program specifically designed for the video camera. The program displays the video camera's output signal in real time so you can see exactly what the camera is aimed at. The camera has a wide range of exposure settings and its output can be augmented by increasing its “gain” setting (roughly the equivalent of using a faster film speed). At the fast end, exposures range from 1/12,000th to 1/25th second. Alternatively, for imaging faint objects, the camera can accumulate the light signal it receives from the telescope each 1/50th second and output the result as a single frame only after a nominated number of accumulations. The available accumulations range from x2 up to x128. At the maximum setting of x128 light is accumulated during 2.56 seconds and it takes almost 13 minutes to capture a 300 frame video clip.
The camera only images in black and white. Nevertheless colour images can be created by imaging the same subject a number of times, each time using a differently coloured filter in front of the camera's CCD. Luminance, red, green and blue Baader filters were held in a rotating manual Atik filter wheel for this purpose. When the results of each of these L, R, G and B video clips were combined they produced the required coloured image.
No fancy auto-guiding equipment was used. Just good old fashioned manual guiding – with a modern twist. The image capturing program allows a set of cross-hairs to be positioned over a star in the camera's on-screen live view. Once a video capturing run was started the star was constantly monitored by eye and if it drifted away from the centre of the cross-hairs the capture was paused. The star was then repositioned back to the centre of the cross-hairs using the telescope's control pad and the capture was resumed.
Post-processing involved stacking the individual frames in the captured video clips to produce a single image from each clip, combining L, R, G and B images (if colour images were required) and enhancing images to bring out faint details
The camera has a standard output of 25 frames per second. It is cable-linked to a laptop computer. The laptop uses an image capturing program specifically designed for the video camera. The program displays the video camera's output signal in real time so you can see exactly what the camera is aimed at. The camera has a wide range of exposure settings and its output can be augmented by increasing its “gain” setting (roughly the equivalent of using a faster film speed). At the fast end, exposures range from 1/12,000th to 1/25th second. Alternatively, for imaging faint objects, the camera can accumulate the light signal it receives from the telescope each 1/50th second and output the result as a single frame only after a nominated number of accumulations. The available accumulations range from x2 up to x128. At the maximum setting of x128 light is accumulated during 2.56 seconds and it takes almost 13 minutes to capture a 300 frame video clip.
The camera only images in black and white. Nevertheless colour images can be created by imaging the same subject a number of times, each time using a differently coloured filter in front of the camera's CCD. Luminance, red, green and blue Baader filters were held in a rotating manual Atik filter wheel for this purpose. When the results of each of these L, R, G and B video clips were combined they produced the required coloured image.
No fancy auto-guiding equipment was used. Just good old fashioned manual guiding – with a modern twist. The image capturing program allows a set of cross-hairs to be positioned over a star in the camera's on-screen live view. Once a video capturing run was started the star was constantly monitored by eye and if it drifted away from the centre of the cross-hairs the capture was paused. The star was then repositioned back to the centre of the cross-hairs using the telescope's control pad and the capture was resumed.
Post-processing involved stacking the individual frames in the captured video clips to produce a single image from each clip, combining L, R, G and B images (if colour images were required) and enhancing images to bring out faint details