COMPOSITE VIDEO (magnified x2)
S-VIDEO (magnified x2)
THE 1004x JG CCD ASTRO CAMERA
FURTHER MODIFICATIONS - OCTOBER 2003
I have made some a couple of simple modifications to the camera to improve its performance
1. Using S-video instead of composite video input to the capture card.
(Thanks to William Behrens for this idea)
In S-video, the luminance and chrominance signals are kept separate. Since the camera is monochrome, the video output is just luminance. By feeding the output of the camera to the S-video luminance input of the capture card, the filter that separates the chrominance from the luminance can be bypassed and improved resolution is achieved. The S-video luminance is on pin 1 (ground) and pin 3 (signal) of the s-video plug.
The slightly improved resolution can be seen in indoor tests taken in high resolution mode with 5sec exposures (camera cooling off) Since this is a simple free modification, I will take all my images in S-video mode from now on.
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COMPOSITE VIDEO (magnified x2) |
S-VIDEO (magnified x2) |
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2. Increasing the gain by raising the agc max gain limit
This is Jon Grove's suggested modification, published here. It is simple, involving no pin lifts or track cuts :-) and increases the electronic gain of the camera by an estimated 4-5x. Of course the noise increases as well, but as long as the same total exposure time is used for the full stack of images, the net effect appears to be to produce the same depth and quality of image using shorter individual exposures. This means any tracking errors are less pronounced and seeing effects can be reduced to some extent.
Comparison tests on M57 are shown below. At high gain, parts of the ring were over exposed in just 5sec using an 8 inch aperture! (Seeing was not good as can be seen from the poor split of the double star immediately above the nebula)
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STANDARD GAIN (7x 20 sec) |
HIGH GAIN (27x 5 sec) |
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RAW |
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STACK |
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