I developed an alternative circuit based on Steve Chambers's Advanced Mod which can easily be implemented without the need for the extra PC board. In fact, it can be built so compact that it can all fit back in the egg. An added advantage is that the wire lengths are very short, minimising the addition of noise.
This view taken during the modification of camera #2 reveals another "secret" of my compact implementation - the use of a SIL (single-in-line) resistor pack hanging off the side of the "dead bug", taking care of 7 of the 8 resistors in the circuit.
A close-up view after modifying camera #3 clearly showing the "dead bug" glued to the control board and the amp-off transistor on the back of the CCD board.
This is what the front of the CCD board looks like with pin 9 lifted.
This was a first-light image with my version of Steve's Standard Mod with camera #1. A 30 sec exposure taken in a completely darkened room (yes, we don't have streetlights here at the Observatory). The only illumination was from the PC monitor, only set bright enough to make out the DESIRE controls.
This 120 second dark exposure before the amp-off transistor was added clearly shows the dreaded amplifier glow.
An identical 120 second dark exposure after implementing the amp-off transistor (to pin 9 of the CCD) effectively took care of all amplifier glow.
A 30 second exposure under the same lighting conditions as the first-light image above. The reflection of the dimmed monitor and the LEDs of a radio on the cupboard show up brightly.
One might mistake this for a daylight scene but this picture was actually taken at midnight under near full moon conditions. A 10 second exposure was enough.
All the above pictures were taken with the standard Vesta lens. During previous experimentation with the unmodified Vesta, I made up a set of adaptors to enable standard camera lenses to be fitted to it. By mounting the camera on my old satellite tracking mount, unguided astronomical pictures could be taken.
The moon is an obvious first target while setting up the mount. The mod had to be disabled for this picture (by simply unplugging the printer port cable) because the moon is so bright.
Fitted with a 55mm f/2.8 lens, this 20 second exposure shot of Orion's Sword shows up M42. An aeroplane crossed the field during the exposure, highlighting a problem in the lens mount casting of the Vesta - the thread holding the lens is not exactly square to the CCD, making exact focussing over the whole field impossible. This was later changed with a better made casting from another camera. Severe trailing so close to the equator on an unguided mount is very noticable.
Aiming the camera, still fitted with the 55mm lens, closer to pole at Carina and exposing for 10 seconds, star trailing can be reduced to almost nothing. The colours of the nebulae become apparent.
In order to obtain longer exposures without trailing, the camera was mounted on a Celestron C11. Unfortunately, a faulty handset caused the tracking speed to be incorrect and all the exposures had to be manually guided.
Moonlit nearby domes make good targets for setting up. Only 13 seconds exposure was enough. Lens: 28mm f/2.8
The great southern globular cluster, Omega Cen reveals itself as a fuzzy blob with the 28mm lens after 20 seconds.
Exposures of 40 seconds starts showing skyglow with the near full moon around. This picture was roughly aimed at the rich Carina region.
Our 20" telscope use standard 1¼" eyepieces and after making up a suitable adaptor, the Vesta could be fitted to it. Unfortunately, the viewing prism lever (just above the camera in the above picture) prevented the camera from reaching mutual focus with the Varo eyepiece (black eyepiece visible behind the camera). The telescope focus therefore had to be moved quite a long way, meaning the aquisition eypeice was way out of focus making it very difficult to centre on faint objects.
The plate scale of the CCD is not well matched to the telescope resulting in a very small field of view as can be seen in this shot of Alpha Cen, separated by 20 arc seconds. Due to the tremendous brighness of 0 & 1.2 magnitude of the two components, a 1 sec exposure forced a gain setting of 0.
Due to the pointing difficulties and small FoV, double stars were the best targets. Here is a 3 sec exposure of Alpha Circini. Note the nice colour difference.
Mu Crucis, a 4.0 and 5.2 mag star, 35 arc seconds apart, was another very easy target.
A little more demanding double is Xi Sco at 8 arc seconds with stars of 5.1 and 7.3 mag. The system has a third 4.8 mag component, only 0.8" away which was not going to be possible to see with the telescope being shaken around in a 60km/h wind which eventually forced me to stop observing.
The best picture was presented by the Jewel Box Cluster (NGC4755). This picture includes only part of this 10 arc minute wide spendour, showing some colour variation which gave it its name. A 20 sec exposure revealed a number of fainter stars down to about magnitude 17 or 18. Again, to get an idea of the scale, the distance between the two brightest stars is 39 arc seconds.
(Note, these are all raw images with no image processing done to them at all.)
