Webcam modifications

In the past 10 years there have been many models of webcams feasibly to be modified for long exposure.
Here you can see a list of modifiable webcams for astrophotography, but now the only one easy to get is the Philips SPC900 and eventually some second-hand Philips Toucam or Vesta (the Vesta or Toucam should be of the models with CCD sensor, not the ones with CMOS sensor).
Philips Vesta or Toucam modification
The original design of this modification can be seen at Steve Chambers's site, but more detailed descriptions can be found at Sylvain Weiler's site and Keith Willey's site.
Another very detailed site in Spanish is Espacio Profundo.
The basic modification, SC1, lets you take long exposure photos.
This modification is very delicate, since you have to disconnect small chip legs from the PCB and weld wires on them.
Philips SPC900 modification
It is also based in Steve Chambers's design, there is a detailed description of this modification at Matthias Meijer's site.
Other very detailed sites in Spanish are Astro San Justo and Espacio Profundo.
This modification is much easier than that of Vesta and Toucam, as all connections are made on a socket that connects both PCBs and it does not require welding on chip legs.
Amplifier turn off modification
It is possible to take a further step and reach SC1.5 modification to shut down CCD amplifier during the exposure, avoiding the background brightness that it produces.
This can be made with Steve Chambers's original design, disconnecting ground from the amplifier (see detail at Willie Koorst's site) , or lowering the amplifier source voltage using a zener diode (see design at Martin Burri's site). A variant that corrects the reduction of dynamic range can be seen at Tom How's site.
For SPC900 a detailed zener diode modification can be seen at Paul Hardwick's site or Julian Palmer's site. For this camera original Steve Chambers's amp-OFF circuit does not work, I have experienced this myself.
Both amp-off modifications need a CCD leg to be cut and to weld on it, but CCD legs are quite big making this task is easy to do.
A third amp-off modification wich doesen't need CCD legs to be cut but only doing a wire connection on Vesta PCB can be found at Greg Beeke's site, and you can see where this connection has to be made for SPC900 at Ken Hough's site .

Although these amp-off modifications introduce some "noise" in the images, they reduce "dark brightness" a lot in exposures of 30 seconds or more.
Theoretically, this brightness can be compensated with calibration, but calibration is never perfect and this brightness also decreases the available dynamic range.
In these pictures you can clearly see the improvement obtained by turning the amplifier off.

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