Littlefoot Elegance Photo User

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Sunday, 26 August 2007

Webcam Modifications 1

The first camera that I bought was back in June 2001, a Philips Vesta Pro 680. This was recommended as a good camera for planetary imaging, being sensitive and easily adaptable for prime focus work, with a Mogg Adapter. This is a 1.25" tube that screws into the body in place of the original lens. These adapter are available at reasonable prices from Steven Mogg's Website.

In October, Steve Chambers developed a long exposure modification to the Vesta and ToUCam webcams. This coincided with Philips discontinuing the Vesta 675 and 680 camera range. For a very short time it was possible to pick up a Vest 675 for just 25 GBP. I bought one as a backup in case my 680 mod failed. With hindsight I wish I'd bought a few more! The mod to the 680 went according to plan, firstly confined to its egg case, and latterly as a Peltier cooled prototype.

Please take heed of the copyright condition associated with this modification which Steve Chambers has generously made available for persoanl use. The notice is viewable here

Peltier Cooled Prototype

Here is a brief description of my Peltier Cooled SC prototype:

Tne concept was to re-case my Vesta Pro SC in a larger case that would allow cooling of the CCD. I had an aluminium Eddystone Box, which was about the right size, and one of the QCUIAG members had found a cheap source of Peltier coolers at Greenweld . I ordered two Peltiers and after a couple of trips to Maplin Electronics, I was ready to construct a Vesta Pro SC2.

The chassis is the lid of the Eddystone box. The heatsink and fan module is a Socket 7 CPU cooler, the face of which protrudes through a slot cut in the lid. Self tappers fix the fins to the lid. The 6V Peltier is sandwiched between the heatsink and the coldfinger. The coldfinger is made from 25 mm square section aluminium, cut and bolted together. The clamp bolts are isolated from the heatsink and coldfinger using insulating sleeves. The fan and Peltier are wired out to a standard 'co-axial' power connector. The fan is permanently on, but the Peltier is switched.

Removing the CCD from its PCB was fun...two evenings worth (magnifier, soldermop and 15W fine tipped iron). Here it is shown clamped to the top of the coldfinger with self-tappers. The clamp/window was made from an off-cut from a CD case. The CCD PCB was drilled and screwed to the lid. The main PCB (not shown) is also supported from this, on its connector. I tried to keep the leads to the CCD as short as possible (~ 6 cm).

I dismantled an old Pentax fit 2x teleconverter, to give me a sound means of mounting either 35mm camera lenses or a range of T Mount telescope accessories in front of the CCD.

This picture shows the completed camera. In front of the Pentax PK bayonet mount is my home made focal reducer, made from a 8 x 35 binocular objective mounted in a 20mm M42 extension ring.

Note also, that I have adapted the tripod socket from the Vesta, for use in the modified camera.


After a cursory inspection, I plugged into the PC. All I got was a garbled noisy mess. I wasn't surprised, considering the heat I'd applied to the CCD trying to extract it! On closer inspection (of the CCD and its datasheet) I found that I'd got pins 1 - 7 of the CCD wired backwards.

After re-wiring I gave it another go and amazingly the camera worked perfectly, with no noticable patterning/dead pixels etc. The Sony CCD appears to be pretty bullet-proof.

For the tests, the Peltier PSU was a plug-in battery eliminator rated at 1A. I measured current to Peltier at 2.1 A. I later built a high capacity (25 A max) power supply, using a standard 250W Desktop PC switch mode power supply.

Under Pelteir cooling a thin layer of ice formed on the coldfinger. In use exposures in excess of 1 minute were free of hot pixels, at maximum gain.

Removing the CCD is harder than doing the basic SC Mod, but the unit can take quite a bit of abuse, as I have demonstrated.

I later added the standard Amp-Off Mod, to cut out electro-luminescence caused by the CCD's on-chip pre-amplifier. This significantly improves the performance of the camera for exposures of more than about 30 seconds, at maximum gain.

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