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Announcement
Improved External Dew Control for STL Cameras
January 16, 2006

Some users in very humid climates have reported external dewing on the CCD chamber window of STL-11000 cameras. This is a different phenomenon than frosting inside the CCD chamber due to moisture. The latter may be cured by recharging the desiccant plug. However, external dewing is a different problem. It results from a large CCD such as the 11000 cooling the chamber window relative to the outside air. We initially added two window heaters to sides of the CCD chamber that drew power from the TE cooler power supply. This worked in most cases to eliminate the problem. We were unable to dew the outside of the CCD chamber window in conditions below 80% humidity. However there were still reports, mostly from the UK and the East Coast of the US of dewing on the outside of the CCD chamber window when the weather was particularly humid. We have improved the original modification by (a) adding a third heater along the third available side of the CCD chamber, and (b) adding a new power harness that re-routs the power to the heaters from a supply in the camera that does not vary with the TE cooling power. The problem we found with the prior method was that when the dewing occurred, power to the TE cooler was often reduced to bring up the temperature slightly, but this also reduced the power to the heaters. The new design eliminates this problem. The new design has been tested in the UK and in the Southern US with success. We will make it available at no charge to anyone who experiences excessive dewing at normal operating temperatures with their STL camera.

As an added benefit, if you are in a warm dry climate, you may find it is better not to use the heaters at all because there is no need for them. In the current design with two heating elements running all the time, there is a small penalty in absolute cooling of approximately 2 degrees C over no heaters at all when maximum power is requested of the TE cooler. With the addition of the third heating element, this may increase by another degree, so the penalty will be a total of 2-3 degrees max cooling over no heaters at all. However, in the new design, we will make the heaters on/off switchable so you can turn them off completely if you don't need them and recover those 2-3 degrees.