In the past couple years, my ST-6303 has degraded such that it takes about an hour after reaching -35C for the flats to stabilize. Before reaching steady state, the images show an expanding, racetrack-shaped acceptable area surrounded by noise. I have been told here that this is frost, and the desiccant plug needed to be recharged. Yesterday, I followed the directions in the manual to a tee, after reading Colin's helpful reply. Attached is an illustration of how the flats appeared. The cooler was set to -35C. Ambient temperature was less than 15C, and humidity below 20%. Flats were taken with an electroluminescent panel. Ignore the nearly opaque defect at top center. The nine panels in the image show the appearance of the flat frames vs. time after reaching the temperature setpoint. Those are hours and minutes. It took nearly a half day to reach an acceptable state. I have never seen anything like the first 1 1/2 hours. The pattern at 2 hours and 7 minutes became familiar, but the evolution of the clear area is slower than ever. Should I expect this recharged desiccant plug performance to improve in coming days? If not, is a new plug available? And if that's not it, perhaps the camera needs to be sent in for servicing. I have a couple high-priority targets to image in the next couple weeks, so my plan is to leave the cooler at the setpoint, which won't tax the camera in my air-conditioned observatory. Any help you can provide would be appreciated. Tom
It takes about 24 hours for the humidity to be extracted from the chamber. If it's very wet in there you may have to recharge the desiccant twice. It is best to keep moisture out of the chamber altogether, so we recommend recharging every two years. In very humid environments we recommend doing it every year. This prevents contamination and eliminates any potential of corrosion of the electronics in the chamber.
Okay, thanks, Doug. Do you thing that it's currently much worse than before the bake due to the transient drying of the chamber? Tom
Normally the humidity in the chamber is under 3%, and with the sensor at -35C it needs to be that low. So even if you had 20% humidity the chamber was flooded with "moist" air while you refreshed it. I should also comment... while you let the desiccant do its job, DO NOT turn on the cooler. It will be competing with the desiccant for pulling moisture out of the air, slowing down the process.
Okay, that makes sense. Regarding your comment about not turning on the cooler during the 24 hours that the desiccant is doing its job, that would be a good thing to add to the manual. Since I do photometry, I want to use the camera on every clear night, and was just raring to go with turning the cooler right back on.
