Charging desiccant on ST7

Desiccant

I usually recharge the desiccant about once a year and have found this sufficient. One year I forgot to do it and about six months later I noticed a change with the images I had taken. The back ground did not seem as flat and uniform as they had been and the flat fields seemed totally different from previous flats. I could not see any problems on the glass lens cover and it seemed quite clean and I was afraid the camera would have to go back to be prepared. I then recharged the desiccant and everything was back to normal.
Other symptoms are frosting on the camera glass which can look like dark doughnuts on the images and flats.

To recharge the desiccant.

Unscrew the brass desiccant container on the back of the camera. It looks like a big brass colored screw, you cant mistake it for anything else. Take off the rubber 'O' ring and put it somewhere safe.

Plug the hole with with the plastic plug that came with the camera. Finger tight is sufficient. The camera is exposed to the atmosphere while there is nothing in the hole so plug this hole as quickly as possible.

Pre heat an oven to 350°F / 175°C. I use an electronic oven temperature gauge to check this temperature as the solder on the brass desiccant container melts at about 460°F. Don't forget that ovens with no fans in have hot spots so the temperature can vary dramatically in these type of ovens.

Put the brass desiccant container in the oven for 4 hours. Then remove and let it cool.

Replace the rubber 'O' ring carefully on the brass desiccant container and remove the plastic plug from the back of the camera. Then re-insert the brass desiccant container into the camera taking care not to over tighten it.

leave the camera for about 2 hours and then its ready for action. If you are desperate to use it straight away set the temperature to close to 0°C so no frosting is visible in the images.