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Hi Chris, having had SCTs and maks for years the solutions are:
1. Fan, moving the air. Alternatively set up the scope where there is a slight breeze - this will also keep the dew off.
2. A 12V hairdryer will blow warm air to remove dew and also warm the corrector enough to keep it clear for an hour or two; you can find these on eBay. Simple and effective.
3. Heating the OTA as previously with heater straps and battery;
4. Adding a dew cap - a long lightweight tube extending forward from the scope typically 1.5X the aperture, these are usually made of foam rubber or plastic and slip over the OTA. The stuff used for yoga mats works well. This helps keep dew off (it is formed by sinking air).
5. Keep the scope indoors (and warmer than the night air). While observing, wrap the OTA with a very good insulating material - ideally Reflectix - to minimise the heat lost from the OTA.
6. Repaint the OTA white. The dark blue and black colours which Meade and Celestron used are about the worst possible choice because they cause the scope to radiate heat away quickly which is counter productive.
Regarding point 6 the internal air current (“plume”) frequently seen in SCTs and maks is a result of the thermal gradient between the warm air inside the scope and the outside air. Reducing the gradient will stop it and this can be achieved 2 ways - either cool the scope quickly (but the corrector will fog) OR insulate the OTA to stop the heat loss.
7. Regarding heater straps, these are most effective if used to warm the barrel of the OTA and this is in turn wrapped with some form of insulation - which could be a dewcap.
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