A major pain point of dew-heaters is if they are too strong, they induce "tube currents". E.g. the heat from the dew-heater causes the air around the heater to start convecting, which causes ripples in the final image. It's not really visible as ripples, but a general blurring of the image. It's essentially recreating astronomical seeing conditions inside the telescope itself, which is obviously not ideal :)
I think some fancier setups will be "active" and regulate themselves based on ambient temperature, but it's a lot more common for people to over-build their heaters and then use a dimmer switch. So you make your dew-heater for the worst winter night you expect, then dim it down for the rest of the year manually.
A major pain point of dew-heaters is if they are too strong, they induce "tube currents". E.g. the heat from the dew-heater causes the air around the heater to start convecting, which causes ripples in the final image. It's not really visible as ripples, but a general blurring of the image. It's essentially recreating astronomical seeing conditions inside the telescope itself, which is obviously not ideal :)
I think some fancier setups will be "active" and regulate themselves based on ambient temperature, but it's a lot more common for people to over-build their heaters and then use a dimmer switch. So you make your dew-heater for the worst winter night you expect, then dim it down for the rest of the year manually.