Dew Problems

[Starwiz]

The humidity in Malta can be quite high, especially when there's not much wind.

The dew problems started quite early last night and this is a frame from around midnight after I'd been imaging for about 90 minutes.  I've stretched it to highlight the problem.

The primary looked OK this morning, although everything else including the towel I leave over my laptop was pretty damp, so I'm trying to figure out if this is dew on the secondary, the filters, or on the sensor.

The air temperature was about 22 deg C.

I'm using a home-made dew shield, but would a dew heater help under these conditions?  I'm thinking if it's dew on the sensor, then it probably won't help?

I don't want to start looking for it as I'm in the middle of an imaging project, so want to keep my camera position precise.

John

[runway77]

I recommend to use a fan set to minimum while taking photos and a dew heater that wraps around the stalk of the secondary mirror holder. The heating power need to be set only to such a level that the temperature of the mirror won't fall under the dew point.

[Starwiz]

1 hour ago, runway77 said:

I recommend to use a fan set to minimum while taking photos and a dew heater that wraps around the stalk of the secondary mirror holder. The heating power need to be set only to such a level that the temperature of the mirror won't fall under the dew point.

Thanks.

John