Hemi,
Being in Darwin, you've seen how the windows of air conditioned places fog up during the wet - that's what dew looks like. And the effect of looking through a fogged up scope is the same as looking through a fogged up window - crap,
Many factors affect the formation of dew, not just the 'dew point'. The lay of the land for one. If you are set up on lush turf/agricultural land, dew forms more readily as there will be more moisture released into the air from the soil and turf. The topography - a valley will fog up, but the ridges of the valley will remain clear. Wind will prevent dew from forming, and dry it off too if it has formed on a surface.
Alex.