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There is actually a formula for dew shield length, i think it is 1.5x the tube dia, but that could be wrong. I have made them out of thin yoga mats cut to suit and duct taped on the seam, works fine, use black foam, you can order them online very cheap. If you have an old hikers matt that will work as well. You can buy proper Farpoint ones from Bintel $$$.
Secondary heaters are more complicated, check them out at Kendrick Astro online to learn which one might suit you best.
You can usually still get some light through when fogged up but it does look like looking through fog - sort of like your image.
Hair dryers can work but i always consider them abit dangerous when your holding an AC powered device on wet ground, in an observatory no risk but you have to keep checking to see if you need to do it again.
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