Thinking about optics and what can go wrong, in the context of making decisions about BUIS.
I realized that I have often had a problem with the simplest of optics: sunglasses. Here in SE TX, on a lot of days, if I put on sunglasses in the air conditioned office, or have them on in the car, and step outside, they immediately fog up for at least 20-30 seconds. It seems that this is a likely, perhaps the most likely failure mode I can expect to encounter in use of a defensive optic-equipped arm in this environment. And due to the greater thickness (thermal mass) and the fact that air is only circulating on one side of the lens, a firearm optic (scope or closed-emitter dot) is likely to take longer to unfog.
Fogged glass on two ends of the optic will render a cowitnessed front sight useless, regardless of the rear sight. So it seems that if this swamp-arse humidity fogging is the concern, the lower-1/3 vs absolute cowitness argument is missing the point. If one is stepping outside and needing to shoot something, one more than likely really needs at least the ability to shoot that thing NOW. And the only solution to bridge between stepping into the humidity and the lenses warming up and unfogging themselves is offset sights (or just dedicate the gun to irons).
I haven't actually experienced this fogging with a rifle optic yet, but I know there are a lot of carbine users around here and throughout the Swampy South. Am I larping my way into a non-situation? Or is this actually a thing that pro users deal with? I'm reckoning more than one person here has had a carbine in a vehicle with A/C and stepped out into the humidity needing to use it right away. Would like to hear some input from the voice of experience.
@Rex G @SouthNarc @Wayne Dobbs @HCM @Chuck Whitlock @LSP552 @HCountyGuy