OzFclass

Maybe of interest.

https://www.surplusshed.com/pages/item/PL1313.html

This mob is trustworthy.

I would assume the window is polished to a flatness suitable to not degrade a spotting scope image but not sure.

Price is substantial but for what it is quite cheap.

Peter Smith.

what would you use it for ????????

If you were using a high quality scope in a very hard environment where a lot of grit was blowing onto the objective, it would be ideal.

Probably not a lot of use for most rifle shooters but protecting some optical gear in harsh environments it would be very useful. Like on robot sensors that have to operate in windy gritty areas and be cleaned regularly without scratching.