This handy metal thumb cap for ZWO Seestar S50 smartglasses not only protects the lens from humidity, but also prevents stray light from degrading the quality of an astrophotograph. Like a solar foil, you just slide it into the housing of the telescope. Two rubber O-rings protect against falling out.
There is a 2" filter thread inside the dewcap, into which you can (with some manual dexterity) wrap your own filter, giving you more leeway than the factory solution when using filters.
Attention! Remove the dew cap before switching off the telescope! In the parked position, the dewcap can get stuck in the mechanical head of the telescope, which can result in damage.