Where I live, I have at least 4 street lights visible from my two observing spots; both LED and Sodium Vapor. When using the 1x Envis on my Mod 3C, I always held my free hand close to the Envis lens to block stray light that would hit the lens and cause glare. So I decided to make a shield to extend in front of the lens.
I used bathroom sink drain tubing that is chromed brass. The outside diameter is 1-1/2"... the inside is slightly over 1-7/16". In any event, it must fit over the Envis lens. The tube I used is a PERFECT fit over the Envis lens, with enough friction to keep it securely in place.
I started out making it 2.25" long and then shortened it in 1/8" increments until vignetting disappeared from the FoV. The final length became 1-3/4" which allows for 7/16" of shielding beyond the lens. I tried painting the inside with flat black, but glare was still present, so I cut a 3/8" wide strip of sticky back felt and put it on the inside of the tube... it really did the trick.
I've used it 3 nights now, and find it to be pretty effective. It allows me to scan the sky within about 5° of the sodium vapor lights (and the moon) or, within 10° of the LED lights without excessive glare on the lens. If you live around lots of streetlights, this is a pretty effective and inexpensive aid.
Now, I can use my free hand to shield the ocular and my eye from all those streetlights!