Fourier, thanks for confirming my worst fears - that i'm going to hate having that wide frame distorted 2.8mm lens in my
amcrest. i'd order a 4mm or 6mm already (may take a few weeks to arrive) but i want to wait till i have it in my hand disassembled before probably getting it wrong. my amcrest will be mounted between trees, so i already know too wide will waste half my field of view with wind moving branches. here are the two lenses i'm probably going to try. (i'm new at this, so nobody take my word for these working yet);
amcrest's original lens appears to be from it's specs; M12 2.8mm F1.6 5MP
4mm 5MP 1/2.5" HD IR Sensitive M12 Camera Lens | eBay M12
4mm F1.8 5MP
https://www.amazon.com/gp/product/B019S2X4JO M12
6mm F2.0 5MP
btw, i actually emailed amcrest twice (directly and thru amazon) and they do not
stock a 4.0mm lens or version of this camera even though it's available in the specs,
ICIP-B8310-IR
and seems to be resold at 4mm in a white casing by yet another dahua oem
(yes, i know icrealtime keeps contradicting itself - clueless oem proofreading)