I can't tell if the grain is from the rain or not.
That camera (the Z12) has issues with keeping focus during the Day/Night switch, particularly over 80% zoom. It helps if you can have the switch occur while there's still enough light for it to find something to focus on.
BTW, if it matters, the first set of turn arrows per IPVM calc are 220 feet away.I think you could zoom in a little more and go further down the road where the "pinch point" is smaller and maybe get bigger plate image and still have all three lanes? Maybe the center of the image be those first set of turn arrows?
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Post your video settings. Lets see what you have going on. I think you need a darker image (e.g. faster shutter speed). Below is one of mine from last night. See how dark it is. @bigredfish 's images are even darker if you look at some of his previous posts.
No, my captures aren't that grainy. I also have my IR at manual at 100%.
Also what are your daytime settings?So 1/2000 should be good. Are you you using a fixed shutter or a range? I also use "Manual" and not shutter priority but I'm not sure if that makes a difference. Here are some of my setting for comparison.
What about your actual video settings? Codec? Bit rate? etc...