Just finished checking outside with both scopes. I can only check a distance of about 30 yds, because my back yard is fenced. The 3-12 is running firmware .253, and the 5-18 is running .248. The 5-18 version .248, has an auto dimming feature in the firmware, and would not get any brighter than the lowest setting on the built in illuminator. It would brighten for a split second then the display would dim, on both medium and high on the illuminator. I could easily make out the nails in the fence on 5X, and see blades of grass at 30 yds.
The 3-12 with firmware .253 is not auto dimming. I could see a lawn chair and 5 gallon bucket at least 150 yds away under a security light. I could also make out the nail heads and blades of grass in my yard with the built in IR illuminator at 30 yds on the lowest setting. If I went to medium or high on the illuminator, it got much brighter. I don't think the lens size is going to be a limiting factor, but I'll hold off on that judgement until the T50 illuminator comes in and I can check them both out in a field. Hope this helps someone.