A bit about the F1G2 lens.
This is quoted as 56° field of view on this 160 x 120 12u sensor.
This gives it a focal length of just 1.8mm, which ties in with the quoted aperture and it's size.
![](https://www.eevblog.com/forum/thermal-imaging/f1g2-optical-modifications/?action=dlattach;attach=291922;image)
When considering refocusing this lens the school optics equation matters:
1/f = 1/u + 1/v (f = focal length, u = image distance, v = object distance)
If we assume it is at infinity as delivered then:
u = f = 1.8mm
If we want to come down to 50mm:
1/1.8 = 1/u + 1/50
u = 1.87mm
It only needs to move out by 0.07mm !