u/Complete_Yak_5131

I recently acquired my first night vision device (dipol d209) and i have problems with focusing. With the lens fully in, i have focus from about one meter to infinity, but everything closer is really blurry. When i adjust it slightly, i have focus up to 1.5 meters and everything further is a bit blurry. However when i put on a cover with a hole in it, i have focus for every range without adjusting. Is this a normal thing, or is something wrong with my unit?