On the rangefinders that you see from the top of Stug's and other AFV's why do some have long barrels or covers on them and some don't? What did these covers do? When should I put these on my models?

I think you mean the scissor periscopes sometimes seen in kitform on tripods mounted clear of vehicles . They will triangulate but only short range distances . The long tubes over the optic lenses are used where ever glare from snow , water , even refraction from sand (the mirage which fools people into believing they see water ) are evident , they help to narrow the field of view . Take care

Thanks! That is what I thought! I just couldn't find anything that was concrete! So do you think that they wouldn't be accurate on vehicles around the D-Day time frame?

Not really used in that time frame no . More in western desert , Eastern front winter or maybe a coastal defence battery scenario . Not by armour in normandy . Hope this helps .

Not really used in that time frame no . More in western desert , Eastern front winter or maybe a coastal defence battery scenario . Not by armour in normandy . Hope this helps .