The bottom optic in that photo is an AN/PVS-4 Night Vision Sight.
The PVS-4 is a 3.6x scope, usually Generation 2 but there are Generation 3 PVS-4 scopes out there. While considered obsolete in the U.S. the PVS-4 still gets used around the world.
This scope is sizable, 4 pounds and over a foot long.
The PVS-4 comes with a mount that can be attached directly to an AR15/M16 Carry Handle. A variety of other mounts, including the pictured rail grabber are also available. The PVS-4 also has a variety of mounting options for grenade launchers and crew served machine guns.
Operation is pretty simple, everything is clearly labeled.
The PVS-4 originally used a weird battery (BA-5367/U) generally unavailable anywhere. Adaptors exist allowing you to use 2 AA or 1 CR123 batteries instead. Many PVS-4 scopes have two places, on the top and on the right side, where you could install a battery. Only one battery is needed to use the optic. These scopes have been made by many companies in many places in the world, some have omitted the side battery compartment, others were built or rebuilt to only use 2 AA or 1 CR123 batteries.
The AA battery adaptor shown above can only be mounted on the top of the scope, the CR123 adaptor shown below can use either mount.
The objective lens cap for the PVS-4 gives you 6 different options for varying the amount of light let in. This lets you use the scope during the day, even during the brightest day in the deserts.
The downside is that your view through the scope becomes somewhat obstructed. I’ve read that people saying they had zero shifts from zeroing with the cap on then shooting with the cap, but I haven’t had the chance to test that.
Reticles are interchangeable if you can find the relevant reticle cell. The one pictured above is the M16-M203-M79 reticle. Other options include a cross hair, M14-M60, M2 Heavy Machine Gun, and some assorted rocket and missile launcher sights.
Unfortunately due to the combination of the illuminated reticle, tube brightness, and the daylight apertures makes initially using the scope a little more complex. When I went to take some photos, I initially got the tube brightness and focus set up so I could see the target clearly but then when I turned on the illuminated reticle it was too dim to see, even at max brightness. So I had to reduce the amount of light coming in and put the reticle brightness on max to get the photo above.
The photos really don’t do the optic justice.
Much like with the Darkstar, when I tried shooting clay pigeons at 50 yards offhand I found the optic slow and awkward. It is really best employed from a stationary position and some sort of rest.
Side note, I found on this PVS-4 someone had cut out the flaps in the eye piece. Normally these eye pieces have 2 flaps to prevent light from spilling out when the optic is on. Most people find them annoying because you have to press your face into the eyepiece to be able to use the scope. Most of this style eye piece that I saw in the military had this same modification.
The PVS-4 is perhaps one of the best Gen 2 night vision optics available, and was quite popular compared to the early 3rd Gens due to how well it handles bright lights. Early 3rd Gen Nightvision would have large halos around bright lights while the 2nd Gen PVS-4 does not have that issue. That is why you may find some old recommendations where the PVS-4 is recommended for urban use over Gen 3. That said, newer Gen 3 is far superior to the PVS-4.
It is a good optic, and still works well, but there are far smaller and better options available to us now.