Taking a completely uneducated look at the photo from someone who knows nothing about tanks(!)... The two white dots could be a reflection of a lens or prism slightly set back from the aperture. Then if you stare at it for long enough the apertures could actually be convex, either covers or again, some sort of lens. Also, to the lower right of the turret there appears to be a large plate with 6 big rivets in it which looks like it would interfere with turret rotation. Sorry, that's the best I can offer.