In its original setup, this is your standard high spec telescopic sight, but it's been fitted with some auxiliary software and hardware, which adds the following functions:
Range Finder Allows you to accurately measure distances up to 200m, displayed on the actual unit and in the reticle. Practical use for this is dubious at best considering that bullets in Payday 2 use hitscan mechanics and have no simulated gravity or windage effects. Furthermore, very few in game locations exist where targets can be engaged from even remotely close to 200 meters away. However, it can be extremely helpful in obtaining the Far, Far Away achievement, as it makes identifying enemies that are at 40m or further much easier.
Auto-Tagger In stealth, the scope will automatically tag any enemy you sweep your sights over, and once the alarm has been sounded, it'll auto-tag specials. This acts similarly to the effects of High Value Target Aced, and having the skill will also cause the increased damage and mark duration.
Note: Due to a bug in the current version of the game, this scope is unable to mark enemies in stealth. This is not intended.
The Theia Magnified Scope's in-game optic is extremely simplified compared to the real BORS. The system, when paired with a magnification scope, would show indications of humidity, environmental temperature, barometric pressure and projectile elevation/depression for precise compensation, which the in-game scope lacks, though seeing as every sniper rifle in the game uses a hitscan system to determine shot placement, the other miscellaneous functionalities are likely not needed.
When aiming down the sight, there is a dim "Y" above the "M" that stands for meters. This dimmed letter would stand for Yards, a different unit of distance measurement. Since the game only uses the metric system, the reason for this being there isn't exactly clear.
The Theia Magnified Scope currently has the largest magnification in the game.
In Greek mythology, Theia was the Titan goddess of sight and shining light of the clear blue sky.
The method of obtaining the sight is ironic to an almost bizarre degree as it's intended for precision shots at long range and not for something that in reality would be haphazard to the point of being insane (i.e. Zip-line Rifling).