Focal point and relay device
When working on their teleportation technology, the Black Mesa science team discovered that the alien world Xen was somehow involved during the teleportation process. This unknown factor had previously prevented them from accurately predicting where any teleport event would lead to back on Earth.
To counter this, they discovered they could build a device which attached to the realm's strange crystalline structures which allowed them to create a focal point and relay that aided in the teleportation. A survey team was sent to the borderworld to set up the machine, but the scientists lost contact with them shortly after it was put in place. The scientists later discovered other methods of aiming the field and abandoned the device.
In appearance, the Focuser is a large machine with two rotating arms known as emitters attached to a large crystal. It is powered by a small portable generator. The arms are controlled from a console nearby which must be aligned to achieve a maximum strength signal to the teleportation equipment in Black Mesa. When the device is tuned, the affixed crystals begin to glow.
In Blue Shift, Barney Calhoun and his associates need to make use of the old teleporter equipment in the Section A-17 Prototype Labs in a plan to escape the facility, but the equipment does not have the ability to target an Earth destination in its current state. Barney is sent to Xen to find and activate the Focuser to fulfill their plan. Once he finds the device, he has to power it on and manually align the emitters. When it’s fully activated, aliens start to appear and attempt to stop him from returning to Earth.
 Behind the scenes
In the Half-Life storyline, series writer Marc Laidlaw intended for the satellite featured in the original game to play a larger role. It was to be part of an array with three sections. He stated that one part of the array was in the Lambda core, one was in Earth's orbit as a result of the launched delivery rocket, and one was in Xen. The Focuser featured here in Blue Shift is said to be the Xen part of the array.
 List of appearances
- Half-Life: Blue Shift (First appearance)