The Mysterious Signal Lenses are collectibles that Aloy can start collecting after reaching the Barrier. Traveling around the area, she rescues Rayna, a peasant woman who needs all six lenses. Hunting them is part of one of the early side quests in Horizon Forbidden West called Reflections of the Sun.
Rayna explains that the towers that contain the Signal Lenses were once built by her father, but now the Carja want to destroy them due to old age. By bringing all six lenses to Raina, Aloy will be rewarded with Metal Shards, Green Glitter Fragments, and a few Ingots, valuable acquisitions at this point in the game.
Although you will have to spend some time on the Reflections of the Sun, the quest is worth taking on when the opportunity arises: thanks to it, you can already get hold of a good amount of resources at the beginning of the game, which will come in handy as you progress further.
All signal lenses from the quest Reflections of the Sun
The tower containing the Lens of Noon is located east of the Mountain Grinder just across the river. The building can be seen from the city center, it will not be difficult to recognize it. It makes sense to take this lens first even before taking the quest, because, firstly, it is easy to find, and secondly, using its example, you will understand what to look for when searching for the remaining lenses.
Lens of Dawn
The Lens of Dawn is located in the far corner of the map in the northeast. To get to it, you will need to go back the same way that you came to the Barrier after completing the tutorial.
Look for the Lens of Morning on a tower to the northeast of Gnawing Mountain, turning north from the main road that will take you to the settlement for the first time.
The Lens of the Eclipse is located south of the ruins with the Barrier relics, almost at the very edge of the map.
Lens of the Day
For the Lens of Day, head southwest of Grinding Mountain. Its location overlooks a group of Lentohorns that will always roam south of the settlement. You can get there during the course of the side quest “The Twilight Path”, to get it, talk to Petra in the bar in the Mountain Grinder. Unlike the rest of the Signal Lenses, this one is not attached to a large wooden structure, but lies alone among some ruins.
The Evening Lens is located north of Wasteland Light. To get to the device, Aloy will first need to clear a path with a grappling hook. This is the place where you meet Rayna and take the quest from her, which you can turn in there if you already have the rest of the lenses. But if not, then when you get them, look for her in the Light of the Wasteland to get a reward.
A source: gameranx.com