Horizon Forbidden West - All Signal Towers (Signal Lens) Guide

You can gather all signal lens even without initiating the corresponding quest, and just trade the lens for rewards after you do complete it. It's good that you start sooner as it maps the locations of all towers, so it's easier to find them.

To start the quest, you must have first completed the 3rd story quest "To the Brink". Go a bit to the north of Barren Light where the green questionmark is displayed on the map. Talk to Maleev to initiate the quest and make your way to the top where you will find Oseram on the cliffs and some machines. Get rid of the machines, talk to Oseram and climb the nearby tower to gather Lens of Evening. Afterwards, you can find Oseram in Barren Light near the campfire and you can trade lens for rewards.

The only lens that are blocked are Lens of Afternoon for which you will need to do the The Twilight Path quest.

0:01 - Signals of the Sun Quest & 6:35 - Signal Tower #01 (Lens of Evening)
9:31 - Signal Tower #02 (Lens of Dawn)
12:27 - Signal Tower #03 (Lens of Morning)
15:11 - Signal Tower #04 (Lens of Midday)
18:44 - Signal Tower #05 (22:25 - Lens of Afternoon)
24:49 - Signal Tower #06 (Lens of Twilight)
27:01 - Exchange Lens for Rewards

Lens of Evening & Signals of the Sun Quest

Finish Signals of the Sun Quest where you will have to climb the nearby tower, on top of which you can find this lens.

Lens of Dawn

Northeastern part of the map, a bit north from where you start after the prologue. 

Lens of Morning

Northwest from the first settlement Chainscrape, on northeastern part of the map. 

Lens of Midday

East from the first settlement Chainscrape, on northeastern part of the map. 

Lens of Afternoon

First, start "The Twilight Path" Quest given by Petra in Chainscrape. To start the quest, you must have first completed the 3rd story quest "To the Brink". Without this quest you can't really reach the top of the hill where this lens are. When you approach the quest point on the map, destroy the machines. You now have to reach Savorah further uphill, and you now must reach the top of the nearby tower where you can find item to progress the quest further, and the lens are just next to the item (the item is Stormbird Heart).

When you gather all lens, meet Oseram in Barren Light near the campfire and trade lens for rewards and to finish this questline.

Lens of Twilight

Far east from the Barren Light settlement, on the top of the hill.