Shortly after the release of the famed Orange Box, Valve embarked upon a series of "Directed Design Experiments" that Gabe Newell hoped would spark a new wave of creativity at the studio. One of them, as explained by the Half-Life Wiki, was called F-Stop, and it was enough of an internal hit that it was tapped for full development as a prequel to Portal. For reasons unknown, that prequel never came to be, and the whole thing sunk into obscurity—another Valve mystery, to be occasionally whispered about in Reddit threads.

One of the reasons so little is known about F-Stop is that Valve simply refused to talk about it, apparently out of hope that it would actually turn it into a proper game someday [Half-Life: Alyx stares directly into the camera]. Valve seems to have had a recent change of heart, however, as an upcoming YouTube series called Exposure, being made by indie studio LunchHouse Software, will not just explain how F-Stop was intended to work, but actually show it in action.

"The mechanics are not based on speculation or hearsay. Instead, Exposure uses the original, official code from Valve's own F-STOP, or as it was properly named, Aperture Camera," the video description states. It also notes that Valve has given the studio "explicit permission to continue with our project using their original code."

The "gameplay" in the clip bears more than a passing resemblance to Superliminal, a perception-bending first-person puzzler released in November—a similarity that didn't go unnoticed on Twitter. That may be why Valve is suddenly willing to let this cat out of the bag: There's not much point in keeping your special mechanic a secret if someone else has already turned it into a game, after all.

So F-Stop by Valve?October 23, 2019

And while an unused game mechanic might seem like a thin basis for a multipart video series, LunchHouse's Tristan Halcomb told USgamer that there's enough to it to make more than a dozen videos, although they're aiming to keep it to five or six.

A full release schedule hasn't been set yet: Halcomb said LunchHouse wants to "discuss the future of the project a bit more with Valve to see what opportunities we may have going forward before committing to a follow up, so we're working based on their schedule to some extent." For now, you can follow along with the project at exposure.lunchhouse.software.