One of the nice things about flying gliders is the view through the canopy.
Perhaps less nice is how often you have company.
We all search for that distant flyspeck object, but my best acquisition distance for gliders and small a/c is about a mile -- and a quarter mile more often than I like.
At glider airspeeds, a quarter mile is workable, but less so for VFR transits at 120 kt.
The bigger stuff I do spot from farther away.
So my experience indicates that my vision picks up targets about the size of a fingernail at arm's length.
Always have your eye out for traffic. I've been in the initial climbout from a practice forced approach at a few hundred AGL and had to duck to avoid another a/c on a low level transit. I've also been vectored in front of a turboprop in a radar environment and gave the SLF a nice look at a glider as I got out of their way.