Even a magnifying glass isn't going to burn things by just holding it in the light. You have to angle it and move it further/closer to actually focus it all into a tiny little pin-sized area. Average prescription lenses not being as powerful lens wise as a magnifying glass would require even more playing around with to focus the light into a small enough point to actually start a fire.

[–] Dalvoron@lemmy.zip 1 points 2 weeks ago (1 children)

Right, but we're talking about the eye, which glasses are made to focus light into a pin-point with in combination with the natural refractive properties of the eye itself when placed at a specified distance from the eye. Naturally if the glasses were specifically created with a more appropriate focal length, it would be much easier to start a fire with them.

[–] Kolanaki@pawb.social 2 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

They focus into your retina, which is small, but not pinhead small. The length they sit away fron your eyes is part of it. You could take them off and get that focal point to be concentrated in much smaller area.

[–] Dalvoron@lemmy.zip 1 points 2 weeks ago

The retina is not as small as a pinhead, but the light from any source doesn't get focused over the whole thing, it gets focused to a point. Anything else would mean the image is blurred, defeating the point of the glasses.