What's That Little Red Dot on my Lens?

If you look closely at many old lenses you'll see a red dot. No- your lens wasn't made in India and that is NOT a bindi, nor is it a manufacturing defect. The red dot is the adjustment for focusing with Infrared film.

The red dot will be found on many lenses from the film era. If your lens does have this feature it will be found on the hyperfocal DOF scale, slightly to the left of the center line. So if you were using infrared sensitive film, you'd focus normally, then move the focusing measure to match the red dot.

Humans and normal film cannot see infrared light, so we can't focus correctly.

Now you know!

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