In article ,
Whiskers wrote:

[1] Some lenses have an IR focus index as well as the visible-light one;
after focusing visually, move the focusing ring so that the distance next
to the usual focus index is next to the IR one instead. If there isn't an
IR index, use the 'closer' depth of field indicator for f/5.6. Of course
with an auto-focus-only or fixed-focus compact camera, you're stuck with
what the camera does, which will be 'wrong' - but the large 'depth of
field' that goes with a tiny sensor might offset the problem somewhat.

it depends on the camera. a compact digicam which focuses off the
sensor itself won't be 'wrong' if there's a bandpass filter in the
optical path.