The Red 'Infrared Correction Index' on EF Lenses - how?

Can't quite understand how to use this properly - the manual is no help.

It says to focus manually and then use the appropriate red markings.

Does that mean that say I focus (on the 24-70) on an item 3 meters away using a zoom of 50. Do I then put on the IR filter and move the 3m to correspond to the 50mm red zoom mark?

Thanks in advance,
Saqib.

Yes, exactly.

Another translation...


You're taking a picture on a beach at dusk and you don't have a flash. You have a lens with a distance scale on it; so you set it for 10'; you stand ~ 10' away and take the picture; With a decent Depth Of Field you will get a shot in decent focus(ignoring shutter speed and camera shake...)

So; knowing this is how the numbers work on the distance scale; you can apply the same thing to the red numbers. The reason for two different sets is the IR wavelength is different than the visible spectrum; so it will focus a sharp image at a different plane than the visible spectrum will.

Hope this helps..

If not; let us know.

-TD

um thanks TD, but i think i prefer Jon's explanation better