Auito focus and infra-red.

[John Hill]

My Pentax *istDS is a great camera but sometimes the auto focus just does not cut the mustard in the time available.  If I mount my auto flash  (Cosmos 35AF) it does seem to zero in much quicker presumably because of the infra-red beam from the flash unit (?).

So the question is,  "Would some kind of camera mounted infra-red focused beam help the auto focus?"  I am particulary interested in those low light conditions where actual flash is a no-no.

[apocaplops]

Hmm, I know Polaroid used to use a Sonar autofocus - not that it helps your situation. I would think that an IR beam would probably aid autofocus. A lot of night vision equipment projects IR beams to illuminate its path, I don't see how this would be any different.

Sounds like time for an experiment!

[John Hill]

I have been looking around since my post and there certainly does seem to be plenty of scope for this including IR penlights.  Maybe my pocket money can buy something...

[ImageMaker]

Some folks have been known to use a high powered penlight to project a spot of light to give their autofocus camera something to focus on.  Personally, if it's that dim, I'll be using the penlight to read the scale on the lens (even if it's an SLR), because I won't be able to see the viewfinder and I don't use autofocus much.

BTW, most of the inexpensive autofocus cameras use what amounts to a rangefinder; there's an IR beam that swings as the lens focuses, and when the sensor sees the beam, focusing is locked (and exposure started, if the shutter button is fully depressed).  This works a little better than sonar for focusing beyond a window, but still won't focus past a screen (been there, done that).