Re: Auto focus lenses for IR?

["Ken Evans" <kenevans@xxxxxxxxxxxxxxx>]

>Andrew Frazer wrote:
>>
> Can any of the new AF lenses
>> from any of the major camera manufacturers compensate for IR
>> focusing?
>>

I don't know that I have any real answers here, but after following this
thread, will weigh in with a couple of observations.

First of all, I don't think most shooters of IR use this film for "action
catching" subject matter.  Almost all usual IR subject matter can (and
likely should) be done using a good tripod.  This being my personal view,
then any good quality auto-focus lens, that has both a distance scale and IR
point of focus "red dot" would work fine.

Adjusting your exposure (within limits of course) to maximize depth of field
for the subject matter, you can simply focus with the auto focus turned
on.....then turn it off, and make the necessary manual adjustment according
to the distance scale on the lens.  The problem that needs to be watched out
for is that fact that most auto focus lens makers have taken to eliminating
the distance scale and/or the IR focus point red dot adjustment, on their
less expensive lenses.

I use the Canon EF lenes, and have always made sure that each  lens that I
have purchased has had the distance scale, which we all used to expect to
find on our old manual focus lenses.

Furthermore, depending on the filter used, if focusing is unusually
difficult, with a good distance scale.....you can focus without the filter,
noting the point of focus on the distance scale, then replace the filter and
manually focus back to the indicated point of focus using the distance
scale.

Due to the optics of the lens and design of auto focus sensors, I seriously
doubt that there are any lenes that can auto focus on the precise IR focus
point, which is mostly an an educated "guess", in the best of
circumstances....even with older style manual focus lenes.

Ken Evans

*
****
*******
******************************************************
*  To remove yourself from this list, send:          *
*         UNSUBSCRIBE INFRARED                       *
*       to                                           *
*         MAJORDOMO@xxxxx                            *
*----------------------------------------------------*
*   For the IR-FAQ, IR-Gallery and heaps of links:   *
*  http://www.a1.nl/phomepag/markerink/mainpage.htm  *
******************************************************