RE: Autofocus lenses for IR?

[Rolland Elliott <rolland_elliott@xxxxxxxxx>]

Andrew Davidhazy ANDPPH@xxxxxxxxxxxxxxxxxx wrote:

<<<<Subject: Re: Autofocus lenses for IR?
My tests indicated that at least some cameras could indeed focus
infrared at least adequately and when there was lots of it.I used a
Sigma AF camera and a Canon Elan and covered the lens with a 87
filter...and noted where the focus ring would turn when aiming at a
far awaysubject. In both cases the lenses "racked out" vs. their light
focus setting.>>>>

There is one big problem with the above method:  You can't compose
your picture through the viewfinder of an SLR Auto Focus camera with
an opaque filter over it.  

The method previously posted (and the one I recommend) suggests using
a thin 87 or 87C gel over the AF sensors (usually located at the
bottom of the mirror box) inside of the camera body, AND a thin gel
between the filter rails.  This has two benefits 1) AF focusing in the
IR region and 2) dramatic IR images using the sharper cutoff of the 87
and 87C opaque IR filters, while still maintaining through the lens
viewing.

Of course you needs lots of IR light present or autofocus will not
work.  
I'm sure one of the reasons no one sees lots of action  IR images with
shallow depth of field is because of the inherent problems of focusing
IR light accurately and quickly with the shallow depth of field
associated with long telephoto lenses usually used for action
photography.

The above method should solve these problems quickly and easily.

Try it and report your results back to the list.

Peace Rolland 






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