Re: focus

[glsmyth@xxxxxxx]

From:           	Llamapix@xxxxxxx
Date sent:      	Sat, 8 May 1999 13:43:29 EDT
Subject:        	focus
To:             	infrared@xxxxx
Send reply to:  	infrared@xxxxx

> I have been shooting portraits with IR.  At first I shot some semi low-light 
> pictures using larger apertures like f/3.5  In spite of careful focusing and 
> offsetting to the IR mark, it seemed the subjects' faces were slightly out of 
> focus.  I then theorized that perhaps since the film was being exposed by 
> both visible and infrared light, that by using the offset focus I was 
> therefore leaving all the visible light rays out of focus.  Is this the case?

Yes.  The smaller your aperture, the fewer problems you'll have 
with this.  I generally shoot f16-f22, so I never see this.

Additionally, if you are using a zoom lens, the IR mark may only 
refer to the shorter focal length.

george


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