Focus adjustment for Infrared film

I know that using a small aperture will reduce the need for adjusting the lens to the IR focusing mark. But if I choose

to shoot at say f5.6, will the focus adjustment be any more critical when focusing at a close object, than it is at

something far away?

Dependent on the make and model of your lenses you should have an IR focus mark/setting on your lens barrel. It is usually a red line which you adjust your focus to if using IR film.

Thanks Craig, yes my lens does have the IR mark but I was asking if adjusting to this mark is more important when

focusing at a near object rather than a far one?

Well depth of field applies when using IR, visible or UV as your light source, so yes it is more important at close distances and wide open apertures.

If it's important to focus at a near object with normal film then using a film that focuses differently would logically be true as well.

 

"I was asking if adjusting to this mark is more important when focusing at a near object rather than a far one?"

 

I shot a lot of IR film and rarely used the IR focus mark. Sometimes the softness of IR is what's appealing. It wasn't important to me but if you want sharper images then it's important to you.

When I shoot IR (Kodak HIE) I use an R25 filter and just focus by eye. I have never bothered with refocussing. Mind you, having said that, I usually work at around f/11 so DOF takes care of it. And also when I shoot IR, I generally use a 28mm lens to get a more 'other worldly' effect so DOF is even greater.

Thank you all for your help.

The aperture doesn't matter assuming that you have set the IR mark and that is the DOF that you want.

 

The published information in my youth a bit over 50 years agos was that you would extend the bellows by a factor of 1/2 of 1 percent. Try to measure that if you can! That is why the helical focus can have you simply move to the little red mark.

 

Lynn