infrared focussing shift on bronica ec-tl with 50mm nikkor

<p>Question is about refocusing for IR film (I will use maco/fotokemika IR film) on old Bronica

with old Nikkor (EC-TL with 50-H).<br>

I know I will have to shift measured focus a "little bit" closer, but I don't know how much or how

little. Anyone have tried IR on old Bronica?<br>

The problem (as I see it now) is that people are talking about setting measured focus on "right

hand" f5.6 mark. that will be "left hand" (closer) on my Bronica. My Bronica have marks for

75/80/100mm lenses, but non for 50... o.k., that isn't a big problem if I have to shift, let say

10meters focused to 8m, but what if I have to shift from 2m back to 1.5?</p>

<p>Tnx, Janko.</p>

First off, I don't think the shift is as drastic as 2m to 1.5 or 10 to 8.

The actual shift will depend on the lens construction. Supposedly, some well-corrected lenses require no shift at all. Using a filter/ film combination that is closer to visible light, or a mixture of visible light and infrared, requires less shift or no shift.

With a red #25 filter, I suggest focus and stop well down. With a wide-angle lens, depth of field should be adequate to allow for any minor focusing errors. Even with the opague filters, it shouldn't be that critical.

From the Kodak website, I find this (discussing focusing with HIE):

For best definition, make all exposures at the smallest lens opening that conditions permit. If you must use large apertures and the lens has no auxiliary infrared focusing mark, establish a focus setting by trial and error. Try extending the lens by 0.25 percent of its focal length beyond the correct focus for visible light. For example, a 200 mm lens would require a 0.50 mm extension as 200 mm x 0.0025 = 0.50 mm.