Focusing Leica lenses with infrared film

[tbm]

I would truly like to finally shoot some b&w infrared film with my Leica M and R lenses, but none of them have a marking for focusing. Does anybody have a foolproof method for accurately focusing said lenses?

Terry

[Ole]

It would all depend on the lens. There are unfortunately no absolute rules for how much to shift focus with IR film.

However: Unless you use Kodak HIE it doesn't matter. All other films are only sensitive to near-infrared down to about 800nm, which is close enough to visible light that most lenses will be fairly wll corrected. I've shot the new MACO IR 820/400 with a Voigländer 21mm lens, nd everything was tack sharp. Of course the extreme DOF with a 21mm lens helped a lot

[mono]

As far as I know Leica lenses need no correction with IR! That is why you`ll find no IR marks on them.

[Claire Senft]

I have no experience with infra-red film...zero. I am thinking about Ole,s remark inre: the 21mm Voigtlander. He states that the exreme depth of field helped a lot.

I wonder if this is so. If the focus shift happens at the film plane..depth of focus..then the shorter the focal length the more of a problem you would have. Stopping down of course would help.

[Woolliscroft]

Stop down a bit and the DOF should get you through. It works for me.

David.

[Ole]

.. the exreme depth of field helped a lot.

I wonder if this is so.

Since I used a Bessa-L (no rangefinder), all my distances were guesstimated. So DoF was a really great help!

Any difference in focal plane between IR and visible light should be less than the thickness of the emulsion from what I have seen of data on the 21mm Color-Skopar.

[JohnArs]

Mono is right on!
The quality of Leica lenses is up to the IR span and so they need no correction.
So don't worry be happy!

[Lee Shively]

I've had limited experience with IR films but the biggest obstacle was using the dark red filters, not the focus compensation. Stop down a bit and you won't have any problems. Leicas--all rangefinders--overcome the problems of using dark filters since you don't have to focus through the lens.

[Helen B]

I'm not so sure that Leica lenses are corrected into the infrared. Remember that an IR focus mark only applies to one wavelength, probably at one distance setting. With IR film you have a choice of filter and film combinations that result in different centre wavelengths. If you are focussing by eye, rather than by scale, through a red filter then the focus point may already be affected by wavelength.

I have read sources on the internet (Willem-Jan Markerink is one) that say that Leica do not put IR marks on their lenses nowadays because they could give a false sense of accuracy. Whether that is true or not, I share the view that the answer is to stop down.

Best,
Helen

[Trivette]

I'm not so sure that Leica lenses are corrected into the infrared.....

I'm not sure either. The 40mm Minolta M-Rokkor has a focussing mark for IR, and it is optically identical to the 40mm Summicron-C.