Infrared refocus on Leica RFs?

[Schafphoto]

For all you Leica RF - IR shooters... what is the infrared re-focus setting on your lenses. I had a student in one of my IR workshops with a Leica and there were no red (or any) re-focus marks on any of his 3 RF lenses from different eras and Canada and Germany.

What are the focusing conventions besides "small f stop with lots of depth of field"?

-schaf

 

[Sirius Glass]

I have two Nikon AF lenses that do not have the red mark for Infrared. After I have the focus, how much do I adjust the focus? I move the focus in the direction towards infinity, right?

 

[Lee Shively]

I've not shot a huge amount of IR film but I've never paid any attention to the refocusing marks on lenses that have them. The change of focus is so slight, you would have to be shooting at a very wide aperture to miss it.

I think I read someplace that Leitz/Leica lenses were corrected for IR focus and they don't need any refocusing. Don't take that as a fact--I'm working from an often faulty memory. Of the three Leitz lenses I have handy to check--both German and Canadian--none have the IR dot.

 

[Schafphoto]

Sometimes the infrared mark is not red, sometimes it's a diamond, and R, a dot or a curved line on push-pull zooms. The correction point is always away from the infinity mark. In other words, when your lens is at infinity, in order to refocus to IR infinity, you would move the focus ring away from the Infinity point. The easy way to remember this is that you can't move the lens the other direction (past infinity? to uber infinity??).

 

[Sirius Glass]

Sometimes the infrared mark is not red, sometimes it's a diamond, and R, a dot or a curved line on push-pull zooms. The correction point is always away from the infinity mark. In other words, when your lens is at infinity, in order to refocus to IR infinity, you would move the focus ring away from the Infinity point. The easy way to remember this is that you can't move the lens the other direction (past infinity? to uber infinity??).

Thanks for your reply. I figured out that it was away from infinity after I posted. There are no marks [dot, diamonds, ...] of any kind to show where the IR focus point is, so I will try to use f/8 or smaller opening [ yes, f/11, f/16, ... ] as long as the shutter times are not too long for hand holding. Otherwise I will use a tripod to keep a small f/stop.

Steve

 

[Ronald Moravec]

With all Leica lenses and emulsions like HIE, put infinity at 5.6 for infinity pics and for pics closer, move the distance indicated to 5.6.

As more visable light enters the image as with less IR sensitive emulsions , do not compensate so far toward 5.6. This is why the lenses are no longer marked as it varies with emulsion and filtration. Old lenses were marked 5.6 for IR.

 

[keithwms]

Bear in mind that for near-IR films (i.e. everything apart from HIE) you probably won't need to refocus unless you have a very near subject, because these films are barely sensitive into the IR. Most of the sensitivity is edge red. But anyway to be safe you can think hyperfocally and focus a bit further into the scene and stop down one stop more than you would for the hyperfocal method... usually that will cover it. If in doubt take a few shots bracketing the aperture.

Now for HIE, your sensitivity would be considerably further into the IR, where the glass dispersion becomes a much bigger issue relative to the visible focus.

One of my pet peeves about the cliches of IR photography is that people tend to stop down a lot because they think they have to. A bit of experimentation reveals that some apo or even decent ED lenses do just fine and you can in fact do limited DOF work almost as easily as with normal film. But I digress.

 

[msage]

For all you Leica RF - IR shooters... what is the infrared re-focus setting on your lenses. I had a student in one of my IR workshops with a Leica and there were no red (or any) re-focus marks on any of his 3 RF lenses from different eras and Canada and Germany.

What are the focusing conventions besides "small f stop with lots of depth of field"?

-schaf

After many years and alot of IR film (rolls and sheets), I stopped worrying about the "focus shift". My negitives and prints were sharp. Often photographers over compensate for the focus and get out of focus images. I work in a lab and it often takes a few rolls or sheets ( and alot of couching ) to get consistent results.
The only exception would be close-up photography. That is the only case I would do a focus compensate.
Michael