Infrared Focusing

[stray_227]

I'm still having focus issues with Efke 820 Aura film - both Medium and Large format. I'm making "the adjustment" - on the little red line and infinity mark on Mamiya 43mm wide angle but also on Kodak Ektar 14" 8x10.

Any thoughts or better guidelines ?

thanks

shawn

[polyglot]

Assuming your images are coming out focused too close, don't make the adjustment. The IR mark on most lenses pertains to much longer wavelengths like 1um (1000nm) that IR820 just can't see.

While there is a small focus error between 650nm (red) and 780nm (the peak sensitivity of IR820+R72), it is very small. Probably smaller than the focus difference between red and blue light with a decent lens.

[ataim]

Also make sure to stop down quite a bit. My normal work flow is to compose and focus under normal conditions, then add the ir720 filter. With it in place that you can still see the ground glass, its pretty dark and I have to be under the cloth for about 30 seconds for my eyes to adjust enough to see. Then I will refocus. But its only a 2-3 millimeters at the most using a 90 mm lens and around 3-4 millimeters on others (4x5), if at all. When I first started using IR film I was WAY over compensating for focus shift and not stopping down enough.

[vinny]

I've never compensated for large format efke ir films. Compensation does vary between individual lenses but it's so small that I don't worry about it. My prints aren't soft.

[Jody_S]

My imagesetter film is sensitive well past 850NM, I've always shot at f16 or smaller and never had to make an adjustment for focus.

[uphereinmytree]

I agree with 'no large format focus adjustment needed for efke IR film' I always get sharp images. More sensitive IR films would need adjustment and I do the adjustment when shooting 120 IR in a 645 camera.

[drew.saunders]

When I shoot Efke IR820, I try to focus on the something that's close that I want to be in focus, but don't specifically change focus, and use f/16 or 22 for 4x5. For your 8x10, I'd suggest f/32, 45 or 64, plus a lot of patience!

[Leigh]

At the shooting apertures commonly used for LF work, the IR shift will usually be well within the depth of field.

- Leigh

[stray_227]

Thanks folks - lot of good advice which I really appreciate! I've just gotten to the point where I think I have the exposure down - which took a LONG time - this film is tuff and I'm a rookie - but I'm committed. Will have to deepen my tests on the focusing front now.

thanks again for all of the great comments!


On a different but related topic - if people have specific developer suggestions for this film I'd love to hear about that as well

shawn

[Joseph O'Neil]

Stop down as much as you can. Also, I find that focusing with IR is more critical if you are using longer focal length lenses (210mm or longer for 4x5, for example) and if you have any of it around, the old Kodak HIE was more sensitive than the newer IF films. I think, not sure, the old HIE went to at least 850nm

If you ever do a IR conversion on a digital SLR, feel free to e-mail me off forum, I did that with one of my D7000s, and it is great fun. For what it is worth, if you can shoot 4x5 IR, you will take nicely to a digital IR conversion.

good luck