Infrared focus point for Hasselblads

scinysnaps · Dec 13, 2009

How do you focus for infrared film on Hasselblads?
I have 2 old C* lenses. Can't seem to find and IR dot as on a Nikon lens.

Q.G. · Dec 13, 2009

The hard way, i'm afraid.

Where the IR index would be depends on the lens type and wave length.
What lenses do you have, and what wave length would be the one you're going to use?

scinysnaps · Dec 13, 2009

I have a 80mm C* and a Distagon 40mmC*
I am thinking of using the Rollei Infrared film

Ed Sukach · Dec 13, 2009

The more I think about it ...

Unless the film is LOCKED into a *very* short-wave UV area and a severe UV filter ("opaque" to normal vision) is used I don't think the "UV" compensation mark is useful, or even appropriate.

With a relatively mild filter, #25 Red or so, the light affecting the film is alredy modified, so the image on the ground glass, visible to "usual" vison, would be focused properly, anyway.

I have done a fair amout of IR, with Konica and a #25, and was troubled with many exposures out of focus. Analyzing: I had first focused with the #25, then shift using the IR dot. NOT good. Even focus wthout the #25, place it on the lens and shift. Still, the correction from the shift to the IR dot is too large.
I will use the available IR films, I think Kodak's is no longer available, I'll focus WITH the #25 in place and forget andy tweaking, as if it was plain old B&W film.

One thing I have not done yet is to compare IR and plain B&W film with the #25 filter. It would NOT surprise me to find that there wasn't much difference.

msage · Dec 13, 2009

scinysnaps said:
How do you focus for infrared film on Hasselblads?
I have 2 old C* lenses. Can't seem to find and IR dot as on a Nikon lens.

Hi
I have never adjusted for focus (4x5, 120 and 35mm).
Michael

martinhughesireland · Dec 13, 2009

I never adjust focus either
In theory you should change focus but in the real world it makes no real visible difference
The only exception might be for macro photography or if your shooting with a very narrow DOF, then you might notice it...

Just get out and shoot a role and focus as normal....

M

Q.G. · Dec 13, 2009

scinysnaps said:
I have a 80mm C* and a Distagon 40mmC*
I am thinking of using the Rollei Infrared film

The IR mark is 10.5 mm to the right of the focus index for the Planar, and 5.5 mm to the right of the index mark for the Distagon.
Both for 800 nm.

The spread is quite large going through the bandwidth from 660 nm to 900 nm: from about 5 mm to almost 15 mm to the right of the visual focus mark on the Planar, and 2.5 to 7.5 mm on the Distagon.
So stop down a bit more than you would otherwise, to get DoF to help a bit.

If you want trouble free focussing, get the Sonnar-Superachromat or UV-Sonnar. No correction needed, everything in focus from deep blue (UV in the latter case) to IR, all at once.
What you would need is a lot of cash to get you one of these lenses.

Q.G. · Dec 13, 2009

Ed Sukach said:
The more I think about it ...

Unless the film is LOCKED into a *very* short-wave UV area and a severe UV filter ("opaque" to normal vision) is used I don't think the "UV" compensation mark is useful, or even appropriate.

The more i think about it, noone mentioned UV and UV index marks.

Ed Sukach · Dec 13, 2009

Oh boy..... another "Senior Moment"!!!

You are correct ... I was thinking "Infra Red" - "IR" - and writing "UV" - just the opposite.

Howevertheless ... I think IR indices are no longer needed/ appropriate ... evidenced by their omission by Hasselblad/ Zeiss.

scinysnaps · Dec 13, 2009

Q.G. said:
The IR mark is 10.5 mm to the right of the focus index for the Planar, and 5.5 mm to the right of the index mark for the Distagon.
Both for 800 nm.

Would this be with the 25 red only or does it apply to the IR 87/87C as well?

keithwms · Dec 13, 2009

Newer APO/ULD/ED glass will likely not require correction with the current crop of near-IR films, especially if you are only filtering to the red or deep red. If you use a deeper cutoff filter (rm72 or deeper) then you may well need to correct a bit and/or stop down preventively.

With older lenses you may wish to focus a bit nearer than normal (to the near point of your composition) and then stop down as much as needed to bring your far point back into focus. In other words, enclose your near/far points by a safety margin. I explained why to focus nearer in some old post somewhere... it has to do with the refractive index as a function of wavelength for typical (non-apo/uld) glass.

If you want to use shallow DOF then IMHO there is no option but to shoot apo glass... even if you are using the near-IR films. (Mind you, with the IR I do, I am generally using a #87, which is quite a high cutoff and I gather that most people don't go that far with the current films)

With superpan and a deep red filter I can report that I saw no focus shift, shooting wide open at ~f/3.5 on a mamiya 6.

I can also report that I have needed no refocus with the RB 210 KL apo, with Rollei IR and superpan.

My main advice with IR film is, if you have doubts: shoot, bracket exposure, bracket aperture, refocus, and shoot some more, and keep doing that until you gain confidence.

2F/2F · Dec 13, 2009

I assume that opaque or near-opaque filters will be used, because otherwise, no IR film made now gives anything like the "classic" IR look. Using any current b/w IR film with a #25 or #29 filter won't look all that different than using the same filters on a regular panchromatic film, and certainly will not give the "classic" IR look.

Info on the necessity of focus shift using Rollei IR with an R72: http://www.digitaltruth.com/products/product_tests/infrared_film_007.php

In short, if you want the sharpest image, you should shift focus.

The same should hold true Efke IR with an R72, as it has about the same max sensitivity of 820 nM.

Here is the index page for all the IR film info on this Website (and info on Rollei ATP): http://www.digitaltruth.com/articles.php.

IMO, these short reads on the current b/w IR films are the most useful to be found on the WWW. They are simple, straight forward, and practical. I would read them all to get some helpful starting information.

So, in summary, IMO:

1. There is little-to-no point in using any of the current IR films with anything but an opaque or near-opaque filter, if a "classic" IR look is desired.

2. Focus should be shifted when using IR films with these filters, if you want the plane of focus to be right where you focused in the viewfinder (though this should not be necessary if using them with shallower red filters such as #25 and #29).

P.S. Ilford SFX is not an IR film, so is not included in these comments. It will work with an R72, however, and this will give the most extreme effect with this film.

scinysnaps · Dec 13, 2009

Yes, I am planning to use an 87 IR filter with the Rollei IR film
Great stuff guys
Thanks a lot.. I will read those articles
Cheers

Q.G. · Dec 14, 2009

Ed Sukach said:
Howevertheless ... I think IR indices are no longer needed/ appropriate ... evidenced by their omission by Hasselblad/ Zeiss.

Well, no.

The earlier lenses do indeed not have the index mark, because such a thing depends so much on dominant wavelength.
They were, and are, still needed, but not appropriate to put just one single mark on the lens.

But, despite that all, later lenses do have such a mark.
Market pressure, people asking about it, perhaps?

Hard to explain adding an IR index mark as evidence - by omission - that such a thing is no longer needed, isn't it?

And 2F/2F is absolutely right: you must correct for the wavelength.

Q.G. · Dec 14, 2009

scinysnaps said:
Would this be with the 25 red only or does it apply to the IR 87/87C as well?

That would be the correction needed to bring light having a wavelength of 800 nm to a focus in the plain were the film is.
No matter what filter.

As mentioned before, the spread in focal length for different parts of the (near) IR spectrum is quite large, and you have to decide (and control) which part of the spectrum to use, and which bit to bring to focus on the film.

I did mention that the way to do it was "the hard way", didn't i?

The easy way is to use a Sonnar-Superachromat. It brings all light to a common focus, from deep blue to 1000 nm IR.
Two drawbacks. A 250 mm focal length. And rather expensive.

polyglot · Dec 14, 2009

Stopping down might cure any focus errors but be aware that you will do a real disservice to your image sharpness - the long wavelengths of IR mean that you will get diffraction effects at larger apertures. Blue is about 480nm, the near-IR range these films are sensitive to is usually 720-820nm, which is about 50-70% longer. So you will get softening due to diffraction a whole 1-1.5 stops earlier.

Of course, some IR films can be pretty crunchy so the extra softness may well be hidden by the coarseness of the grain and you can go ahead and stop down.

And you people ragging on SFX for not being an IR film? Yes, you, 2F. BS. It records a distinct (if tiny) frequency band that the human eye is insensitive to, as evidenced by its showing the Woods Effect on green foliage and an R72 filter. Sure there are other films with better sensitivity and to longer wavelengths, but SFX definitely extends outside the human range of sensitivity.

2F/2F · Dec 14, 2009

SFX is a lovely film. I did not "rag" on it. I said that "Ilford SFX is not an IR film." Additionally, Ilford does not claim that it is, and would make the same statement I made if asked. It is a near-IR/extended-red-sensitivity film, through and through.

I also said: "It will work with an R72, however, and this will give the most extreme effect with this film."

Ilford SFX is sensitive to almost exactly the same frequency range as the human eye/brain. It doesn't see anything we can't see...it just sees it in a different ratio to the more easily visible wavelengths than we do. Whatever "Woods" rolleyes: - His name was Robert Wood, with no S) effect you see with SFX is visible to the eye...if you block all the other wavelengths from hitting your eyeballs in order to keep them from overwhelming the deep red ones. When I look through a camera with an R72 filter mounted on a bright and contrasty day with nice puffy clouds, I see a dark sky, white clouds, and light plants (with only an f/2.8 lens, no less)...and so does Ilford SFX.

What is it with the uppity Australian residents who can't seem to read lately? Is it coincidence that the last person who started BS with me over a very moderate statement, and quoted implications to me that I did not make is also located there?

Infrared focus point for Hasselblads

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