Help with infrared focussing please :)

[Kye395]

Looking to get into IR photography so naturally ive been researching it. I plan to shoot on Rollei Superpan using a Mamiya RB67 with a 65mm Sekor f4.5 lens and a R72 filter, om going to shoot brackets between ISO 6 @ f11 and ISO 12 @ f11 since its my first test with IR.

My issue is with focussing for IR, ive read about and understand that IR focusses on a different plane slightly before visable light but im not sure the correct way to adjust for this on the bellows system on the 67 since my lens has no IR markings.

Do i just move the bellows forwards from infinity focussing a few mm or is there another way to do it?

thanks

 

[Paul Howell]

As I understand it there are no true IR films on the market, The current batch are extended red sensitive, but not IR, so just focus as you normally do?

 

[MattKing]

Welcome to Photrio.
The need to adjust focus for IR photography arises because of the variance between the wavelengths of visible light and light in the IR range.
Historically, with films like Kodak HIE, the film was sensitive a long way into the IR range - almost 900nm - so a fairly significant adjustment in focus was necessary.
The current films with some IR sensitivity don't go nearly so far into the IR range, and as a result if one were to adjust focus, the adjustment would be much smaller.
@Paul Howell has it correct - its barely worth bothering with.
If I were working at close distances, I'd probably make sure by using f/11 or smaller apertures.
For more distant objects, you can probably use any aperture available, and will still be saved by depth of field.
If you were using a true IR film like HIE, the manual for the later RZ Pro II camera includes a chart listing the suggested very slight adjustment - good luck making a 0.24 mm change!:

 

[Kye395]

Welcome to Photrio.
The need to adjust focus for IR photography arises because of the variance between the wavelengths of visible light and light in the IR range.
Historically, with films like Kodak HIE, the film was sensitive a long way into the IR range - almost 900nm - so a fairly significant adjustment in focus was necessary.
The current films with some IR sensitivity don't go nearly so far into the IR range, and as a result if one were to adjust focus, the adjustment would be much smaller.
@Paul Howell has it correct - its barely worth bothering with.
If I were working at close distances, I'd probably make sure by using f/11 or smaller apertures.
For more distant objects, you can probably use any aperture available, and will still be saved by depth of field.
If you were using a true IR film like HIE, the manual for the later RZ Pro II camera includes a chart listing the suggested very slight adjustment - good luck making a 0.24 mm change!:
View attachment 400901

Thank you so much for the info, really appreciate it, especially the correction table fr the manual

 

[Sirius Glass]

Welcome to Photrio!

Other than with Kodak HIE in the past, I have not needed adjust for the the infrared focus.

 

[MattKing]

Thank you so much for the info, really appreciate it, especially the correction table fr the manual

You are welcome - but don't forget that following that table will cause you to over-correct if you are using one of the modern near-IR sensitive films.

 

[mshchem]

Matt has a good point about over correcting. The tables are for IR wavelengths. With Currently available films I suspect you wouldn't get any improvement in sharpness, maybe make it worse.

I remember playing with Kodak HIE decades ago. I didn't really know how to get the most out of it. Box had great warnings about opening only in a darkroom.

 

[Kye395]

Matt has a good point about over correcting. The tables are for IR wavelengths. With Currently available films I suspect you wouldn't get any improvement in sharpness, maybe make it worse.

I remember playing with Kodak HIE decades ago. I didn't really know how to get the most out of it. Box had great warnings about opening only in a darkroom.

You are welcome - but don't forget that following that table will cause you to over-correct if you are using one of the modern near-IR sensitive films.

Okay, I’ll be using rollei superpan which a quick google says goes up to 800nm. What should I do with this particular film?

 

[mshchem]

Hoya recommends digital capture in raw, estimated 10 stop exposure correction. If I was shooting film, panchromatic film I would focus normally and test.

This fellow is an expert. Member here.

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Multi-format film photographer working mainly in alternative processes, such as Carbon Transfer, Kallitype, Tri-Colour Gum, Cyanotype. Andy will take you with him when on short, photographic trips, and into the darkroom. Sometimes he tests out different film developers and films, with spicy...

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[mshchem]

HOYA | Reviews - Infrared photography with the HOYA R72 filter

hoyafilter.com

 

[reddesert]

A few remarks:

- In general since current films don't go as far into the IR as HIE, you can typically just stop down a little more and cover it with depth of focus. Perhaps an exception is if you were to use a very long, but non-APO, tele lens.

- In the days of HIE, old books would suggest a rough correction of adding 1/400 the focal length of extension. So for a 100mm lens, you would move focus forward by 0.25mm, and so on. This was useful for large format cameras/lenses that don't have IR marks. If you compare this rule of thumb to the values in the Mamiya chart above, it's not too far off for normal lenses, underestimates a little for (retrofocus) wide-angles, and overestimates for the APO teles (not surprising, given the apochromatization). Of course, you still have to scale the rule of thumb down, since we don't have HIE.

- The RB67 has a millimeter focusing scale on the focus distance chart on the side, and has about 23mm of travel per full turn of the focus knob (total 2 full turns of travel, I think). So if you turn the knob by 5 degrees you get about 0.3mm of extension. That amount of turn is about what you might be able to estimate by eye with a mark on the knob, or just read the millimeter scale for the offset if you want.

 

[Andrew O'Neill]

With the IR films available today, they only just barely reach into the infrared, unlike good old HIE. With HIE, the only time I did focus compensation was when I was using the opaque 87C filter. Back to the current IR films. Don't bother with focus compensation. Not necessary.

 

[F4U]

I should avoid Infrared film threads. I can't believe some small-time firm hasn't put together a small film coating line and mixed up a batch of HIE emulsion and coated it, slit it and marketed it. If Kodak could do it 80 years ago and made money on 20 foot wide film coating lines, you would think some small time firm could do it on a 18 inch wide coating machine. Vern Estes built model rocket empire on a home made engine making machine he called Mabel.

 

[reddesert]

Generally, making films (or semiconductor detectors) more sensitive in the infrared is difficult. Speaking very generally, photons in the near-IR have lower energy than photons in the optical, so they are less likely to activate a photosite and be absorbed. Thus, infrared B&W emulsions probably have fairly sophisticated sensitizing dyes that allow the absorption of near-IR light and convert it to the activation of silver.

The opposite is true of the blue and near-UV - blue photons have more energy and more easily provoke a reaction, that's why early emulsions were blue sensitive and it took longer to develop ortho and then panchro film.

There were once specialized blue and red and near-IR emulsion on plates for things like scientific astrophotography - IIIaJ, IIIaO, IV-N, etc. All gone now. The amount of R&D in emulsions like these and HIE was no small matter.

 

[250swb]

Looking to get into IR photography so naturally ive been researching it. I plan to shoot on Rollei Superpan using a Mamiya RB67 with a 65mm Sekor f4.5 lens and a R72 filter, om going to shoot brackets between ISO 6 @ f11 and ISO 12 @ f11 since its my first test with IR.

My issue is with focussing for IR, ive read about and understand that IR focusses on a different plane slightly before visable light but im not sure the correct way to adjust for this on the bellows system on the 67 since my lens has no IR markings.

Do i just move the bellows forwards from infinity focussing a few mm or is there another way to do it?

thanks

Using f/11 you don't need to compensate especially with a wide lens, the DOF will do it for you unless close focusing in which case focus bracket and make a mental/written note of how much ready for next time.

 

[xkaes]

While stopping down is one option -- and the general advice -- it's not always practical. Try it yourself.

With IR film, you are going to have to use a very slow speed or a very fast aperture -- or both. So when I'm shooting at 1/60 and f2.0, focusing is an issue.

I'd first run simple tests to get your film speed where you want it, and then run some simple tests to determine how much you need to adjust at the aperture(s) you are likely to use. If you plan on using f11 all the time, don't waste your time, but, if you plan on using wide f-stops, you might need to adjust things -- and put a small mark on the camera or lens for the correction.

One more point, the shorter the focal length of the lens, the more adjustment will be needed.

 

[Petrochemist]

A few remarks:

- In general since current films don't go as far into the IR as HIE, you can typically just stop down a little more and cover it with depth of focus. Perhaps an exception is if you were to use a very long, but non-APO, tele lens.

Actually APO lenses are often worse than achromats for IR.
An achromat requires 2 wavelengths to focus at the same point which is accomplished with a quadratic wavelength/focus distance curve. Generally lens designs will make the quadratic as flat as practical to minimize chromatic aberration.
APOchromats require 3 visual wavelengths to focus at the same distance so a cubic wavelength/focus distance curve is required.
Lens designers will concentrate on keeping the central visual portion flat & this can mean the extremes (IR & UV) are very steeply sloped.
Ultra apochromats exist that extend the flat region well into the UV & IR regions, but these are mega expensive & only slightly more common than hen's teeth.

These day's I cheat when shooting IR & use a full spectrum converted digital camera that allows me to see how the lens is focused at whatever wavelengths I'm recording.
Using film & bellows will make things considerably harder.

If following the recommendations further up thread leaves your images a bit soft, or requires apertures too small for your requirements add a few test shots to your next roll. Photograph a tape measure heading straight out from the lens (or scene with landmarks at a range of known distances, if longer distances are required) Focus visually on something near the distance you wish to use, shoot with the filter/film you plan on using & see what distance comes out sharp in the photo.

This will allow you to calculate how much focus shift is seen with your lens/distance/wavelengths, so this can be used one future occasions.

 

[Rick A]

I've shot a few rolls of Rollei IR 400 and Ilford SFX 200 using a Hoya IR72 filter using my Mamiya RB 67 and found there is no need to correct for IR focus.

 

[250swb]

While stopping down is one option -- and the general advice -- it's not always practical. Try it yourself.

With IR film, you are going to have to use a very slow speed or a very fast aperture -- or both. So when I'm shooting at 1/60 and f2.0, focusing is an issue.

I'd first run simple tests to get your film speed where you want it, and then run some simple tests to determine how much you need to adjust at the aperture(s) you are likely to use. If you plan on using f11 all the time, don't waste your time, but, if you plan on using wide f-stops, you might need to adjust things -- and put a small mark on the camera or lens for the correction.

One more point, the shorter the focal length of the lens, the more adjustment will be needed.

An average IR filter is six stops, so even with a 400 ISO film it makes it 12 ISO, so don't you think a tripod is a good idea this side of failure?

 

[xkaes]

Sure, a tripod is always an option, but if you don't want to use a tripod, you have to open up. I shoot lots of slow film, not just IR, without a tripod -- at a wide aperture. Try it, you'll like it.

 

[itsdoable]

Actually APO lenses are often worse than achromats for IR.
An achromat requires 2 wavelengths to focus at the same point which is accomplished with a quadratic wavelength/focus distance curve. Generally lens designs will make the quadratic as flat as practical to minimize chromatic aberration.
APOchromats require 3 visual wavelengths to focus at the same distance so a cubic wavelength/focus distance curve is required.
Lens designers will concentrate on keeping the central visual portion flat & this can mean the extremes (IR & UV) are very steeply sloped.
Ultra apochromats exist that extend the flat region well into the UV & IR regions, but these are mega expensive & only slightly more common than hen's teeth.

<snip>

I'll disagree and point out Zeiss apochromats place the 3rd wavelength in the IR. Although there is no guarantee that an apochromat has less chromatic aberrations, in practice stretching out the curve help reduce both lateral an longitudinal chromatic aberations in the visible region, hence the better performance. Zeiss superapocromat place the 4th wavelength in the UV, so you can focus in visible light, and have sharp UV or IR images.

Other brands with "APO" marketing can mean anything though...

 

[reddesert]

I mentioned apochromat telephotos partly because if you look at the Mamiya RZ67 lens table that Matt posted in post #3, the APO tele lenses all have an IR correction of zero, while the non-APO telephotos have a rather large IR correction (again, that was for HIE, and partly academic for the currently available extended-red-sensitive films).

It is possible to achromatize a doublet lens analytically using two elements of suitable glasses (different dispersions, like crown and flint) and computing at two wavelengths, solving for the two lens powers (focal lengths). It is also possible to apochromatize at 3 wavelengths with a triplet by solving an equation with 3 variables. Rudolf Kingslake works out an apochromatic triplet in "Lens Design Fundamentals," and the first of his examples has a color correction (focal length vs wavelength) that looks like a cubic equation and does vary strongly outside the design wavelength range. His further working out of it refers to a British patent from 1892 by Taylor for a long-focus apochromatic triplet telescope objective, so the idea has been around for a while. But this design isn't a practical photographic lens due to other aberrations, he points out.

Modern system lenses aren't designed that way, by solving a cubic. They have more than 3 elements, and they have to optimize for a variety of aberrations, off-axis image quality, lateral color, and so on, in addition to the longitudinal chromatic aberration. The lens designer will likely spend many iterations with a computer program and playing with constraints to settle on a design. They could let the color go wild outside the design wavelength range ... but for a modern "apo" lens, I suspect that isn't common. It's not really possible to say without looking at color correction curves for a variety of lenses, if those are published. If I had a large collection of apo (and non-apo) telephotos, I could record some IR focusing mark positions, but I neglected to acquire such a collection.

Thankfully, I think the OP wanted to use a wide angle lens, so they can double-ignore this digression.

 

[Petrochemist]

I'll disagree and point out Zeiss apochromats place the 3rd wavelength in the IR. Although there is no guarantee that an apochromat has less chromatic aberrations, in practice stretching out the curve help reduce both lateral an longitudinal chromatic aberations in the visible region, hence the better performance. Zeiss superapocromat place the 4th wavelength in the UV, so you can focus in visible light, and have sharp UV or IR images.

Other brands with "APO" marketing can mean anything though...

Superapochromats usually have one point in the IR & one in UV, but they are not common lenses.
Most Apochromats match focus for wavelengths in red, green & blue, while most achromats match red & blue.

Having the flat region of the cubic curve cover as much of the intended usage as possible is certainly desirable, but with brands where the cost of the lens is more of a design cosideration this can be fairly tight.