INFRARED PHOTOGRAPHY

The following information is provided as a service by Doug Earle and is intended for personal use only.  Publication or redistribution is prohibited without express written consent of Doug Earle.

These are organized notes of mine taken during two workshops in Infrared Photography taught at the Southwest School of Art and Craft in San Antonio. The instructor was Tim Summa, then Chair of the Photo Dept. I’ve prepared these as a personal review and to better organize the material, but offer them as a tool to assist others who work in this challenging and often frustrating medium.

The following topics are covered:

1. Light: Visible and Invisible Spectrum
2. Filters:
3. Infrared Films: Kodak High Speed Infrared and Konica
4. Photographic Techniques
5. Darkroom and Printing
6. Other Resources and links

1. LIGHT: VISIBLE AND INVISIBLE SPECTRUM

Light is a form of radiation wave energy that exists in a spectrum of which the human eye can see only a portion, that being the Blue to Red spectrum. Below the blue is "ultra violet" light, above the red is "infrared light".

The table below shows the wavelengths (expressed in millimicrons, or one millionth of a millimeter) of light in the spectrum, with the visible light portion between 400 (Blue) and 700 (Red)

Kodak High Speed IR is sensitive in the Violet to Green range (400—530) and in the red and Infrared range (680 to 900 +/-).

Konica IR is sensitive throughout the visible range of Violet to Red (400 to 700) and in the lower end of the Infrared range of 750 to 780.

Natural Light or Daylight consists of SUNLIGHT and SKYLIGHT

SUNLIGHT contains the whole spectrum of light (RGB & IR). It sparkles and is directional.

DAYLIGHT contains only the Blue portion and is scattered light

IR films only see SUNLIGHT. Since sunlight is directional if you face away from the light source (the sun), the IR film "sees" no light and produces a black sky. Facing in to the light source, it registers much light and produces a light sky.

2. FILTERS

There are five common filter types that are used in Black and White photography:

A. Tricolor

B. Minus

3. Polarizing
1. Neutral Density
2. Infrared specialty filters

The first four only effect the visible light spectrum and allow essentially all the IR light to pass.

Filter names/numbers are based on the KODAK WRATTEN SYSTEM which sets the technical standards and specifications for light transmittal.

Filters come in a variety of manufacturers and types. Many of us use a skylight filter as a matter of course, to eliminate UV light. This is a #1a filter on the Wratten scale.

Some filters are available from limited manufacturers and/are expensive, especially if purchased in optical glass mounted screw in or square filters. An inexpensive alternative are Gelatin Filters made by Lee Optical. These come in 3" or 4" squares and can be mounted in a holder made by Lee, in a universal Cokin holder, or simply held in front of a lens on a tripod mounted camera. An optical glass filter from Kodak costing $50.00 or more can be purchased in a Lee Gel for around $15. The disadvantage is that they do scratch easily as I found out by placing one too close to the front of a zoom with a telescoping front element.

1. TRICOLOR—Pass 1, absorb 2

Tricolor filters allow 1 color light to pass and absorb the other two on the RGB scale.

The # 25 Red filter is often used in IR photography as it eliminates the Blue light to which the IR film is sensitive and allows the Red and IR to pass.

2. MINUS FILTERS—Pass 2, absorb 1

Light loss from either of these filters is approximately 1 to 1 ½ stops, effecting only the visible spectrum.

Either of these filters are very good for nature photography. It was reported that Ansel Adams used a #12 filter on most of his landscape work.

3. Polarizing Filters

These filters eliminate the scattered blue skylight so that pure Sunlight is what is registered.

4. Neutral Density

These smoky gray filters add absorb evenly over the entire visible spectrum. They reduce by some percentage or factor the amount of visible RGB light that passes. They do not effect IR light, allowing essentially all the IR light to pass.

They are helpful for three purposes:

1. Reducing the amount of light that passes so that a slower shutter speed or wider aperture for less depth of field (or both) can be used;
2. As an easy way of bracketing visible light so that changing camera settings isn’t necessary;
3. In the case of Konica IR, as a tool to balance the ratio of Visible Light to IR Light.

Wratten System uses a 3/10’s designation system to indicate Neutral Density effect. This is described by the chart below:

When used with other filters you add the cumulative stops lost.

For Example:

5. INFRARED FILTERS

These filters exclude visible light entirely and allow varying degrees of IR light to pass.

The #87 Filter is for Kodak High Speed IR, which has a film sensitivity in the IR range of from 750 to 900. This filter passes almost 90% of the IR light at the high end of the range, and lesser amounts at the lower end.

The #89 B is the only IR Filter that works with Konica IR. This film is sensitive in a very narrow IR band, from 750 to 790 +/-. Whereas the # 87 filter allows very little IR to pass in this wavelength, the #89B allows substantially larger amounts.

The 87C filter is recommended for Digital IR photography.

The chart below will give you an idea of the transmittal rates: Percentages shown are percent of light transmitted through the filter. Figures are rounded.

3. Infrared Films:

1. Kodak High Speed Infrared

Kodak High Speed Infrared is a true infrared film with a broad range of Infrared sensitivity (see chart above). The emulsion is sensitive in the Blue and Red spectrums also. This film may be rated at E.I 200 or 125, but bracketing over and under by at least one stop is recommended, as the amount of infrared light is an unknown variable in any photograph. This film is suitable for outdoor and studio work, with either hot lights or flash.

2. Konica Infrared

Konica Infrared is in actuality two films in one. It is a fine grained, slow speed visible light film emulsion combined with an extremely slow, narrow range Infrared sensitive emulsion. The Visible Light emulsion has an EI (ASA, ISO) of 30, while the Infrared emulsion rates somewhere around E.I. 3 or 6! Threfore, there is a 2 ½ stop difference between the E.I.’s of the emulsions:

Because of this it is possible to combine Visible and Infrared light images in the same photo in varying combinations.

By use of ND filters, you can have:

1. Predominant Visible Light, with little IR (use no filter)
2. Balanced Visible and Infrared Light (use approximately 2 ½ stops ND)
3. Predominant Infrared and little Visible (use more than 2 ½ stops ND)
4. Exclude Visible light (by using a #89B filter)

See the photo techniques for further explanation.

4. Photographic Techniques:

With Infrared Photography a certain amount of guesswork comes into play, which means that experimentation is necessary to determine proper exposures. This is because camera and light meters read only the Visible Light spectrum so the amount of IR light is an unknown, and; the amount of IR light varies by season and altitude. As a general rule, Infrared Light is highest in Summer and is approximately 1 Stop Less in Winter, and halfway between in fall and spring. However over 5000 feet altitude you gain 1 Stop of IR exposure due to the effects of a thinner atmosphere.

A good starting point for determining exposure is to use the "Sunny 16" rule: In full sun proper exposure is f 16 @ 1/film E.I. Thus, for a familiar film (say T-max 100) shot at the beach on a sunny day, you set your camera to f16 and expose at 1/100^th second and you’ll be close. However, as mentioned before, IR emulsions don’t have a definite E.I. rating. Experimentation has shown that for Kodak HS IR a rating of 200 or 125 is a good starting point and for Konica a rating of 6 for the IR portion is a starting point. Bracketing should be done to maximize chances for this to work. Adjustments should also be made for time of year, less than full sunshine, or altitude.

EXAMPLE: Assume Kodak HS IR rated at E.I. 125, being used on the beach on a bright sunny day.

"Sunny 16" exposure is f 16 @ 1/125

Remember that filters only effect the Visible Light portion of the spectrum and have no effect on the amount of IR light passing through. Thus, you do not make an adjustment for the filter factor as you do for visible light photography. Even with a Red Filter (which causes a loss of 2 to 2 ½ stops) your exposure in the above example would be f 16 @ 1/125 in the sun. All the red filter does is remove the Blue and Visible red light from the exposure.

2. Kodak High Speed Infrared.

The above suggestions work well with Kodak HS IR when used outdoors.

This film also is suitable for studio work with either hot lights or flash.

When using flash the MAXIMUM IR output comes at ONE-HALF Power and not full power as one might expect. The chart below gives the variance of IR output (approximate)

3. Konica IR

Given its extremely slow IR speed, Konica IR is appropriate only for daylight use and is not suitable for flash or studio work.

Remember that you are, in essence, working with two films: a Visible Light ISO 30 rated film and an IR Light ISO ~6 rated film. This means that you can have the following possible exposure values for the film.

1. Predominant VL, little IR

For this, simply meter using the camera or hand held meter rating the film at ISO 30 at the desired shutter speed, and perhaps bracket around that point. Essentially you’ll have a slow, fine grained VL negative with a slight IR effect (perhaps).

2. Balance VL and IR

This approach involves the following steps. The example given presumes summer full sun for simplicity’s sake.

1. Using the Sunny 16 rule, set the exposure for the IR portion of the emulsion: f 16 @ 1/6 th sec
2. Now adjust the VL to balance by adding Neutral Density filters. This would mean adding 2 ½ stops Neutral Density filtration. [Remember, using the sunny 16 rule the VL proper exposure would be f 16 @ 1/30^th sec. . The difference between 1/30^th sec and 1/6^th sec is 2 ½ stops:

{each # in sequence represents one stop. * is halfway between or 1/6] 1/30, 1/15, 1/8, *,1/4

3. If the shutter speed of 1/6^th second is too slow, then adjust the aperture to the equivalent exposure for the shutter speed desired. Decreasing shutter speed requires opening up aperture, adjust with ND filters and bracket like crazy.

3. Predominant IR with Little VL

This follows the same principle as the previous example, except that you increase the amount of ND filtration to an exposure below that of balanced VL/IR. (that is, if 2 ½ stops ND balance VL and IR, then 4 stops ND reduces VL below that of IR.

4. Only IR.

Rate at ISO 6, using the sunny 16 rule. Add a #89B filter to exclude all VL. Adjust shutter speed and/or aperture as needed and bracket.

NOTE: At small apertures (f 1/16) there is sufficient depth of field so that IR focus adjustment may not be required. At larger apertures (f 8 and above), the use of the lens’ IR focus adjustment will probably be needed to assure proper focus. Length of lens should always be taken into consideration as well.

5. Darkroom

Develop in D76 @ 68 to 70 degrees for 11 to 13 minutes, with 5 second agitation every minute.

Stop bath for a full 5 minutes. (Failure to use a long stop can result in pitting in the emulsion"

Fix in two baths of 5 minutes each.

Wash per instructions.

2. Konica

Develop in D76 or Rodinal (1:35) @ 68-70 deg. For 6 minutes +/- with above agitation

Stop, fix, wash as per above.

VI.    Other resources and links 

        The Texas Photographic Society has a very good tech paper on Infrared Photography.

Southwest School of Art and Craft

Infrared Photography Forum for posting photos and answering questions

If you know of other helpful resources please send them to me along with your name and a brief description of content and why you found them helpful and I'll add them to this listing.  Send Email by clicking here.