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Contents

• Description
• Long-Exposure Effects
• Short-Exposure Effects
• Adjustments for Long and Short Exposures
• Black-and-White Films
• Color Films

DESCRIPTION

The reciprocity law states that the intensity of light falling on a photographic film multiplied by the exposure time equals the total amount of exposure.

Intensity x Time = Exposure

This means, for example, that an exposure of f/16 at 1/60 second is equivalent to an exposure of f/11 at 1/125 second. In either combination of settings, the same amount of light reaches the film.
The reciprocity law applies to most black-and-white and color films at exposure times from approximately 1§5 second to 1/1,000 second. (See the tables in this publication for individual product characteristics.)
However, all photographic emulsions are subject to an effect often called "reciprocity-law failure." At exposure times outside the above range, you will begin to see underexposure (loss of effective film speed) at the normally calculated exposure setting, a change in contrast, a color shift, or a combination of these effects. The word "failure," in this context, does not imply a shortcoming of the film, but merely that the reciprocity law does not hold for very long or very short exposures times.
We also sometimes refer to these changes in film response to particular illumination levels as "long-exposure effects" and "short-exposure effects."

LONG-EXPOSURE EFFECTS

Under low-light conditions, you may have to extend your exposure times to a point of significant speed loss. With black-and-white films, the effect of this speed loss is partially offset by wide exposure latitude. Most color films require more than the normally calculated exposure when the lighting is unusually low. Also, the sensitivity differences between the many layers of color films can cause a color-balance shift, which means that you will sometimes need to use color-compensating filters to achieve an acceptable color balance.
When you must increase the indicated exposure to compensate for long-exposure effects (see the data in the tables), use a larger lens opening if possible. Extending the exposure time will result in more speed loss, contrast change, and color shift.

SHORT-EXPOSURE EFFECTS

Extremely short exposures produce essentially the same effect as long exposures: speed loss. There is also an increased scattering of exposed silver halide grains, the formation of smaller latent-image centers, and a lower rate of development at the latent-image centers.
The short-exposure effect appears as lower contrast or reduced density in the negative. Exposures of 1/1,000 second or shorter can cause this problem.
KODAK T-MAX Professional Films, KODAK EKTAPAN Film, and most KODAK Color Films have been designed to minimize the short-exposure effect.

ADJUSTMENTS FOR LONG AND SHORT EXPOSURES

Black-and-White Films

Use the exposure and development adjustments in the table below for these black-and-white films:
KODAK EKTAPAN Film
KODAK PLUS-X Pan Film
KODAK PLUS-X Pan Professional Film
KODAK TRI-X Pan Film
KODAK TRI-X Pan Professional Film
KODAK VERICHROME Pan Film
Adjustments for KODAK T-MAX Professional Films, KODAK Technical Pan Film, or KODAK Commercial Film are listed in Tables 2, 3, and 4.

Table 1
Exposure and Development Adjustments
for Most Black-and-White Films

1. Not applicable to EKTAPAN Film
2. Not recommended for TRI-X Pan Professional Film
3. EKTAPAN Film does not require an adjusted development time at 1/1000 second.

It may be difficult to use the previous table to estimate the adjusted exposure times for indicated times between 1 and 100 seconds. The following graphs (Illustration 1) will help you find the adjusted exposure times for times between those given in the table.

Table 2
Exposure and Development Adjustments
for Long and Short Exposures:
KODAK Commercial Film

Table 3
Exposure and Development Adjustments
for Long and Short Exposures:
KODAK Technical Pan Film (developed in KODAK TECHNIDOL Liquid
Developer or KODAK HC-110 Developer [Dil D])

Table 4
Exposure and Development Adjustments
for Long and Short Exposures: KODAK T-MAX
Professional Films

Note: KODAK T-MAX Professional Films do not require a development-time adjustment.

Table 5
Exposure and Development Adjustments
for Long and Short Exposures: KODAK PROFESSIONAL T-MAX
Black-and-White Film T400 CN (Process C-41)

Color Films

Table 6: Exposure Adjustments and Filter
Compensation for Color Reversal Films

Table 7
Exposure Adjustments and Filter Compensation for
Color Negative Films

* NR=Not recommended for critical use

Table 8
Filters and Exposure Adjustments for KODAK Color
Films with Fluorescent Lamps

* Exception: KODAK EKTACHROME 100 Professional Film / EPN
**When the type of fluorescent lamps is unknown, try the filter(s) and exposure adjustments given; color rendition will probably be less than optimum.

Note: Except for the KODAK WRATTEN Filters No. 85 and 85B, all filters are KODAK Color Compensating Filters (CC). Increase exposure by the adjustment given. Cyan, magenta, and yellow filters were used unless equivalent values of red and blue filters could reduce the number of filters or minimize the exposure adjustment. Red filters were substituted for equivalent values of magenta and yellow. Blue filters were substituted for equivalent values of cyan and magenta.
To avoid the brightness and color variations that occur during a single alternating-current cycle, use shutter speeds of 1/60 second or longer with fluorescent lamps.

Table 9
Filters and Exposure Adjustments for KOOMGDAK Color
Films with High-Intensity Discharge Lamps

* Exception: KODAK EKTACHROME 100 Professional Film / EPN
** This is a high-pressure sodium-vapor lamp. The information in the table may not apply to other manufacturers' high-pressure sodium-vapor lamps because of differences in spectral characteristics. Kodak does not recommend sodium-vapor lamps for critical use.
*** To avoid affecting image definition and contrast, we recommend that you use no more than 3 color compensating filters.
This combination, which includes 4 filters, is an exception to that recommendation.

Note: All filters are KODAK Color Compensating Filters (CC). Increase exposure by the adjustment given. Cyan, magenta, and yellow filters were used unless equivalent values of red and blue filters could reduce the number of filters or minimize the exposure adjustment. Red filters were substituted for equivalent values of magenta and yellow. Blue filters were substituted for equivalent values of cyan and magenta.

To avoid the bright ness and color variations that occur during a single alternating-current cycle, use shutter speeds of 1/125 second or longer with high-intensity discharge lamps.

Note: The reciprocity data in this publication represent products tested under the conditions of exposure and processing specified. They are representative of production coatings and, therefore, do not apply directly to a particular box or roll of film. They do not represent standards or specifications that must be met by Eastman Kodak Company. The company reserves the right to change and improve product characteristics at any time.

For critical use, make tests with film of the same emulsion number that you will use for the final exposure. The emulsion number is stamped on each box of film.

Kodak, Advantix, Elite, Ektacolor, Ektapan, Ektar, Gold, HC-110, Lumiere, Kodachrome, Plus-X, Royal Gold, Technidol, T-Max, Tri-X, Verichrome, and Vericolor are trademarks.