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Seizing the Night

A Guide to Existing-Light (Available-Light) Photography
by Al Olson

© 2006  a.c.olson -- Lighthouse at Peggy's Cove 2002
© 2002 a.c.olson -- Lighthouse at Peggy's Cove. Fuji NPH 400 film using a Nikon F100 camera with a Tamron 28-300mm zoom lens.

Making photographs under conditions where there is no strong, even source of illumination, such as the sun or studio lighting, can be a challenge, even for the professional photographer. Usually the illumination emanates from multiple sources such as spotlights, bare bulbs, headlights, stage lighting, illuminated signs, moonlight, fireworks, interior lamps, and even the faint glow of twilight. Determining the best exposure for such uneven lighting can be difficult to say the least. These situations are often referred to as nighttime, available-, ambient- or low-light photography.

Kodak prefers to call such lighting “existing-light” and they justify the use of this terminology in their Workshop Series as follows: Existing-light photography is sometimes called “available-light photography.” In this book, we’ll use “existing light,” because the word “available” opens a large loophole. Any extraneous lighting a photographer chooses to use or take along could be considered available, even if it becomes the primary light source. The term existing-light photography is less ambiguous. Note too, that some photographers, in deference to the dim light typical of many existing-light situations, have also dubbed it “unavailable-light photography.” It does seem that way sometimes.

The photographer normally engages in existing-light photography to create a mood or to portray the realism of a given event or situation where applying additional artificial light would make the image appear to be staged and synthetic. For all practical purposes, we are interested in situations where the sun is below the horizon and/or no special lighting setups have been prepared for photographic imaging. In other words the photographer will work with whatever light is available in the scene.

Problems and Methods

The challenge to the photographer is to select the best film and determine the best exposure that will produce a result that is close to his visualization of the image. The difficulty lies in the fact that the Subject Brightness Range (SBR) for different objects in, say, a street scene with different illumination sources may exceed the latitude of the film. The question is what parts of the scene should be metered to obtain the detail and retain the mood.

© 2006  a.c.olson -- Pagosa Bar 2006
© 2006 a.c.olson -- Pagosa Bar. Note the extreme SBR in the above example that was exposed on negative film. Although the image was made in late twilight, the long exposure resulted in a very bright sky. The neon signage and other lighting appears normal, but the shadow detail on the front of the buildings is very faint and an observer can barely make out the people sitting in the bar. Fuji Superia 400 film and Nikon F100 camera with a Tamron 28-300mm zoom lens.

Modern exposure meters will meter down to the dimmest of illumination so that we may obtain readings on even the darkest of the shadow areas, down to even -1 or -2 EV, assuming that some ambient light exists. However, cameras with autoexposure usually impose a limit of thirty seconds on the length of exposure even when a longer one may be more appropriate. Especially when one wishes to select a smaller aperture. This necessitates selection of the manual exposure mode.

Because most situations require analysis of the exposure in different parts of the scene, you will find the spot meter to be most helpful. In fact, a hand-held meter, separate from the camera, is the most convenient. There are circumstances where the light source is even and unidirectional where an incident meter may be used. But even a sunrise (which is even and unidirectional) is difficult to measure with an incident meter because of the backlighting and silhouetting that require compromises for the best exposure.

Film choice is also a major issue to best meet the challenge. Normally we will want a fast film with reasonably fine grain that has sufficient latitude to accommodate the extreme SBRs that are usually encountered. This will be examined in further detail below. The remaining elements for meeting the challenge of existing-light photography, aside from the camera and a good, fast lens, are a sturdy tripod and a cable or remote shutter release. Long exposures are the norm in existing-light situations.

If you are trying to photograph more dynamic situations such as sports, stage shows, or street scenes with people and/or vehicular movement, then a fast lens, f/2 or better, and a fast film, ISO 800 or higher, would be a good starting point.

There are situations where we would want to use films with slower ISOs. For example, when we are photographing moving objects or light patterns and we wish to capture the movement with longer exposures. These subjects may include fireworks, lights on carnival rides, illuminated fountains, vehicular traffic, and other nighttime subjects.

Digital Photography

© 2006  a.c.olson -- Ouray at Night Digital 2006
© 2006  a.c.olson -- Ouray at Night 2006
Top image: © 2006 B. Conkey. Image was made with a Panasonic digital camera.
Bottom image: © 2006 a.c.olson. Image is a 4-minute exposure made with a Linhof Technika IV, 4x5 camera with a Schneider 150mm lens on Kodak Portra 160 VC film.
For the purpose of comparison, the two exposures were made at the same time in nautical twilight. In the upper image (digital) the twilight sky is still bright enough to record on the chip, as are the spectral images of the lights. However the detail illuminated by these lights is not recorded to the extent that it is produced in the lower photograph (film).

Since the first writing of this monograph the capabilities of the digital camera have improved immensely in terms available pixels, sensitivity of the sensor chip, color correction under adverse lighting conditions, and reduction of sensor noise.

Advantages of digital SLR include: film is not wasted because of bad exposures (you can make many trial and error images); you have instant review of the image and therefore you can reshoot it if necessary; you are able to select your choice of ISO; and you can make an immediate evaluation of your selected exposure. The characteristic curve of the digital chip is similar to that of transparency film (see discussion below) with a straight-line portion slightly less than 5 EV.

On the downside for night photography, selecting the higher ISOs causes an increase in pixel noise. Spectral highlights when overexposed, as they usually are at night, will “bloom” on most chips far worse than film.

The images above were made in nautical twilight (about 40 minutes after official sunset, which is my favorite time for night photographs because the twilight sky balances well with the terrestial ambient illumination). The bottom photo is a four minute exposure, made on ISO 160 film with an aperture midway between f/8 and f/11 with a large format, 4x5 camera. Note that you can see much more detail on the ground and around the lights. In addition to the fact that the film is less susceptable to the blooming of the lights, the larger format also increases their separation and produces more natural looking detail.

© 2006  a.c.olson -- Denver Mall 1990
© 1990 a.c.olson -- Denver Mall. This image was made with Kodak Ektachrome film using a Nikon F2 camera with a Vivitar Series I, 35-85mm Varifocus lens.
The scene above was made on transparency film but, because the characteristic curve for the digital chip is similar to transparency film, this scene would be well-exposed in a digital camera.

It should be noted that digital cameras operate best when there is significant ambient light in the scene. This means that it is unlikely to attain a quality outdoor photograph when it is darker than civil twilight, unless it is a street scene that is well-illuninated otherwise.

It is reported that one of the problems with long exposures on digital cameras is that they overheat and that this is one of the causes of digital noise. The better cameras of recent design are reported to support exposures up to 15 seconds and longer with supplemental power packs. One other drawback of the digital camera is its dependence on battery power. The battery drain problem actually applies to all cameras that are automatic and battery operated. Long exposures cause a drain the batteries. Manually operated cameras do not suffer this problem.

Exposure Values (EV)

For purposes of distinguishing between an adjustment to the lens aperture, which we will refer to as an “f-stop,” and a general exposure adjustment that could be either an adjustment to the aperture or shutter speed, we will refer to it in this text as an “exposure value” or EV.

Exposure Values, originally called Light Values, were first introduced by Prontor Shutter at the 1954 Photokina. A specific EV encompasses all equivalent combinations of shutter speed and aperture. For example, an EV of 1 includes 1 second at f/1.4, 2 seconds at f/2, 4 seconds at f/2.8, and so on. An EV of 7 would similarly include 1/60 second at f/1.4, 1/30 second at f/2, and beyond.

Most hand-held light meters provide readout information in EV, which is a convenient method of determining the SBR of a scene by subtracting the EV for the shadows from the EV for the highlights. This term will be used in the text where modifications to exposures include adjustments to shutter speeds as well as apertures.

Selecting Your Film

Film selection is a matter of personal preference. Normally we try to use faster films, although if we are photographing static scenes using long exposures from a tripod, we may choose to use a slower film. Films of ISO 400 and less have excellent grain and sharpness. I find that I can make 11x or greater enlargements from ISO 400 films without perceptible grain.

More important, is the exposure latitude of the film. The straight-line portion of the characteristic (gamma) curve (this will be discussed briefly below) gives nearly 10 EVs (f-stops) for negative films, but only 5 or 6 EVs for reversal films. In addition, each film has 1 to 1½ EVs of exposure in the compression areas of the toe and shoulder of the curve.

From this point of view, negative films are more forgiving and they can record a much greater range of visual information. Note that the image of the Denver City County Building at the top of this web page was made on transparency film which has attenuated all of the shadow detail in the scene. In this case it was desirable to block out distracting detail.

There is also the decision as to whether to use monochrome or color. Monochrome can be very effective for recording the mood of night photography.

Film Data Sheets

Few manufacturers include film data sheets with the film packaging anymore. However you can go to their web sites and look up the data information for each of their films. (See the Internet Sites section below for the web addresses of the film manufacturers, namely Kodak, Fuji, and Ilford.) Once you get into their web site, look for their film products and select the film of interest. There is typically a button or link to bring up the data sheet for that film in a PDF format so you can print it and put it in your camera bag.

There are three items of immediate interest on these data sheets, these are the granularity, the characteristic curve, and the reciprocity failure (more about reciprocity failure in a later section).

Ilford and Fuji measure granularity by the RMS (root mean square) index where they sample the size of the grains in the longest direction, square this dimension and sum these values. They then divide this sum by the number of samples and take the square root. An RMS value of 4 or 5 is excellent, but grain in the 10 to 15 range is also pretty good. Grain in enlargements becomes more noticeable when the RMS is around 20. Kodak ceased using the RMS a number of years ago, although some of their older film data sheets still show this index.

The Characteristic Curve is shown graphically on the data sheet, but the size of the plot and the lack of sub-tick marks make it difficult to interpolate the exposure values from the logarithmic scale. One must be familiar with skewed nature of the logarithmic scale to make estimates of exposure latitude. It is useful, however, for comparing the exposure ranges and contrastiness of the films under normal development as well as determining if pushing or pulling development will improve the contrast of the image.

Characteristic Curve for Fuji NPH















These examples have been extracted from the Fuji data sheets for illustration. The first one shows the characteristic curves and spectral sensitivity curves for Fuji’s Portrait NPH 400 professional negative color film. Note that the three color layers on the characteristic curves do not produce the same densities in their film layer. That is in part because this is a daylight negative film and it is color corrected so that the blues prevalent in sky and shadows (from the reflected sky) produce the greatest densities in the image. Because these colors are proportionally darker in the negative, they reduce the bluishness in the final print. Also these colors are adjusted for color layer sensitivities of the color print paper. There is not the same separation for the characteristic curves of reversal film.

The spectral density curves show how the intensity of each color layer responds to each color wavelength. Note the Cyan Sensitive layer. This is Fuji’s technique reduce the effect of fluorescent illumination. While the blue-, green-, and red-sensitive layers produce a dye of their complementary color in the negative, the cyan corrective layer is sensitive to cyan and produces a cyan dye in the negative so that its complementary color, red, is produced in the print to neutralize the greenish-cyan color of the fluorescent light.

Going back to the characteristic curve, note the log scale at the base of the chart. These are logarithms taken to the base ten, so that –3.0 is the logarithm of .001, -2.0 is the logarithm of .01, -1.0 the logarithm of .1 and 0.0 is the logarithm of 1. The scale represents light intensities of lux-seconds (which is roughly equivalent to foot-candle-seconds). Note that the straight-line portion of the curves covers more than three decades on the log scale (from –2.5 to +0.5) which is equivalent to a variation in intensity greater than 10 cubed, or 1000.

We are also aware that each increase in EV doubles the exposure so that an increase of 10 EVs is equivalent to increasing the intensity by 1024 (i.e. 2 to the 10th power) which is roughly equivalent to the range of 1000 we estimated above. Thus, the straight-line portion of this curve represents 10 EVs (or 10 f-stops).

The characteristic curve for Fujichrome Provia 100F color reversal film is shown below. Note that there is less color correction and, hence, less separation of the characteristic curves for each color. Note, also, that the curves are reversed so that the lowest exposures produce the darkest (densest) area on the transparency and the brightest exposures leave a very light image. The straight-line portion is less than 5 EV, but the toe and shoulder support 1 to 1½ EV each for a workable range of nearly 7 EV. Characteristic Curve for Fuji 100F















Reciprocity Failure

© 2006  a.c.olson -- Star Trails 2006
© 2006 a.c.olson -- Star Trails Above House. Image was made with a Linhof Technika IV 4x5 camera with a Schneider 150mm lens on Kodak Portra 160 VC film. The photo above shows a 15 minute exposure with aperture between f/8 and f/11. Note the star trails that are visible in the sky above. Each house light was switched on for approximately 4 seconds. Reciprocity failure can be helpful by restricting the blooming of the house lights.

Under normal exposure conditions, a change in aperture would require a similar change in shutter speed to maintain the same exposure. For example, halving the shutter speed would require the aperture area to be doubled. This is called the Reciprocity Law. However, if the exposure is too short, or too long, it is necessary to increase the exposure by an additional amount, either by going to a larger lens opening or by increasing the time the shutter is open. The problem is strictly affected by extreme shutter speeds. While modern films are much improved and have increased the range of shutter speeds that obey the Reciprocity Law, it is still a concern for long exposures.

A rule-of-thumb used by many photographers is to increase the aperture by ½ to one EV if the exposure exceeds one second, by a one to two EV if it exceeds 10 seconds, and increase the exposure by 2 to 3 EVs if the exposure is over 100 seconds. It is important to check the detailed information on exposure correction for long exposures that can be found in the film’s data sheet. In fact, exposure time can usually be extended for hours under the darkest night conditions without causing undue overexposure.

A Brief Outline of Ansel Adams’ Zone System

Ansel Adams created the Zone System to help him determine the “best exposure” and especially to aid him in exposing for a Subject Brightness Range (SBR) that best matched the contrast that he visualized for the scene. He initially used a 7-zone system for his black and white work, but as film material improved and the straight-line portion of the characteristic curve became longer, he advanced to an 11-zone system. Each zone is an EV greater than the preceding one, and the amount of incoming light is doubled from one value to the next. The following table uses his description of the lighting conditions the photographer would encounter with the 11-zone system.

Print Value Range Zone Description of Print Tone
Low Values O Total black in print. No useful density in the negative other than film base plus fog.
... I Effective threshold. First step above complete black in print, with slight tonality but no texture.
... II First suggestion of texture. Deep tonalities, representing darkest part of image where some slight detail is required.
... III Average dark materials and low values showing adequate texture.
Middle Values IV Average dark foliage, dark stone, or landscape shadow. Normal shadow value for Caucasian skin in sunlight.
... V Middle gray (18-percent reflectance). Clear north sky near sea level as rendered by panchromatic film, dark skin, gray stone, average weather wood.
... VI Average Caucasian skin value in sunlight or artificial light. Light stone, shadows on snow or light sand in sunlit landscapes.
High Values VII Very light skin, light-gray objects; average snow with acute sidelighting.
... VIII Whites with texture and delicate values; textured snow; highlights on Caucasian skin.
... IX White without texture approaching pure white, thus comparable to Zone I in its slight tonality without true texture. Snow in flat sunlight.
... X Pure white of the printing-paper base; specular glare or light sources in the picture area.

Adams has produced his own version of the characteristic curve by mapping these zones onto the characteristic curve as shown below instead of representing the exposures in lux-seconds. He did this by converting the scale from base-10 logarithms to base-2 logarithms.

In addition to converting the scale from base ten to base two, Adams has shifted the origin of the x-axis to coincide with the speed point of the characteristic curve. Note that he shows the increase in density for each EV as a shaded wedge. The use of the term exposure units is to designate the relative increase in exposure for each zone.

Example of a Characteristic Curve The accompanying figure is an example of a characteristic curve that represents the relationship between film exposure and negative density for B&W negative film. Each subdivision of the horizontal axis represents a doubling of exposure (an increase of one EV) as you move from left to right. The ISO film speed is defined to be the exposure to produce a negative density of 0.10 units above the film base plus fog density. The toe of the curve is the region where the negative densities are compressed in image areas receiving very low exposure.

The shoulder of the curve is where the densities are compressed for the highlight regions. The straight-line section represents the middle gray regions that have the greatest separation of density.

Metering Techniques

For those using cameras with auto exposure, excellent results can be obtained, especially with recent cameras having matrix metering. These cameras meter the different areas of the scene and then interpret the positioning of the various highs, lows, and mid-tones to compute a satisfactory exposure. We may, however, have a different interpretation in mind concerning how we represent the highlights and shadows. These cameras also have exposure compensation settings. The reader should consider the points below when exposing the image and necessary compensation adjustments to create the image as invisioned.

For the purpose of exposure simplification in night photography, there are three zones that are of importance depending upon the goal of the photographer. The first zone is either Zone II or Zone III where the photographer decides how much detail or texture he wishes to record in the darkest shadow areas. The middle zone, Zone V is important because this is the zone to which the light meters are calibrated and to which the photographer is most likely to envision matching 18% gray.

Finally, Zone VIII may be important if the photographer is concerned about maintaining texture or detail in the brightest parts of the scene. In urban or indoor settings where there are artificial light sources appearing in the scene, their specular nature in Zone X will likely make it unnecessary to be concerned about this zone at all. Other zones may be of use for metering depending on such factors as skin color, specular highlights, or dark shadows. If the SBR is greater than the characteristic curve, compromises must be made. Adjustments such as push- or pull-processing may be used to adjust the film's SBR, but this is beyond the scope of this booklet.

Normally for color or black and white negative films, the best exposures will be to meter for sufficient detail in the shadowed areas (usually Zone II, but sometimes Zone III) and then subtract 3 EVs for Zone II or 2 EVs for shadow detail in Zone III. This will darken the exposure for the shadow from the metered 18%-gray to the correct value for the shadow zone. For color transparency film the adjustment would be a decrease in exposure of 2 EVs.

Now check the highlights for Zone VIII. If the highlights fall below into the middle range, some compromises may be made. Consider increasing the exposure to improve the shadow detail, but be careful that the specular highlights may blow out. This problem is not too likely in night photography since the brightest spots in the image are the point light sources and the remainder of the scene usually falls several EV below, well within the straight line portion of the characteristic curve.

In the case of nighttime photography, often the subject is brightly illuminated, for example, the moon. We do not want to overexpose and blow out the highlights of the subject but instead wish to retain the detail in the image of the full moon. In this case, expose for the zone that is representative of the subject matter and add or subtract an EV or so of exposure to adjust the terrestial subjects into the desired Zone. An example of this might be to meter the full moon which would give a reading in Zone V. But we may be willing to accept the moon appearing a little brighter to better record the surrounding scene by moving its exposure into Zone VI or VII, still retaining some impression of detail. For the matrix metering systems we would add compensation to overexpose by an extra EV.

© 2006  a.c.olson -- Moon Over the Mall 2002
© 2002 a.c.olson -- Moon Over the Mall. Fuji NPH 400 film using a Nikon F100 camera with a Tamron 28-300mm zoom lens. In the example above the exposure was metered to place the moon in Zone V. In this case, if we had moved the exposure for the moon into Zone VI or higher, the Lincoln Memorial highlights would have been blown out. Note that there is almost no shadow detail in the areas of the trees.

For night photography we may not care, or even prefer, that there is no detail in the shadow areas so then it is more effective to meter on the brightest subject to ensure detail and let the shadows take care of themselves. Existing light photography is a wonderful technique for suppressing undesired elements that would otherwise ruin the composition if they were photographed in full daylight. These judgements depend on the overall brightness and light distribution of the scene.

For transparencies the situation is a little different. First of all, the characteristic curve for reversal films is 3 to 5 EVs shorter so the SBR becomes compressed. This means that more of the exposure will take place on the toe and the shoulder of the characteristic curve where the density changes are further compressed. When using transparency films, it is more important to meter for the highlights and increase the exposure by approximately 2 EVs. This corrects the highlight exposure to Zone VII and will prevent the highlights from becoming overexposed. Note the loss of shadow detail in the image of the transparency on the right. This image was made in 1990 on Kodak Ektachrome with a Nikon F2 and Vivitar 35-85mm Varifocal lens. The image was made with a slight underexposure to produce better color saturation.

A spot meter is most useful for checking the illumination on the highlights of the brightest subject. Because the meter reading assumes that the bright area will exposed for Zone V, normally you will add 3 EVs to move its exposure into Zone VIII. A spot meter can also be used to compare readings of other key zones to determine if the exposures fall into the zones as you visualized them to achieve your intended tonalities. It should be noted that a camera’s spot meter can be used for these readings, but a handheld digital spot meter is much easier to use. Most handheld digital spot meters have a memory so you can evaluate the exposure range from shadow (Zone II) to highlight (Zone VIII) and see how the middle gray reading fits into this range.

Ignore specular highlights, especially from point light sources, because they only overexpose a tiny area on the negative or transparency. Once a pure white is reached during the exposure, overexposure is irrelevant. It should be noted, however, that the longer the exposure, a point light source will “bloom” and spread out on the negative. This is rarely objectionable. You will most likely also get a “starburst effect” caused by the diffraction of the diaphragm, see the section below on Refraction/Diffraction.

All of this said, there are advantages to using the modern matrix metering systems. I have found that the matrix metering on the Nikon F-100 produces nearly the same exposure as I would compute using a handheld spot meter. There are times, however, when I want to check the SBR to determine if there are compromises to be made in evaluating the shadow detail in comparison to strong highlights. With the F-100 I usually rely on the matrix metering system, but with large format and earlier 35mm cameras I always use the spot meter to determine the correct exposures.

In situations where I am shooting sunsets or moonrises in the twilight I usually meter from a dark area of the sky (not too far from the sun if it is still above the horizon) and use that as my Zone V value. I will continue to use that exposure as the sky gets darker because I do not want to overexpose objects brightly lit in artificial illumination. I also use the spot meter to monitor the subject to guarantee that it will not be overexposed so it will retain the desired semblance of texture and detail as the lighting changes.

Balancing Ambient Light with Twilight

© 2006  a.c.olson -- Two Minute Exposure 2006
© 2006  a.c.olson -- Four Minute Exposure 2006
© 2006  a.c.olson -- Ten Minute Exposure 2006
© 2006 a.c.olson -- Twilight at the Mountain House. Images were made with a Bronica SQA 6x6 camera with a Zenzanon 200mm lens on Kodak Ultracolor 160 film with the aperture midway between f/8 and f/11.
The upper photo is the 2 minute exposure, the middle photo is the 4 minute exposure and the last photo is the 10 minute exposure. Note the difference in the balance of the ambient light against the twilit sky.

There exists a time during Nautical Twilight when the light in the sky balances well with the artificial lighting on the ground. I have found that the best time to make photos of scenes that will include the ambient, artificial lighting as well as showing good sky color occurs about 40 minutes after official sundown but before the end of Nautical Twilight (or earlier than 40 minutes before sunrise). The time of official sundown can be obtained by visiting the site of the US Naval Observatory, http://www.usno.navy.mil/, to look up the times for sunrise or for sunset.

To make a photo of an artifically lit scene and get the best color from a twilight sky I set my equipment up so that I am prepared to start photographing at around 40 minutes after sunset. Earlier than that and the differential between sky and terrestial lighting is usually so great that either the sky is blown out or the ground lights are marginally visible.

I work primarily with ISO 160 color film. The aperature is set midway between f/8 and f/11. Then I make the first exposure for 2 minutes. The light meter may suggest only 20 or 30 seconds, but quadrupling the exposure seems to accommodate reciprocity failure quite well. It doesn't hurt to overexpose a little. For night photography, the film will be more forgiving for overexposure than for underexposure.

Immediately following the 2 minute exposure I follow it with a 4 minute exposure, and lastly a 10 minute exposure. By then it is dark. The light has faded fast. I use the longer exposures to counter reciprocity failure and also account for the fact that it has become much darker than the preceding exposure. There may be slight delays between the exposures while an assistant is resetting the interior and exterior lights. This exposes the subject with a balanced ambient lighting.

Any light where the source is exposed to the camera should be no more than about 3 seconds in duration (One-thousand-one, one-thousand-two, one-thousand-three). In some cases 2 seconds may be better if that light seems much brighter than the rest. If you are photographing a building you can leave the lights on the full time if the light source is not visible. This helps illuminate the surrounding environment with the light spill. Side lighting does not overwhelm the exposure like direct lighting is apt to do.

Refraction/Diffraction

You may wonder why a discussion of diffraction in a guide about existing-light photography. The reason is because at every workshop someone asks why there is a starburst around point light sources. This is an attempt to briefly describe the characteristics of light and why it causes the starburst effect. Diffraction is always present, but seldom appears visually except when the point source is much stronger than the existing ambient light.

There are two ways that light is caused to be bent. One is refraction where the light passes across the surface between transmitting media of two different densities and the other is diffraction where light bends when it passes across the edge of an object.

Refraction occurs in a lens as light, moving through air, enters the glass material where it bends toward the perpendicular to the surface. When it exits the denser material, it bends away from the perpendicular. This effect can be seen in prisms and is a very important property of carefully designed lenses.

Diffraction, on the other hand, not only bends the light, but the light is usually scattered some because of the microscopic imperfections in the object’s edge. Imagine a focused light beam shining on a wall and hold a razor blade perpendicular to the beam of light. As you move the razor blade farther from the wall, the shadow of the razor blade becomes more diffuse. Even close to the wall, there will be a fringe of light around the shadow. There are also interference patterns caused by reinforcement or cancellation as the rays travel different distances and their wave trains arrive at the same point but in different phase.

A lens opening of f/8 is considered the optimal aperture for a normal 50mm lens. As apertures become smaller, diffraction becomes more pronounced and begins to degrade the image significantly (although depth of field will increase). This is a physical limitation and is caused by reducing the ratio of the area of the aperture (that affects refraction) to the aperture circumference (that affects diffraction). Diffraction begins degrading the image at apertures smaller than f/8 for a 50mm lens, but diffraction does not achieve the same effect for a longer focal length lens because the physical size of the f/8 aperture is much larger. For example, the critical aperture for a 200mm lens would be f/22 and smaller.

The effect of diffraction is noticeable when photographing point light sources in a dark background, or even just very bright light sources. Most obvious is the starburst effect caused by diffraction. This may occur even at the larger apertures because of the high contrast between the light source and the rest of the scene. The starburst is caused by the fact that the aperture is not perfectly circular, but is made up of several blades, each having a straight or nearly straight edge. Thus, at the corners of the aperture, the light that is bent and scattered by one blade gets reinforced by the light that is bent and scattered by the adjacent blade to increase the exposure in that area and form the point of the star.

The smaller the aperture, the more accentuated the starburst will become. A special filter is not necessary to create the starburst effect, selecting a smaller aperture will accomplish the same result. In high contrast situations, you may not be able to eliminate the starburst even when using the widest aperture available on the lens.

Specular Highlights

Specular highlights are those bright spots in a scene such as reflections off glass, chrome, edges of painted metal, water, and they include light bulbs, fixtures, etc., that exceed the contrast range of the film. Their brightness exceeds Zone X and they display no texture or detail. In night photography, specular light usually originates from artificial light sources. For example, the street lights in a street scene. They may also occur as reflections from shop windows, from the shiny finish of a car, or similar objects. They are rarely objectionable as long as they take up only a small area in the image, usually appearing as a small, bright spot. Only if they are very large, may we wish to expose them in Zone VIII or IX to emphasize some texture.

Photographing Scenes with a Rising or Setting Moon (or Sun)

The US Naval Observatory site, http://aa.usno.navy.mil/, provides data for determining the times and locations of the sun and the moon as well as their position at any time. This is useful not only for determining when these events will occur, but also locating a position to photograph other ground subjects to be included in the scene. The following instructions lead you through the steps to obtain this information from the observatory site.

Getting Sun and Moon Data:

After entering the home page, click on Data Services. Then select Complete Sun and Moon Data for One Day. The next screen provides a choice of forms for you to enter your geographic location and date of interest. From this information the site will display a table as shown in the following example:

© 2006  a.c.olson -- Moonrise Over the Sangre de Cristos 2006
© 2006 a.c.olson -- Moonrise Over the Sangre de Cristos. Image was made with a Bronica SQA 6x6 camera with a Zenzanon 200mm lens on Kodak Portra 160 VC film.
The view is looking at the moon rise over the Sangre de Cristo Range from the western side of the San Luis Valley.
The following information is provided for Pagosa Springs, Archuleta County, Colorado (longitude W107.0, latitude N37.3):
Wednesday
23 February 2005 Mountain Standard Time

SUN
Begin civil twilight 6:21 a.m.
Sunrise 6:47 a.m.
Sun transit 12:21 p.m.
Sunset 5:56 p.m.
End civil twilight 6:23 p.m.

MOON
Moonrise 4:35 p.m. on preceding day
Moon transit 11:48 p.m. on preceding day
Moonset 6:51 a.m.
Moonrise 5:37 p.m.
Moonset 7:16 a.m. on following day
Full Moon on 23 February 2005 at 9:54 p.m. Mountain Standard Time.

Sunrise and sunset, as well as moonrise and moonset, are the times when the entire disc is immediately below the horizon. Civil Twilight is the time that the sun is below the horizon, but the ambient light is sufficient to carry on normal outdoor activities. There is also Nautical Twilight (such data is not provided on this internet site) that occurs for approximately 30 minutes before civil twilight in the morning and for 30 minutes after civil twilight in the evening. During nautical twilight it is still possible to see and make out objects, but the lighting is not suitable for carrying on normal outdoor activities.

It should be noted that long exposures during nautical twilight can bring out some very striking colors, shading through light pinks to deep blues, in what would appear to the eye to be a very bland sky. Long exposures are also affected by the lighting differences on ground objects and will change the emphasis on these subjects as well.

The light in the sky before sunrise usually has the best color so it is important to be ready to shoot an hour before (at the start of nautical twilight) when the color begins to appear in the sky. Longer shutter speeds bring out a lot of detail that is not apparent to the naked eye.

It should also be noted here that if you are attempting to shoot a moonrise over some subject of interest, the best day, weather permitting, is when the moonrise occurs near or a little after sunset. The twilight gives a better balance for contrast between the moon and the sky as well as illuminated objects on the ground. If the sky is too bright (i.e. when the sun is above the horizon), the moon’s image will be very faint. When the sky becomes too dark (i.e., between the end of nautical twilight in the evening to the beginning of nautical twilight in the morning), the moon will be too bright with respect to the surrounding environment and all texture will be lost.

Allow 10 to 15 minutes for the moon to clear the horizon (i.e., rise above the buildings, trees, etc.) if you are in the low country and as much as 50 minutes to clear the mountains. Because the moon moves its diameter every 6 minutes, long exposures cause the moon to appear elongated. During a 30 second exposure the moon will move 1/12 its diameter, so shoot with a wider aperture to allow faster shutter speeds.

Not only are full moonrises wonderful photographic opportunities, but full moonsets can also be photographed the hour of twilight before sunrise. In this case you want the moon be above the horizon until the sun rises. Not many photographers seize this opportunity because it requires rising sufficiently early to allow for the travel time needed to reach the chosen location an hour before sunrise. The advantage of photographing moonsets is that early in the day there are few distractions to get in the way of your photography.

The moon will appear round even at 99 or 98 percent illumination which it is the day before or the day after the full moon. Sometimes the moon is in better synchronization with twilight at these times.

Full moons and crescent (illuminated less than 50 %) moons are the most photogenic. Crescent moons usually appear later in the evening when the sky is darker. That means that its relative illumination will most likely fall into Zone XI or X where there will be no surface texture in the image. But in this case we are usually more concerned about simply capturing the shape than capturing texture and detail of the moon.

Crescent moons are also visible during daytime hours, but will be too faint in the bright light to make a very impressionable image. The best time to photograph them is when they are appearing in the west shortly after sunset.

Let us now address the question of where to position yourself to place the moon or sun near or behind a terrestrial subject. Back on the Data Services page, select Altitude and Azimuth of the Sun or Moon During One Day. This will again bring up a choice of forms specifying your geographic location and the date of interest. For this chart you must also select a radio button for either sun or moon data. The following table will be printed:

PAGOSA SPRINGS, COLORADO
W107 01, N37 16
Altitude and Azimuth of the Moon
Feb 23, 2005
Mountain Standard Time

Time hh:mm Altitude (degrees) Azimuth degrees
(E of N)
Fraction Illuminated
00:00 69.7 188.0 0.99
00:10 69.3 194.7 0.99
... ... ... ...
07:40 -9.6 297.7 1.00
07:50 -11.3 299.3 1.00
... ... ... ... [The Naval Observatory leaves a gap here.]
16:40 -10.8 63.7 1.00
16:50 -9.1 65.3 1.00
... ... ... ...
17:30 -2.0 71.5 1.00
17:40 0.3 73.0 1.00
17:50 1.9 74.5 1.00
18:00 3.7 76.0 1.00
18:10 5.5 77.4 1.00
18:20 7.3 78.9 1.00
18:30 9.2 80.3 1.00
18:40 11.1 81.8 1.00
18:50 12.9 83.2 1.00
19:00 14.8 84.6 1.00
19:10 16.7 86.1 1.00
... ... ... ...


Note: Use care when reading time from this table because this table usually stays in Standard Time while the first table is converted to Daylight Time during the summer months.

This table was selected to note the position of the moon every ten minutes. The altitude is measured by the angle of the moon above our horizon. When the altitude is negative, the moon is below the horizon. The Naval Observatory leaves a gap between 7:50 and 16:40 because the moon is below the horizon so this information would be of no use. The gaps denoted by the ellipses contained data that was not relevant and was removed by the author to conserve space. The lines from 18:00 to 19:00 show the relevant information where the moon would be visible during twilight.

The azimuth is the direction to look to see the moon and this angle is measured clockwise from due north. If you are attempting to photograph the moon rising over a predetermined subject you can estimate the direction of the moon to position yourself or you can be more methodical. If you wish to be more accurate then obtain some large scale maps or charts. The USGS 7 ½ minute quadrangles (1:24000 scale) are excellent sources or, if necessary, the 15 minute quadrangle (1:48000) maps. The USGS also produces topographic map sheets of counties or parts of counties that are mapped to a scale of 1:50000. Nautical charts and tourist maps may also be useful.

The most accurate procedure is to locate the subject on a topographic map. Select an azimuth from the table above. Note that for the first hour of moonrise the direction changes by over seven degrees. Assume that we want to begin photographing when the moon reaches 80 degrees azimuth. Using a protractor, draw a line through the subject that is 80 degrees from due north. Extend this line in the opposite direction westward at 260 degrees for your shooting location. You can now select a safe location where there are no obstructions, distracting foregrounds, dangerous traffic situations, etc.

Photographing Fireworks and Lightning

There is no good way to calculate the exposure for fireworks and lightning, or for the lights of moving traffic. This is similar to painting with light where the light source is moved across the subject and exposes each grain or pixel based on the intensity and the total duration that the light illuminates that part of the subject. It is not the intention to cover "light painting" in this guide, but the WEB site, http://www.TheNocturnes.com contains many fine examples (and many tacky ones too) of light painting as well as some tips in their forum on how to achieve these effects.

When painting with light, it matters little how long the shutter is open because the exposure is determined by the moving light source. In the case of fireworks it is the same. There may be some overlaps that will cause certain portions of the image to “blow out.” But normally you can leave the shutter open for extended exposures by setting the aperture to the film's ISO index. According to Kodak’s workshop book, the following table should help:

ISO 25 40 50-60 100-125 160-200 320-400 800-1000 1600
Fireworks-aerial f/4 f/5.6 f/8 f/11 f/16 f/22 f/32 f/32
Lightning f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22 f/32

If there is a subject that you also wish to work into the image, for example fireworks at the Washington Monument, use the above f-stop based on the ISO of your film, take an exposure reading of the Monument, and then adjust the time the shutter is open. In this case you will want to select a low ISO film to allow the shutter to remain open long enough to capture the fireworks. This may require a compromise between exposing the fireworks correctly and exposing a subject on the ground.

Using Graduated Neutral Density Filters

Graduated neutral density filters are invaluable for balancing the exposure of an early morning twilight sky against a darker foreground. For example, when photographing a predawn sunrise over the ocean, the sky may be two or more EVs brighter than the water. A graduated neutral density filter can be fit over the lens and adjusted so that the dark half of the filter is above the horizon and the clear half allows full exposure of the water. This will keep the sky from being overexposed while retaining enough exposure to capture the details in the foreground. Because the graduated filter does not change abruptly, it can be used for irregular horizons and in other situations as well.

Graduated neutral density filters come in several gradations. The Cokin filters are made of acrylic material and cost about $15. They are available in 1, 2, and 3 EV reductions and are designated 1, 2, and 3. More expensive filters, made of optical glass, cost around $70 or $80 and use the designations: .3 for the 1 EV, .6 for 2 EVs, and .9 for 3 EVs. This designation is used because .3 is the logarithm to the base 10 of the value 2, .6 is the logarithm of the value 4 and .9 the logarithm of 8. Hence each increment of .3 results in an additional EV increase.

Using Fill Flash

Fill flash is often used to illuminate shadow areas so that the details in the shadow will record on film or chip. Normally, the flash exposure should be 1.3 to 1.7 EVs less than the exposure for ambient light to prevent it from appearing to be lit artificially. For most of the dedicated flash units, this amounts to a reduction of exposure relative to the camera’s through-the-lens metering during automatic exposure. For those flash units that are not dedicated, first determine the exposure for the camera and then set the flash to an intensity that is 1½ EVs less.

Internet Sites

http://http://www.usno.navy.mil/
http://www.TheNocturnes.com
http://www.photo-artiste.com/night.html
http://www.ilford.com -- Currently Ilford/Harmon no longer supplies film data on their WEB site.
http://www.fujifilm.com/products/professional_films/index.html -- Professional films
http://www.fujifilm.com/products/consumer_film/superia_100.html -- Consumer films
http://www.kodak.com/global/en/professional/products/prodSupportIndex.jhtml -- Professional films
http://www.kodak.com/eknec/PageQuerier.jhtml?pq-path=9/7010/6994&pq-locale=en_US -- Consumer films

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References

Each of the following books has been found to be a useful reference. While there is a general overlap of material covered, each author has a different approach and provides many useful tips.

Adams, Ansel Easton, 2003, The Camera , New York, N.Y., Little, Brown and Company, 203 pp.

Birnbaum, Hubert C., 1996, The Kodak Workshop Series: Existing-Light Photography , Rochester, N.Y., Silver Pixel Press, 88 pp.

Carucci, John, 1995, Capturing the Night with Your Camera: How to Take Great Photographs After Dark , New York, N.Y., Amphoto Books, 144 pp.

Frost, Lee, 1999, The Complete Guide to Night & Low-Light Photography , New York, N.Y., Amphoto Books, 192 pp.

Hicks, Roger and Schultz, Frances, 1999, Perfect Exposure from Theory to Practice , New York, N.Y., Amphoto Books, 192 pp.

Peterson, Bryon, 1990, Understanding Exposure , New York, N.Y., Amphoto Books, 144 pp.

Schaefer, John P., 1999 (Rev. ed.), The Ansel Adams Guide, Book 1 -- Basic Techniques of Photography, New York, N.Y., Little, Brown and Company, 418 pp.





Technical Guides

Tripod Guide
Multiple Exposure Guide
Infrared Guide
Existing-Light Guide

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Al Olson
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