THE ALL-SKY CIRCLE

THE SKY IS NOT THE LIMIT!

This first installment will focus on how to photograph an all-sky on location - from the photographer's viewpoint. An all-sky, as described hereafter, is a vertical, six-part wide-angle panorama that covers the entire dome when projected  Such subjects as basic equipment, setting up, composition, light metering, films and filters will be discussed.

BASIC EQUIPMENT

The following checklist outlines the minimum equipment required for photographing a successful all-sky. There are several ways to do this using different equipment on location, but the method we'll describe is both simple and inexpensive.
1) One 35 mm SLR camera
2) Either a 15 mm, 16 mm or 17 mm standard wide-angle lens
3) A tripod with horizontal and vertical calibration
4) Light  meter for cameras without  one
5) A built-in or separate level for the tripod
6) Cable release. Stopwatch.
7) Notebook and pen to record one's settings and other information

To photograph an all-sky using 35 mm slide film, one requires a single 35 mm SLR camera, preferably with its own light meter, although a hand-held meter will also suffice in this respect. Besides the camera body, a wide-angle lens of either 15 mm, 16 mm, or 17 mm focal length is recommended. These lenses are available for almost any standard SLR such as Canon, Nikon, Olympus, Minolta, Pentax, etc.. A tripod with a head that allows the camera to be tipped sideways into the vertical position, and with both vertical and horizontal calibration is necessary. The horizontal or azimuth circle  should be divided into six equal segments of 60° each. Mark one of these segments with an arrow to indicate the central frame of the all-sky, your starting point. The vertical altitude circle should be marked off in increments of 5° minimum (we use 3° increments), indicating angles from 90° (horizon) to 0° (zenith). The 45° and 30° marks are especially important, as most all-skies can be shot at or between these angles. A built-in or separate level for leveling the tripod is a necessity.

SETTING UP

First one has to position the camera in a location that will look the most effective and representative of the scene to be projected onto the dome. It is important to distance the camera from objects such as trees, buildings, boulders or anything that might appear disproportionately large if photographed too close to a wide-angle lens. Because six frames will be taken in succession rotated around 360°, the major point of interest should be in frame one. Align the first calibrated mark on the tripod's horizontal axis to this point. Before you begin leveling, look through the camera and inspect the future all-sky. Now level the tripod so that as the camera is rotated around the 360°, the horizon in the frames will remain consistently level. This can be done by using the tripod's bubble level, or by using a simple line level to bring each tripod leg into perfect level. Once this leveling is done, align the bottom of the camera body so that it is parallel with the tilt-pan head platform. This is to  insure that once one has tilted the camera vertically, the actual angle of the film plane will be the same as that indicated on the tripod's vertical calibration. The "standard" vertical tilt on an all-sky used to be 45°, although there are many circumstances in which a 35° or a 30° tilt are much preferred. If the 45° tilt is used, the tripod usually has to be dropped as close to the ground as possible in order to include the foreground. However, at this angle vertical objects of any height will not align correctly from frame to frame when projected. Using a 30° or 35° tilt seems to correct this type of vertical criss-cross misalignment. Remember when you're choosing the degree of tilt , that the further back the camera is tilted, the more prominent scalloping becomes at the edges of each frame. Before fixing the vertical tilt, determine the correct light exposure for the scene. (See LIGHT METERING)

Right from the beginning, establish a system for yourself that will have you taking your sequence of six frames, either going in a clockwise or a counter-clockwise direction. Once this direction is established, continue to follow this pattern in your all-skies thereafter. Because everything in the frame should be in sharp focus, use an f/stop that will achieve this. We normally set our aperture at f/11 or f/16, with the lens focussed at Infinity. To minimize camera vibration and for obtaining longer than usual exposures, use a cable release. A stopwatch is very handy for timing long exposures. So once the center of the first frame is fixed, the tripod is leveled horizontally, the camera is properly fixed to the tilt-pan head, the correct light exposure is determined, and the appropriate vertical angle is set, the all-sky may now be taken.

COMPOSITION

As mentioned, the most important detail should be in the center of the first frame. A building split between two frames can pose tedious alignment work in the theatre. Ideally - in an outdoor situation under an open sky - the subject would not come up farther than one-third of the frame. Many subjects can go half-way up in the frame; irregular formations, such as mountains, may look normal, while straight-line objects, such as buildings, will appear to lean and curve over the audience when projected. Canopies and indoor all-skies are exempt from this rule. When figures exceed the half-way mark, go ahead if you have the film to experiment. Seeing the actual results on your dome (if you've never seen it before) is worth one all-sky. Besides, when you dupe, the slides may be pulled down far enough in the frame to make the difference.

LIGHT METERING

The light under which you photograph can create a dramatic variation in how an image appears  when projected Of course, we would all prefer the ideal situation where the main subject is well illuminated and the sun can be positioned behind an object. But this isn't as important as deciding what really needs to be seen clearly. If one can determine that, there's usually a way to achieve it. Once that focal point is established, all other details become relational to it.
 For instance:
1) If the subject is not the sky, carefully avoid the sky when taking the light readings.
2) Meter the main subject. If there are strong variations in light, consider if an averaged reading will work, or if an average will obscure important details.
3) Meter the 360°. If there's a difference of 4 f/stops or more, the darker areas may be lost visually. Would a compromise with the main subject be acceptable?
4) Set the camera aperture and shutter speed manually, so that neither can vary during the shoot. Left on automatic, the results will be six distinctly non-blended frames.
5) Shoot the all-sky to your best calculation, and then consider a bracketed set, especially in a far-off location. Do the six-part sequence as quickly as possible, as outdoor light conditions can change rapidly.
6) If you don't have enough film to bracket, shoot at "normal." The exposure can be altered during duping.
7) About the sun staring straight into the lens - block it with a hat or hand and shoot; there are ways of dealing with that later!

FILMS

Having used about every slide film on the market, here are some recommendations. If possible, use professional film and an ISO of 25, 50, 64 OR 100; the results during slide duping are worth it. While Kodachrome, and regular Ektachrome and Agfachrome provide true and beautiful colors, there is some loss of color during projection. And since all-sky wash-out is a major problem, take what measures are available. Fujichrome will punch up the colors, but Velvia and Ektachrome will saturate them. These emulsions were developed for hi-gloss commercial photographers who rely on heavy color for impact. They're perfect for planetarium use. Not only will Velvia and Ektachrome enliven and saturate colors, but on that inevitable day when you arrive on location under leaden skies, it will put green back in the grass and a bit of "sunshine" where it wasn't. It will not perform miracles, but it's the next best choice. A word of caution. Velvia is a high contrast film; dark shadows will record darker, and hot spots spread farther than your eye can detect. Ektachrome 64-X and Agfachrome RS-Plus have been designed to compete with Velvia. Give them all a try and don't forget to pick up Tungsten film for your indoor all-skies, where appropriate.

FILTERS

Filters can solve many obnoxious problems. Here's a fundamental set to carry.
Polarizing Filter: This one's especially useful when you don't have Velvia. It will saturate colors, particularly the blue sky. Remember to rotate the filter for every frame. DO NOT use a polarizer with Velvia; dark colors and shadows turn black, detail is lost.
+2 Graduated Blue Filter: Because metering is generally done for subject matter, skies end up almost white, which further complicates things during projection. The high level of incidental light bouncing around on the dome will wash out the subject matter. This filter addresses both problems. Metering should not include the filter.
+1 Orange: Useful for stone (archaeoastronomy), orange sharpens details and saturates stone colors especially under gray skies. You may need to consider a kodalith mask for the sky, if its color becomes objectionable.
+2 Graduated Neutral Density: Check this one out indoors if there are glaring overhead spotlights. Ceiling details will probably be lost if this filter is used. Do not include the spotlights or filter in metering.
+2 or +4 Full Neutral Density: Going to a location infested with tourists? This filter will "remove" them provided that they are moving along and not standing in one place. By using the filter and a high aperture such as f/16, the shutter speed ends up at 1-minute or longer.
 
 

The Sky Is Not The Limit!  Part Two

The first instalment of this column outlined a basic procedure for photographing an outdoor all-sky.  We will now continue by detailing the procedures for doing this inside an enclosed space.  Please review the previous article on outdoor all-skies for incidental details that are common to photographing interiors and exteriors.

BASIC EQUIPMENT

All equipment for doing interior all-skies remains as for an exterior all-sky, except for the possible inclusion of an extra light source(s).
1)  One 35mm SLR camera with manual controls.
2)  Either a 15mm, 16mm or 17mm standard wide angle lens. 3)  A tripod with horizontal and vertical calibration.  The azimuth circle should be divided into six 60° segments.  The altitude circle should be marked off in 5° increments indicating angles from 90° (horizon) to 0° (zenith).  Mark one of these segments with an arrow to indicate your starting frame.
4)  A built-in or separate level for the tripod.
5)  Light meter for cameras without one.
6)  Cable release.  Stopwatch.
7)  Flash unit(s).
8)  Flashlight.
9)  Notebook and pen to record settings and other information.

The procedure for interior all-sky photography requires the same precision and attention to detail as does the exterior form.

SETTING UP

With an interior, some new variables are introduced into the equation.
1)  Level the tripod.
2)  Align the camera body with the tilt-pan head platform so that when the camera is tilted sideways and vertically, the film plane angle will be the same as is indicated by the altitude circle markings. Use a 30° or 35° tilt, especially where there are straight vertical or horizontal lines.  It has been found from experience that using a 45° vertical tilt will produce "criss crossing" alignment problems in the upper portions of adjacent frames.  A 30° vertical tilt  corrects such straight line distortions most effectively.  Set the aperture on manual, using f/11 or f/16 when possible with the lens focused at Infinity unless the feature being photographed is closer than 5 feet. Usually a long time exposure will be required. Shutter speed should also be manually controlled. Use a cable release. Inside a dark interior, a flashlight will be necessary to check readings, to align angular positions accurately, and to reference a time piece during long exposures. 
3)  Center the most important feature in the first frame. Align the arrow on the azimuth circle to this point.  Be sure you are far enough away from any features that will appear disproportionately large or distorted when photographed through a wide angle lens. Each of the six frames will be rotated around the 360° azimuth circle in 60° increments.
4)  Determine the most appropriate light exposure for the situation. If there are extremes in light values, a flashlight or lamp (with or without gels) can be handy in highlighting particular details by "painting" them with light. A hand held fill-in flash can also be used to bring out details in darker areas of an interior.
5)  Take your pictures! 

COMPOSITION

There is more to creating an effective panoramic scenario than simply putting the camera and tripod anywhere that the major features of an enclosure can be seen.  There is also a very definite qualitative aspect related to the atmosphere (mood) that the imaging is helping to convey that is as important as the informational part of the photography. The mere data of a location doesn't necessarily transmit all the factors that are inherently implicit in a space. Precision in the mechanical details must be complemented by an artistic imagination that knows how to translate not only the physical properties, but also the unique feeling that comes through from each spatial matrix.  If a location is dark and mysterious, the mystery should be felt by those viewing the projected scenario. If a situation is awe-inspiring, the photographer must in some way arrange the sequence of images so that awe is felt by the viewer.  Conscious attention to this aspect of photography is what transforms mere recording of details into creative interactive art.  A conscious photograph not only unfolds the details of a space but also the knowledge of the time scale that relates to it. Through such effort the intelligence of the viewer is aroused.

LIGHT METERING

When measuring the light intensity inside an enclosure, the lighting problems are different, although no less tricky than those found in an exterior all-sky.  Normally, one doesn't have to contend with a glaring solar disk in several frames, but quite often artificial lighting can create similar problems.  It is critical to exclude bare light sources while metering. Take the exposure off areas you wish to be seen,  and forget the rest. A hand held spot-meter with a narrowed reading angle makes this a simple procedure.
Reciprocity failure, due to a change in light sensitivity of the dyes in a color film, can produce shifts away from normal color and contrast values, especially with longer exposures and small apertures such as f/11 or f/16. To compensate for such shifts, double the time. For example,  if the exposure meter reads 1 minute at f/11, expose the frame for 2 minutes (1 stop overexposure) or even more. Bracketing is a must under such conditions.
If there is ample lighting in an interior, set the aperture and shutter speed for the details that will be the focus of attention.  If not, use fill-in flash to bring out details that would otherwise be lost.
For other tips on exposure, refer to the article on outdoor all-skies.

FILM AND FILTERS

With interiors, artificial or mixed lighting creates the necessity for selecting films and/or filters that will render the situation in the most complimentary light (pun intended).  Using daylight film, tungsten lighting gives a decidedly yellowish cast to anything that it illuminates. The remedy for this is to use a blue 80A correction filter or to change to tungsten films such as Ektachrome 64-T or Fujichrome 64 tungsten. Quite often one can encounter a mixture of tungsten and fluorescent lighting. This is a tricky situation, but a viable solution is to use tungsten film with a fluorescent (magenta) filter. These filters come in different strengths. With the increased use of fluorescent lights, medium to heavy filters get the most use. By the way, "daylight balanced" fluorescent tubes produce just as pronounced a green cast on film as do any other tubes.  However, if the effect sought is enhanced by off-coloration, let your imagination dictate the film, filters and lighting.

CORRECTIONS TO ALL-SKIES

 The followng procedures apply to both interior and exterior all-skies.

DUPLICATION

1)  During the duplication of correctly exposed all-skies, we've found that for most projection applications, a correction of 1 f/stop overexposure is necessary to make the image appear near what it does under ordinary projection conditions.  This is to compensate for the loss of intensity which a very large image is subject to.
2)  During duplication of under- and over-exposed originals, the contrast will increase in proportion to the number of stops the image is burned or dodged.
3)  When the subject matter is too high in the frame, it is possible to remount and adjust the all-sky by dropping the image as far down as is practical so that the duplicate will be better composed than the original.  All six images should have the same adjustment made to them.

MASKING

One of the most unattractive features of all-skies is "all-sky wash-out."  This effect is produced by the over-amplification of incident light bouncing around inside a dome, especially when there are large portions of sky in each of the images.  Because of diffusion, contrast  decreases so that what appears as a blue sky under ordinary projection will now appear nearly white.  This whiteness further obliterates any pertinent details.  To counteract this, masking out the sky (and whatever else may produce such wash-out) is a very effective way of re-investing your all-skies with greater impact. 

There are several ways of making kodalith masks.  One method uses a calibrated copy stand, a fiber-optic projection system such as Nikon's Slide Magic accessories with a Nikon camera, and a set of photo-floods. Whatever the method, the slide image has to be projected onto white card stock; the outline of each image has to be traced; the parts to be eliminated are left white on the paper and those that are to remain are painted black with tempura paint. When photographing the paper masks with kodalith, the exact calibration used during projection must be maintained.  When the masks are ready, tape them over the all-skies and opaque out any light leaks and other inconsistencies.  Your all-skies will suddenly take on new life, and you will have another creative masterpiece to draw upon. 

That ends this instalment of The All-Sky Circle.  Our next feature will be an exploration into Unconventional All-Skies, using photographs, artwork and combinations of single images to produce astounding effects with your system.  Until then, have fun and shine on!

NOTE: Since the publication of this article, much of the preparation for generating finished all-skies and panoramas has gone digital. Programs such as Photoshop, Bryce, Polydome and Digidome have revolutionized the way in which full dome imaging is created. A complete article on producing digital all-skies and panoramas will be included in these pages.