An Occassional Glossary: C, D, E

Here's a bit more on the ongoing glossary project, C through E

Center-weighted Metering Pattern: In a metering scheme, an exposure system that takes most of its information from the center portion of the frame. Most center-weighted systems also take additional readings from the surrounding areas, but weight the reading towards the center.

Color Balance (digital camera): The setting in a digital camera that matches the available or artificial light to faithfully renders color.

Color Temperature: Described by the Kelvin scale, which is defined in degrees. It is used as a standard for judging the effect or color cast a certain light source will have on color rendition.


Continuous: The shooting mode that allows for continuous firing without lifting the finger from the shutter release button In tonality, a smooth range of tones from black to white. In autofocus, allowing shutter release regardless of whether subject focus has been attained.

Contrast: The relationship between the lightest and darkest areas in a scene and/or photograph. A small difference means low contrast; a great difference, high contrast. High contrast scenes may cause exposure metering problems; however, their “difficulty” can mean they hold the potential for more expression. In addition, combining bracketed exposures, HDR and tone curve compensation techniques can overcome high contrast challenges, Though contrast is often linked with scene brightness, there can be low contrast in a bright scene and high contrast in dim light. Contrast can also describe attributes of color, composition, and inherent qualities of film and sensors.

Correct Exposure: The combination of aperture and shutter speed that yields a full-toned image and the best possible representation of the scene. The constants in an exposure calculation are the ISO or sensitivity of the sensor and the brightness of the scene; the variables are the aperture and shutter speed.


Dedicated Flash: A flash that coordinates with the camera's exposure, and sometimes focusing, systems. Dedicated flashes may, among other things, automatically pick up the camera’s ISO setting, set the camera sync speed, and "tell" the camera when it’s ready to fire. Flashes dedicated to autofocusing cameras may also vary their angle of flash throw (coverage) according to the lens in use (even with zoom lenses), and emit autofocus beams that aid focusing in very dim light or even total darkness. For outdoor work, dedicated flashes may provide totally automatic fill flash exposure. In short, a dedicated flash can make flash photography as simple as automated natural light photography.

Depth of Field: The zone, or range of distances, within a scene that will record as sharp. Depth of field is influenced by the focal length of the lens in use, the f-stop setting on the lens, and the distance from the camera to the subject. It can be shallow or deep, and can be totally controlled by the photographer. It is one of the most creative and profound image effects available to photographers.

Depth-of-field Preview Button: A switch, button, or electronic push button on SLRs that allows the photographer to preview the depth of field of a selected aperture in the viewfinder. During composition the lens is wide open, thus the depth of field in the viewfinder is always that of the maximum aperture of the lens. DOF Preview is very useful for critical selective focus shots.

Dynamic Range: The ability of a sensor to record a certain range of light.

Electronic Flash: Known as a flashgun, strobe, or speedlight, a device consisting of a gas-filled tube that is fired by an electrical charge. It can be mounted directly on the camera hot shoe (which links the shutter release to the flash firing), or on a bracket or stand, and be connected to the camera via a sync cord or wirelessly through IR beams or radio signals.

Equivalent Exposure: Recording the same amount of light, even though aperture and shutter speeds have shifted. For example, an exposure of f/11 at 1/125 second is equivalent to an exposure of f/8 at 1/250 second.

Exposure: The amount of light that enters the lens and strikes the sensor. Exposures are broken down into aperture, which is the diameter of the opening of the lens, and shutter speed, which is the amount of time the light strikes the film. Thus, exposure is a combination of the intensity and duration of light.

Exposure Compensation Control: A camera function that allows for overriding the automatic exposure reading. The bias, or shift, can be set in full or partial stops. Used in difficult lighting conditions, when the reflective meter might fail (that is, dark or bright value dominance), or for deliberate under- or overexposure of a scene. Can also be used to bracket exposures.

Exposure Meter: Light-reading instrument that yields signals that are translated to f-stops and shutter speeds.

EV Numbers: A system of expressing exposure that combines apertures and shutter speed. Scene brightness translated to aperture and shutter speed values. For example, EV 15 at ISO 100 might mean 1/1000 second at f/5.6, or 1/500 second at f/8. EV numbers are often used as shorthand for the combined aperture and shutter speed value combinations and are used for making exposure compensation, when doing autoexposure bracketing or for readouts of exposure.

Very Selective Focus

There are a number of lenses that allow you to break the rules of depth of field. Because you can shift and tilt these lenses on an unusual axis not parallel to the image sensor, you can correspondingly tilt (up and down) and shift (side to side) the planes of focus in the photo. This technique is often used by large format, view camera photographers to attain unusually deep depth of field, where the shifts and tilts can be coordinated between both the front (lens stage) and back of the camera itself. Because the back of a DSLR is rigid there is less freedom of movement, and while specialty lenses can be used to create very deep depth of field, I use them for creating an almost angular plane of focus, thus a very shallow depth of field and “odd” focusing effects. What is most unusual is that these lenses allow you to turn the rules of depth of field on their head, if you will, by allowing you to have sharpness in, for example, one subject six feet away on the right side of the frame while another subject six feet away on the left side is quite unsharp.

While you can attain this effect via software, shooting with lenses that mount on your camera in the field is a much more visceral and engaging activity. I have used two types of lenses for this work-- “Lensbabys”, with various options for effects and operation, and a PC (perspective control) lens. Both are available for most every make of DSLR. They require manual focusing but usually can be used with automatic exposure, albeit with some occasional exposure compensation required.

PC lenses have a tilt and shift mechanism with various knobs and locks on the barrel. This allows you to tilt the lens to and fro and shift plus and minus. If you look at the back of the lens you will notice the rear element is recessed into the barrel. This so-called retrofocus-type construction allows the lens to be swung to and fro because the coverage of the lens circle exceeds the diameter of the sensor or film. Most of these pricey lenses are constructed so the tilts and shifts do not cause excessive vignetting, although you should watch for that with some more extreme movements.

You can play with the planes of focus in odd ways with one of the Lensbabys (www.lensbaby.com). This replaces the normal lens directly on your camera and allows you to shift the focusing planes so they are not parallel to the camera, something that is at odds with how we think about photographic sharpness. You do this by literally twisting or pressing down on one side of the lens; the bellows in the mount give way to make the lens surfaces sit at odd angles to the sensor. The lens can be shot wide open (usually about f/2.8) as supplied, or you can insert small diaphragms that create various aperture settings. I usually don’t use those stops as I want as shallow a plane of focus as possible.

Tools: PC (perspective control) lens or one of the Lensbaby models. Live View if available. Aperture priority or manual exposure mode. Manual focusing.

Depth of Field

The aperture setting determines the “thickness of the pipe” through which light flows, thus the volume of light and exposure. But as, if not more importantly it influences depth of field, thus plays a major part in creative focusing decisions.

You can think of depth of field as a grid of distance markers from the front to the back of your photo, sort of like a football field. When you make different aperture settings you are influencing how sharp objects at the ten, twenty, thirty yard lines, etc, will be. You are also influencing how sharp they will be in relation to the point or distance you actually have focus set.

Some settings will make the difference of sharpness between, say, the ten and thirty yard lines quite dramatic, and others will make it less so, and others will eliminate any sharpness difference between those distant points.

How can we control the fact that this image shows sharp foreground trees as well as the massive falls miles away? That’s the kind of control depth of field gives you. With a 24mm lens, exposure at ISO 250 was f/9 at 1/125 second.

Obsolete So Soon? A Look Back at Early Digicams

The rush of events in the past few years has left us all fairly breathless, what with the pace of change wrought by digital. As product trumps product, and new operating systems and formats rush to grab our attention, older systems and gear quickly fall by the wayside. Some have come to rest in my Museum of Photographic Obsolescence (MOPO). The halls of that hallowed institution have become quite crowded of late; a new wing is being built as you read this.

You needn’t go too far back to find tech and gear that vie for space in that exhibition hall. Look through the back booths of a book store and you might find a few ragged copies of 1940-1950 era Pop Photo or even good old Modern Photography and been amused by the proliferation of ads for movie projectors, tape recorders and even some old Federal enlargers, once staples on a dealers’ shelves. But I didn’t have to reach that far back to find some goodies and more recent exhibits for the MOPO; indeed, many came to the fore when I did some spring cleaning recently and discovered some clippings from writings past. I thought you might get a kick out of some of the hyperbole and prognostications.

Here’s one, from July of 1984. The lead reads: “Eastman Kodak Company announced its entry into the consumer electronics field at CES last January when it introduced the Kodavision Series 2000 video system.” According to then VP Roger Sharp, ‘Most reactions from dealers indicate they are particularly happy to see ½ inch video cassettes on their shelves... It will provide another incentive by making it easier for people to take electronic home movies and play them back through their VCRs.” Along with a classic hardware entry into the Halls of the MOPO, I counted one major technology and one format that went down the tubes from that release. (Anyone recall Polavision? Yes, that’s in the days when marketers didn’t capitalize mid-word.)

In the same year, there was some prognostication that was not too far off the mark. Buried about five paragraphs down from a frothy lead about the future of video still cameras, Mikio Ashikawa of Toshiba was quoted as reporting that to overcome the resolution hurdle, video still cameras might catch up to film by “not increasing the pixels but in electronic rearrangement of the available information, that is, image enhancement through computers.” The movement of that enhancement from desktop to inside the camera is what marks digital imaging today.

The article goes on to say, “Many scientists (at the SPSE conference in 1984) feel that electronics and film will make a happy marriage, with film serving as the input and electronics taking care of the processing side of the business. One scenario is that film, once developed, would be scanned by a device that converts the information into digital form and then that data would be put through various image producing and enhancing channels.” Well, that wasn’t too bad, even in 1984.

It’s always fun to read ad and promotional copy from years past, only because some of it seems almost naïve in light of what we’re experiencing today. I quote from Nikon copy from 1999 not to pick on Nikon, but to illustrate how quickly things have changed. Indeed, everyone was caught up in the same game.

After a flurry of promotional matters the copy goes on to say: “Now, Nikon asserts that (digital photography) leadership again with the announcement of two new digital cameras—the Coolpix 950 and 700—both of which break the 2 megapixel barrier in the affordable, under $1000 digital camera category. This means that photographers can now record uncompressed TIFF images as large as 6MB, resulting in never-before seen quality in affordable cameras.” The changes this press material mark from just eleven years back are glaring. The 2MP cameras are now gone, or relegated to toys; that model category, though non-existent today, would be probably $1300 in 2009 dollars; the camera, if sold now, would probably be 10% of the then asked for price of “under $1000”; and of course TIFF as an in-camera format has for the most part gone away. The memory cards of the time were also quite expensive, and those prices have dropped 80-90% from 1999 as well.

And while we’re on cameras, just for fun I pulled a 1987 PMA report that breathlessly reported “tremendous gains in the electronic still photography field in the past year.” Known then as ESP (electronic still photography) there was the Panasonic Photovision 3100, which recorded 300K images on a 47mm video floppy disk; the Konica SV-C40 (another 300K unit which could fire off four frames per second in the “higher resolution” frame mode); and the Fujix ES-2P, which delivers “380K images, resulting in higher picture quality than most similar cameras.” These video still cameras have a special hall in the evolutionary exhibits in our MOPO.

One of the most interesting pieces from the yellowing archives was an interview done with Robert C. Davis, then president of Bremson Data Systems, in 1985. In response to what we might see in 1995 (ten years from the date of that interview), Davis said: “The big question on everyone’s mind is whether silver halide based imaging is going away. Everyone’s concerned with that…You may get a system where you dump in a roll of film at one end and out the other will come pictures and negatives all wrapped together, and in between you may get a videotape and a video disk along with it. At that point a (pro) photographer may be showing his proofs on a video screen...The professional may begin to use electronic cameras in the studio. We may get a cartridge, or a floppy disk, and put it in a processor and out will come 11x14s to wallet packages. Package work may bypass film. It all depends on how fast the U.S. and Japan will develop the chips necessary to do that—there’s still the resolution problem to deal with.” Most prescient for 1985 eh?

The mid-eighties saw digital photography as just a glimmer in some engineers’ eyes. In each sector—camera makers and photo processors—the groundwork was being laid for the coming sea changes in photography. The point of me bringing all this up is that we might just be in a similar period today. The changes wrought over event he past three years are incredible. We even have people today who are quite avid photographers who never exposed a picture on a roll of film in their life. Where this might lead, and what formats, gear and technology that are now the hot items will be new entrants in our MOPO, is anyone’s guess. But we can all rest assured that what we see as breakthroughs today will be quickly overtaken by what’s just around the corner. And we might look back in 2030 with similar amusement about how naïve it all seems in 2010. Or will we gain that perspective by 2011?

Creative Focus: Part 1

At first glance it would seem that focusing is a simple matter. You look through the lens, press the shutter release button to activate the autofocus mechanism and make the photograph. Or, when using a manual focus lens, merely turn the focusing collar on the lens until the image seems sharp in the viewfinder, and then press the shutter release. This would work fine if we lived in a two-dimensional world. Yet subjects in most scenes sit different distances from one another. Some may be close together while others could be miles apart. Working with focusing techniques you can either make subjects at great distances appear sharp within the picture or have a background that is as close as a foot to your subject appear unsharp.

Focusing is one of the most important creative options. The technique for creative focusing play is called selective focus or depth of field, and it is based on the idea of “circles of confusion”, or what our eyes perceive as sharp and unsharp in an image.

Think of a magnifying lens slanted toward the sun and a piece of paper receiving the rays of light through the lens. As you move the lens back and forth the rays from the sun form a circle or a point on the paper. When a lens is mounted on a camera it directs light toward the film or sensor. Those rays that converge on the film or sensor at a point, or at a near point, are what we perceive as sharp in the image. Those that form a circle beyond a certain diameter are perceived as unsharp in the image.

Our eyes tolerate a certain diameter of circle, or “blob” as being sharp. We do this at a certain distance and with a certain degree of magnification of the image. Change the viewing distance and/or the magnification and what appeared as sharp might later seem unsharp. That’s why when we enlarge prints that looked good in a snapshot size print (4 x 6 inches) to 11 x 14 inches the print may look slightly unsharp. Close inspection of image before enlargement can help prevent this problem.

Next: Viewfinders and Live View

Photo and Text copyright George Schaub 2010. Depth of field controls set up what is sharp and unsharp in the photograph. A deep depth of field, as shown here, means the eye perceives everything from front to back as in focus, or sharp.

An Occassional Glossary: A, B

AMBIENT LIGHT: The light in the scene, as opposed to the light provided by the photographer with flash, photofloods, etc.

ANGLE OF VIEW: The maximum angle a lens covers in the field. Measured in degrees, and qualified by terms such as wide-angle, normal, and telephoto. A wide angle lens has a wider angle of view than a telephoto lens.

APERTURE: The opening of a lens, the size of which is controlled by a diaphragm. The term aperture is also used to designate f-stops, such as f/4, f/5.6 etc. Actual aperture size may be different on different lenses but always allow in the same amount of light. Thus, f/11 on a 110mm focal length lens allows in the same amount of light as f/11 on a 28mm lens. The wider the opening, the lower the f-number, the more light is let through the lens.

APERTURE PRIORITY: An autoexposure mode in which you select the aperture and the exposure system selects the appropriate shutter speed for a correct exposure. Sometimes referred to as Av or simply A on exposure mode control panels.

ARTIFICIAL LIGHT: Any light not directly produced by the sun. Can be tungsten, flash, household bulbs, sodium vapor street lamps, etc.

AUTOEXPOSURE: A method of exposure where aperture and shutter speed settings are first read, then set, by the camera itself. Various autoexposure modes allow you to customize, or bias the automation.

AUTOEXPOSURE LOCK: A pushbutton, switch, or lever that locks in exposure after you have made a reading, regardless of a change in camera position or light conditions. Useful for making highlight or shadow readings of select portions of the frame, and an essential feature for critical exposure control with automated cameras.

AUTOFOCUS: A method of focusing where focusing distances are set automatically. In SLRs, a passive phase detection system that compares contrast and edge of subjects within the confines of the autofocus brackets in the viewfinder and automatically sets focusing distance on the lens. Autofocusing motors may be in the camera body or the lens itself. Active IR (infrared) autofocusing systems may also be in some cameras in the form of beams that are emitted from the camera or flash, bounce off the subject, then return and set focusing range, and are used when light or contrast is too low for the passive system to work.

AUXILIARY LENS: An add-on optical device that alters the focal length of the prime lens for closeup, telephoto, or other special effects photography. Closeup lenses, for example, usually comes in +1, +2, and +3 powers; the higher the number the greater the magnification. As differentiated from Lensbaby optics, auxiliary lenses are usually added onto the camera lens via the threads on the lens collar.

AUXILIARY LIGHT: A flash, strobe, or tungsten lamp or bulbs used to change the character of light in a scene. Any light under the control of the photographer.

AVAILABLE LIGHT: The light that's normal in a scene, although the term is generally used when the light level is low. Available light shooting usually involves high ISO settings, low shutter speeds and apertures, and/or the use of a tripod.

AVERAGING: In light metering, a metering setup where the light is read from most of the viewfinder frame (70%) then averaged to yield an overall, standard exposure for the scene that averages all the values read to middle gray.

B or BULB: A shutter setting that indicates that the shutter will remain open for as long as the shutter release is pressed. The term originated with the rubber air shutter bulbs used to operate shutters in the old days. B settings are generally used in nighttime and time/motion study photography.

BACKGROUND: The portion of a scene that sits behind the main, foreground subject. We can make the background sharp or de-focused through the use of selective focus techniques.

BACKLIGHTING: From camera position, light that comes from behind the subject. Usually, a backlit main subject will be underexposed unless the metering system is set to read selectively off the subject. Extreme backlighting can be exploited to create silhouettes.

BATTERY: The power supply of the camera and flash. In many of today's cameras (and certainly in flashes), no power means no pictures.

BLACK-AND-WHITE: Monochrome images. Though we think of black and white mainly in terms of a grayscale, monochrome images can have a wide variety of subtle tones, from blue- to brown-black.

BLUR: Unsharpness because of the movement of the camera or subject during exposure. Though we usually want images sharp, blur can be used for many creative effects.

BOUNCE LIGHT: In flash photography, directing the burst of light from the flash so it literally bounces off a ceiling, wall, or other surface to illuminate the subject. This method of flash is often preferred because it softens the overall light and eliminates the harsh, frontal look of an on-camera, straightforward flash.

BRACKET: Making exposures above and below the normal exposure, or that which is suggested by the camera's autoexposure system. Useful as a failsafe method for getting "correct" exposure in difficult lighting conditions. Bracketing can also be used to make subtle changes in the nuance of tone and light in any scene and is an essential ingredient in HDR processing.

BRIGHTNESS: The luminance of objects. The brightness of any area of the subject is dependent on how much light falls on it and how reflective it is. Brightness range is the relationship we perceive between the light and dark subjects in a scene. Brightness contrast is a judgement of the relative measure of that range, such as high, low, or normal.

BURNING-IN: In processing, giving additional density (dark tones) to a portion of a print or image.

BURNT-OUT: Jargon that refers to loss of details in the highlight portion of a scene due to overexposure. It might mean that no image detail has been recorded, or that highlights show no texture or tonal information.

Photo and text: copyright George Schaub 2010. Backlighting is when the main light in the scene sits behind the subject facing camera position. It can be used for creating silhouettes or here as a combination of silhouette and translucent light quality.

Spot Metering

One of the three options you have for a metering pattern, or the area in the viewfinder where the metering system takes its information to calculate an exposure, is known as “spot.” The spot options generally takes its information right from the center of the viewfinder and is often defined by a small, etched circular pattern. Some Custom Functions allow you to define the exact circumference of the spot area or move the spot to match a focusing point.

Because spot metering is quite exclusive it does require that you occasionally use it in conjunction with exposure compensation. Like all metering it converts what it reads to a middle gray, so if you meter a white area and want it to record as white you have to add exposure to the reading; conversely if you meter a very dark area and want it to stay dark as seen then you have to take away exposure.

The best way to add or subtract exposure when using a spot meter is to use the exposure compensation feature. You can preset this at +1.5 when, for example, shooting on a bright snowy day and reading from the brightest areas. This should insure that you get texture in the bright white (although it still might shadows areas to become underexposed.)

Spot metering also aids in making readings from smaller areas within the scene, such as a backlit face. In that case no compensation is required.

The easy rules for spot are:

When you spot bright white add exposure (usually +1 or +1.5EV) if you want to render it bright white in the recording.

When you spot a color you will saturate that color.

Text and photo Copyright George Schaub 2010

To saturate the bright yellow and red here all it takes is placing the spot pattern on the color and locking exposure.