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.

Center-Weighted Metering Pattern

Center-weighted averaging is a bit more “old fashioned” in that it is how light was read, for the most part, before advanced microprocessors got into the mix. The light is read from all parts of the viewfinder, with 70% of the light reading coming from the center of the frame and the remaining 30% of the calculation from the edges of the frame. It is called “averaging” because it takes in all the various brightness levels and then averages them to what is called a “middle gray” exposure reading. This is the basis for much of how metering and translating light value works, so is worth some consideration.

When the metering system receives light from the scene it attempts to average the exposure values so that the bright areas record as bright and the shadows as dark, in essence arranging the light values along a scale of light and dark. Let's say you are working with a scene where there is a range of values, from the bright white in clouds to the deep shadow of a valley. If you read the clouds alone with a spot meter they might read f/11. The edge of the valley might read f/8; the shadow area reads f/5.6. An averaged exposure would be f/8. This “places” the brightest clouds as a highlight, the edge of the formation as the middle value and the deep shadow as quite dark. Thus, exposing at around f/8 places the brightness values as they appear in the scene.

Because the pupil of the camera (the lens opening) is fixed at the moment of exposure, there is no leeway for adjusting to various levels of brightness within the frame. This means that one exposure time has to handle all the lights and darks in a scene, and try to get detail from them all. This is, as you can imagine, a delicate situation. How it is handled is to arrive at an exposure that allows in just enough light to bring detail into the dark areas (the shadows) and not get overwhelmed by the bright areas (the highlights.) This is usually an average of the two intensities of light. The average reading sorts out the lights and darks accordingly so some records as brighter than the average and some darker than the average, as it should be.

Although the exposure system is quite sophisticated you too have to do your part. In essence, the information you “feed” the brain of the meter is the information it acts upon. In exposure that means making a reading by pointing the camera and sometimes locking exposure values to get it right.

For example, let’s say light values EV 11, EV 7 and EV 9 exist in the scene. A change in 1 EV (exposure value) is one stop difference. The average of these three readings is EV 9, which we’ll call f/11 at 1/125 second. That’s the reading the meter will recommend and set for you. EV 9 then becomes the middle gray of the light to dark brightness value, or tonal scale of that image. In essence, the meter has read and set up a range of tones that will be recorded. With EV 9 as the middle gray, EV 11 records as a brighter value and EV 7 as a darker value.

If, however, the reading was made incorrectly and the middle gray was set at EV 7 (which you would get if you just read the shadow areas) then the EV 11 (quite bright) value would record as very bright, and result in overexposure. Conversely, if the middle gray were EV 11 (created if you just read the highlight area) then the EV 7 reading would become much darker than it appears to your eye. All the values work in lock step, so making a bright value a middle gray makes all the dark values darker (and perhaps underexposed, where no detail is seen) and making a dark value middle gray can cause all the bright values to become quite overexposed.

A sunset scene is a classic shot for center-weighted metering. The intent is not to get detail in the ground but to use it as a form that offsets the sky and defines the horizon line. The simplest approach to sunset shots where you want to have a rich sky is to use center-weighted metering, aim the camera at the sky (not the sun!), lock exposure and shoot. Use this method and you’ll never miss a dazzling sunset again.

This might seem quite confusing in the abstract, but working with the camera and making readings exclusively from certain brightness values in the scene, and observing results, will quickly show you how this system works. In fact, you can even make use of this knowledge to create very expressive exposures.

The key to center-weighted reading is to "bias the exposure" towards the highlight. In other words, point the camera towards the highlight area (including other areas as well) and make the reading from that area. This is especially true if the highlight area sits at the corner or out of the center of your framing.

Photo and text copyright George Schaub 2010. In this scene the camera was set on center-weighted metering pattern, pointed towards the brighter area in the upper right, and then exposure was locked and the image reframed to the compositon you see here. Matrix or evaluative would have undoubtedly overexposed the highlights in this scene.

Basics: Lens Aperture

Exposure is controlled by the aperture and the shutter speed settings. The aperture setting also influences depth of field, thus plays a major part in creative focusing decisions. Aperture settings are called f-numbers, and are expressed by "f/" followed by the number of the aperture set.

Aperture settings are indicated on a lens by a series of numbers; with some cameras and lenses there is no aperture scale on the lens barrel and the settings appear in the camera's viewfinder and/or LCD panel. A typical aperture scale might read: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16. Each number indicates the ratio of the actual diaphragm opening to the focal length of the lens in use, thus any same aperture on any lens always allows in the same amount of light. As these are actually fractional numbers the smaller numbers signify larger openings. Thus, f/2 (or 1/2) represents a wider opening (or greater value) than f/16 (or 1/16).

As mentioned, f-numbers represent the same light value regardless of the lens or format in use. Thus, f/2 on a 50mm lens for a 35mm camera delivers the same amount of light through the lens as f/2 on a 200mm lens for a medium-format camera, even though the diameter of the openings themselves are different. If this wasn't the case the entire light control system in photography simply wouldn't work.

Each subsequent number in an aperture scale represents a halving or doubling of the amount of light that the aperture allows through the lens. (You can calculate the next higher number in any one-stop-step scale by multiplying the previous number by 1.4). Each step in the scale (say, from f/2 to f/2.8) is called a stop. Thus, every time you open up or close down the lens by one stop (opening means going to the next lower number, or wider opening; closing down means going to the next higher number, or narrower opening) you are changing the amount of light entering by the power of 2. A one stop change (say, f/8 to f/5.6) is a 2X difference; a two-stop change (sat f/8 to f/4) is a 4X difference; and so forth.

The best way to see how aperture settings effect light transmission is to take the lens off the camera, hold it up to the light and click through the aperture settings. (Note: Some lenses do not allow for aperture changes on the lens itself, but rely on the camera to change apertures,) You'll see that the maximum aperture, say f/2, is the widest opening. As you click through the scale, you'll see the diaphragm in the lens getting smaller. Think of water as it flows through a pipe. Given that the water will always fill the pipe, a larger diameter pipe will allow more water through. This can be applied to light flow and the aperture diameter.

Most lenses and cameras today allow for partial stops, like older lenses with click stops, or detents, between the aperture settings. On older lenses these are half-stops, and though not marked indicate a halfway point between the two aperture numbers on the ring. On newer lenses you can have 1/3, 1/4 or other fractional spreads. These step-less aperture settings means any value can be set, such as f/9.7 or f/11.3. These values are indicated in the camera viewfinder and/or the LCD panel on the camera.

Aperture rings are usually inscribed with all the available full stop settings on the lens, from the maximum, or widest, to minimum, or narrowest lens opening. The range of the aperture scale may differ depending upon the construction of the lens and its focal length. One scale may read f/2, 2.8, 4, 5.6, 8, 11, 16, while another may read f/4, 5.6,8, 11, 16, 22, 32 (the latter is more typical of zoom or telephoto lenses.) The lowest number in the scale (thus the widest opening) is called the maximum aperture; the highest number on the scale (thus the narrowest opening) is called the minimum aperture.

Photo and text copyright George Schaub 2010. Aperture settings allow you to control the depth of field, what appears sharp and unsharp in your photo. To get focus from foreground to background here an f/16 setting was used.