Photography, oriented

The unit of exposure is the stop, and one stop is a factor of two. Two stops is four times the light and three is eight, not six. A stop is the same amount of light whichever control supplies it, so you can hand one from the shutter to the aperture and keep the brightness. That is an equivalent exposure: the same brightness, a different photograph, because the depth, the blur or the noise has moved. Exposure value (EV) collapses aperture and shutter into one number, so every pair at the same EV admits the same light.

The meter is a measuring instrument, not a judge. It assumes an average scene and drives it toward a mid-gray of roughly 18 percent reflectance, so it has no way to know your scene is white. Say you photograph a sunlit snowfield and accept the meter's reading. The snow comes out dull gray, because the camera did exactly what it was built to do. Plus compensation fixes it, and minus compensation fixes the mirror case, a coal-black subject that came out too light. For a check without any meter, bright sun at f/16 wants a shutter near one over the ISO, about 1/100 at ISO 100.

The trap is protecting the wrong end. Clipped highlights hold no data at all, while dark shadows can usually be lifted, with noise as the cost.

Rule: decide what the subject cannot afford to lose, protect that control, and let the meter's number be a starting point you correct.

An f-number is a ratio: f/4 means the opening is a quarter of the focal length. Brightness falls with the square of that number, because light passes through an area. Multiplying the f-number by about 1.4, the square root of two, halves the light, so each full stop is that factor apart: f/4 admits half the light of f/2.8 and twice that of f/5.6. Count positions on that series rather than dividing numbers: f/2.8 to f/8 is three stops, eight times the light, not the "about three times" that 8 divided by 2.8 suggests. Most cameras click in thirds, so three clicks make a stop.

Depth of field is the zone that looks acceptably sharp, and sharpness fades gradually rather than stopping at an edge. Stopping down deepens the zone. Subject distance matters even more: halving it roughly quarters the zone, which is why close-ups have almost none at any aperture. Focusing at the hyperfocal distance keeps everything from about half that distance to infinity acceptably sharp.

The trap is assuming the smallest opening is the sharpest. Say you shoot a landscape at f/22 for maximum depth. More of the scene falls inside the zone, but diffraction, light spreading at the edges of a small opening, softens the whole frame. Most lenses peak two or three stops down from wide open, between wide-open aberrations and small-aperture diffraction.

Rule: choose the aperture for the depth the picture needs, count stops on the series, and stop down past the middle range only when the extra depth is worth an overall softening.

The shutter decides how much time the photograph holds. A longer exposure gathers more light and gives everything more time to move. Movement across the frame needs a much faster shutter than movement toward you, because sideways motion sweeps across the sensor while head-on motion mostly changes size. Blur can also be a choice: a slow shutter on a tripod turns a waterfall smooth, and panning with a moving subject keeps it sharp while the background streaks. To get a slow shutter in daylight, a neutral density filter cuts light in stops: a ten-stop filter turns 1/60 into about 17 seconds, ten doublings rather than ten times.

Before fixing a blurred frame, diagnose it. If everything is smeared, the camera moved; if one thing is smeared, the subject did. For handheld work, a rough limit is one over the focal length, so a 200mm lens wants about 1/200. On a cropped sensor, multiply the focal length by the crop factor first, so 35mm on a 1.5 times body wants about 1/50. Stabilization rated at four stops stretches 1/200 to roughly 1/13.

The trap is reaching for stabilization when the subject is the thing moving. Say a child is running across a dim room at 1/30. A stabilized lens steadies your hands and does nothing for the child, so the only cure is a faster shutter, paid for with aperture or ISO.

Rule: name the blur before you fix it; shake is solved by support or stabilization, subject motion only by a shorter exposure.

Raising ISO brightens the recorded signal and its noise together. Doubling it is one stop, so ISO 100 to 400 is two stops. The base setting is the cleanest and holds the widest range from highlight to shadow, because nothing is being amplified. Much of the noise comes from the light itself: photons arrive randomly, and that randomness dominates where they are scarce, in the shadows. That is why shadow noise appears even on an excellent sensor, and why collecting more light is the only real cure. Noise reduction cannot tell noise from fine texture, so every increment of smoothing removes some real detail with it.

Dynamic range is the span of stops one frame can hold, and it shrinks as gain rises. When a scene is wider than the file, something must clip, and the choice is yours. Blending a bracketed series works for a scene that holds still. A graduated filter darkens a bright sky in one exposure. Fill flash lifts the shadows instead of lowering the highlights.

The trap is setting ISO first. Say you are photographing a friend indoors and dial in a high value before thinking about anything else. The file is noisier than it needed to be, when a wider aperture or a slower shutter the scene could tolerate would have bought the same brightness with real light.

Rule: set the aperture and shutter for the picture, give ISO whatever brightness is still missing, and when a scene exceeds the range, pick which end must survive.

Focal length, in millimeters, sets magnification, and it does not change when you move the lens to another body. What changes is how much of the projected image the sensor records. Multiply by the crop factor to get the full-frame angle of view, so 50mm on a 1.5 times body frames like 75mm. A normal lens roughly matches the sensor diagonal, about 43mm on full frame, and gives a perspective close to unaided vision.

Perspective, the relative size of near and far things, is set purely by distance. A longer lens at the same spot only crops. The flattened look of a telephoto shot comes from standing far away, which the long lens lets you frame. The stretched look of a wide-angle close-up comes from being close, which a wide lens invites.

The trap is blaming the glass. Say a head-and-shoulders portrait taken with a wide lens at arm's length makes the nose look large. Zooming wider or narrower from that spot will not fix it; stepping back and framing with a longer lens will.

Lenses also carry flaws worth knowing by name. Color fringing comes from different wavelengths focusing at slightly different points. Optical corner darkening lessens as you stop down. A 1.4 times teleconverter costs one stop and a 2 times one costs two. A polarizer cuts reflections from nonmetal surfaces and deepens blue sky, at a cost of one to two stops.

Rule: choose where to stand for the perspective you want, then choose the focal length that frames it from there.

Single autofocus acquires once and locks, which lets you recompose. On a moving subject it focuses where the subject was. Continuous autofocus keeps adjusting while you half-press, so it follows someone running toward you, but it cannot hold a reading while you recompose. Phase detection compares two views of the scene to learn which direction to drive the lens, which is why it is fast; contrast detection hunts for peak contrast, slower but accurate.

Where you put focus matters as much as how. In a portrait, focus on the near eye; a sharp far eye reads as a mistake. In a landscape, focusing at infinity wastes the near half of the available depth. In street work, zone focusing presets an aperture and a distance range so you never focus at all.

Autofocus needs contrast and a guess about your subject. It struggles in the dark, on blank surfaces, through foliage or glass, and in close-up work. Those are the cases to take over. At night, one method is to switch to manual and focus on a distant bright light, such as a star or a streetlight. Focus peaking and a magnified preview let you confirm the result.

The trap is focus and recompose at a wide aperture. Say you lock on an eye at f/1.4 and swing the camera to place the face off center. The focus plane swings with it, and the eye can fall out of a zone only centimeters deep. Move the focus point instead.

Rule: pick the focus mode by whether the subject moves, and place focus where the picture needs it rather than where the camera lands.

A source that is small relative to the subject gives hard light with sharp shadow edges. A large one wraps around and softens them. The sun is vast but far away, so midday sun is hard, and the shadows it casts from a nose and brow rarely flatter a face. An overcast sky turns the whole sky into the source, which softens shadows almost to nothing. Direction matters too: front light flattens, side light reveals form and texture, back light separates the subject from its background. Early morning and late afternoon light arrives low, so it is warmer and models a scene with long shadows.

Color temperature runs against intuition: low Kelvin numbers are warm and high ones are cool, from about 1900 K for a candle to 5500 K for daylight and 8000 K for open shade. White balance is one correction for the whole frame, so two sources with different temperatures cannot both be neutral. A raw file stores white balance as an adjustable setting rather than baking it in.

Light from a nearby source obeys the inverse square law: doubling the distance quarters the illumination, which is two stops, not one. A close light therefore lights two people a step apart unevenly.

The trap is fixing mixed light later. Say a flash lights a face in a tungsten-lit room. Correcting for the room turns the flash-lit face blue, so match the flash to the room with a colored gel at the shoot.

Rule: decide what the light should reveal, then change the source's size, direction, distance or color, rather than hoping processing will.

Placing a subject on the third lines, or near one of their four crossings, leaves room for the rest of the frame to do something. That is why the guideline works more often than not. Centering reads as formal and direct, so it suits symmetry; commit to it or clearly leave it, because half-centered looks accidental. A line gives the eye a path, so ask where the path ends. A road leading out of the frame carries attention away from your subject. A doorway or overhanging branches can enclose a subject and add depth.

Attention goes to what is large, bright, contrasty, saturated, sharp or human. Notice where your own eye lands first; if it is not the subject, something else is winning. Horizon placement declares which half matters, high for the land and low for the sky. A slight tilt reads as a mistake, so straighten it. Camera height changes the relationship too: low makes a subject imposing, high makes it smaller.

The trap is a subject too small in a busy frame. Say you photograph a friend in front of a famous arch from across the parking lot. The picture is mostly pavement and other visitors, and a lamppost rises straight out of your friend's head. Walk closer until the subject fills the frame, then check every edge and the background before you press the shutter. Getting closer also changes perspective, which zooming does not.

Rule: name the subject in a few words, then move, reframe or wait until everything in the frame either supports it or is gone.

A raw file holds data captured by the sensor with very little processing, plus metadata such as the white balance setting. Turning it into a picture takes processing on a computer, so every rendering decision stays open. A JPEG, a format developed by the Joint Photographic Experts Group, is a finished picture whose contrast, color, sharpening and white balance were decided in the camera. Its lossy modes discard detail for good, and its data is limited to 8 bits per channel, which is 256 levels. That is plenty for viewing and thin for heavy editing: pull a smooth sky apart and the steps show as banding.

The histogram shows where the tones sit, not whether the picture is good. Read its ends, where clipping lives, and check the color channels separately, since one saturated channel can clip while the combined graph looks safe. Editing that stores instructions apart from the original lets you revisit any decision. For the web, sRGB is the safe color space. For print, multiply inches by pixels per inch: a 10-inch print at 300 pixels per inch needs 3000 pixels across.

The trap is one copy. Say your only archive is a laptop and the laptop is stolen. Keep at least two copies of the photos that matter, on separate media, stored as far apart as you can manage. Check them at least once a year, and copy them to new media every five years or so.

Rule: capture raw when you mean to edit, judge exposure by the histogram's ends, and treat a backup as real only after a second copy in another place.

A portrait usually pairs a wide aperture to separate the subject, a slightly long lens to avoid close-range distortion, and focus on the near eye. A landscape protects depth and range with a small aperture and base ISO. Those two force a slow shutter, so a tripod makes the rest possible. Sports protect the moment with a fast shutter, continuous autofocus and a burst, and ISO takes whatever is left.

Night skies show the logic clearly. Leave a shutter open too long and the stars streak into trails, because the Earth keeps rotating. So you protect the shutter's upper limit and spend everything else. Park rangers suggest a wide aperture, about f/1.4 to f/3.5, a shutter of 10 to 20 seconds, and a starting ISO near 400 that you raise as needed. A rough trailing limit is 500 divided by the focal length, about 25 seconds at 20mm. Use a tripod and a self-timer or remote, and focus manually on a distant bright light.

Architecture protects straight verticals: pointing the camera up makes parallel walls converge, so keep it level and step back or climb higher. Documentary work protects the record: tone, contrast and color adjustments are accepted, while adding, removing or moving content is not.

The trap is copying a genre's settings without knowing what they protect. Say you borrow landscape settings for a toddler's party. The tripod and slow shutter guard depth you do not need, and every running child blurs.

Rule: name the one thing this picture cannot lose, fix that control first, and let the others follow.