Underwater Photography Glossary
1:1 magnification A lens can achieve 1:1 magnification if it can take a photo the size of its sensor. On a Nikon D300, this would be 24 millimeters across. Not all lenses that claim to be "macro" lenses can achieve 1:1 magnification
35mm equivalent A len's focal length multiplied by the sensor's crop factor. A 60mm lens on a D300, which has a 1.5 crop factor, in 90mm in 35mm equivalent.
ACR Adobe camera raw
Ambient light Light from the sun, also called natural light
Angle of view A measure of how wide a view a lens has.
Aperture Circular opening behind your lens that lets light in. The diameter changes as you change your f-stop.
Barrel distortion A type of distortion, common in less expensive wide-angle lenses, where straight lines at the edges of the image start to appear slightly curved. This can be corrected in software. Fisheye lenses exhibit a great amount of barrel distortion, but this is the intended effect.
Base ISO The ISO of a camera that gives the least noise and greatest dynamic range. ISO 100 on most cameras, ISO 80 on some point and shoots, ISO 200 on some dSLRs.
Beam angle A measurement of how wide of a beam a strobe will put out. Beam angles of 90-110 degrees are common for strobes suitable for wide-angle photography.
Bit depth number of bits of data the camera stores per pixel; 12 or 14 bits
Bokeh The Japanese word for "blur". A measure of how pleasing the background of an image is blurred. Different lenses blue the background differently, resulting in different "bokeh".
Bracketing Shooting a subject 3 times, shooting the 2nd and 3rd shot at higher and lower exposures, to try to ensure a correct exposure.
http://www.uwphotographyguide.com/sites/all/modules/fckeditor/fckeditor/...); background-repeat: no-repeat; background-position: 0px 50%; ">Chromatic aberration A type of distortion that manifests itself as "fringing" of colors along high-contrast boundaries. Because substances have slightly have slightly different refractive indexes, for different wavelengths of light, colors end up being focused on different points on the images.
Color temperature A number, in degrees Kelvin that tries to represent the approximate color of the light. Higher numbers are cooler, more blue. Lower numbers are warmer, more yellow or red.
Contrast the difference between the lightest and darkest part of the photo...
Crop factor The crop factor is the sensor length / 35mm. 1.3 – 1.6 is the range for most cropped-sensor dSLRs, 1.0 for full frame dSLRs, 2.0 for Olympus dSLRs.
Cropped sensor A camera with a crop factor greater than one.
DOF Depth of field. It's the area of an image that appears sharp or in focus.
Desiccant A chemical that absorbs moisture.
Diffraction A loss of sharpness at 100% magnification as a resulting of shooting at too small of an aperture
Diffusion The softening of light because the light is coming from multiple sources. Can be caused by various substances such as tissue paper, clouds, a translucent window, a milk carton, haze, or a diffuser on a strobe. A byproduct of diffusion is softer shadow boundaries.
DSLR Digital single lens reflex
Fast lens Lens with an aperture of F2.8 or larger; usually auto-focus fast, even in low light
Flashgun Another term for a strobe
Focal Plane A plane parallel to your camera sensor that is in perfect focus
Front curtain sync A camera mode where the flash fires as soon as the shutter opens. This is the default mode in all cameras.
Full frame A camera with a 35mm width sensor.
Guide number A number that represents how strong a strobe is. It's f-stop number X distance to subject (in feet or meters). Guide numbers can be in air or underwater. The numbers underwater will be much smaller.
Hot Shoe the slot on top of a camera that accepts an external flash, or a hot shoe cord from a housing.
Hyperfocal distance the minimum distance you can focus at while still having infinity distance in focus. Follow this link for more info: http://www.dofmaster.com/hyperfocal.html
IQ Image quality - a somewhat vague term used by the masses about the image quality a lens will produce in the right hands
Lembeh stick - metal rod worn around the wrist, to push yourself away from the reef or sand without using your hands or feet. Used by many dive guides in Lembeh straits.
ISO Stands for International Standards Organization. A measure of how much a signal from your camera sensor is amplified
JPEG Stands for Joint photographic experts group. A lossy, compressed file format, the most common format for images.
Lens element - a single piece of optical glass inside a lens; modern lenses often have several lens elements inside
Lens speed Maximum aperture of a lens
Matrix metering A method of calculating exposure that only uses a large area. Also called evaluative metering.
Minimum focus distance distance from the camera sensor to the subject at the minimum focusing distance; slightly different that working distance, but often interchanged
OEM Original equipment manufacturer
Prime lens A lens that has a largest aperture of at least F2.8m or larger
Pixel Smallest unit of color & brightness in an image. Originally comes from "picture element"
Rear curtain sync A camera mode where the strobe fires right before the shutter closes. This mode can be specially set on most dSLR’s. When used with slow shutter speed, this mode will give the effect of a motion trail behind the subject.
Refraction Refraction is the bending of light as it passes from one medium to another. The light changes speed and direction. The wavelength of the light will change, but not its frequency. Refraction occurs when light passes between water and air, and it responsible for causing objects to appear larger than they are, and also forSnell’s window. Here is a visual demonstration: http://www.ps.missouri.edu/rickspage/refract/refraction.html
Reproduction ratio The ratio of image size to sensor size. 1:1 means a lens can take a photo of a subject the same size as its sensor. 1:3 means the smallest object a lens can photograph is 3 times the size of the camera sensor. Reproduction ratio = 1 / maximum_magnification. See the lens tables for lists of maximum magnifications for various lenses.
Sensor The silicon chip inside your camera that converts photos of light coming from your lens into voltages.
Shutter sync speed Same as strobe sync speed
Slave strobe - a strobe that fires when it sees another strobe fire
Spot metering A method of calculating exposure that only uses one small area.
Stop down Reducing your aperture, e.g. – going from F8 to F10
Strobe falloff - the rule the says the light from a strobe decreases in power proportional to the square of the distance from the strobe. the strobe power = C/(X*X), where C is a constant, and X is the distance between the strobe and the subject. moving a subject from 1ft to 2ft away from a strobe will reduce its power by 1/4th.
Strobe sync speed The fastest speed at which a normal strobe can be used with a camera. Normally it is 1/200 to 1/320th on dSLRs with mechanical shutters. Electronic shutters will allow faster sync speeds, but this may result in reduced strobe power if the speed is faster than the strobe sync speed.
Strobe sync speed (second meaning) The speed at which the light of a strobe flashes, often around 1/10,000th of a second.
Slow lens Lens with a largest aperture greater than F2.8. A slow lens will have trouble auto-focusing in dim light
Sync cord An electronic cable that connects your strobe to a camera or TTL converter
Sync speed - the fastest shutter speed at which you can use strobes with your camera
Stopped down Shot at a smaller aperture. A F5.6 lens shot at F8 is said to be "stopped down" 1 f-stop.
TTL "Through the lens" - a mechanism to automatically evaluate and set exposure my measuring the light coming through the lens;
http://www.uwphotographyguide.com/sites/all/modules/fckeditor/fckeditor/...); background-repeat: no-repeat; background-position: 0px 50%; ">Vignetting Light falloff in the corners of an image, usually when too small of a port or a filter blocks light from reaching the corners. If the lens is a zoom lens, zooming in often eliminates the vignetting.
Working distance - the distance from the lens front element to the subject, at the minimum focusing distance
Zoom lens - a lens with a variable focal length
All text copyright 2009 by Scott Gietler, all rights reserved