digitaldingus Reference

Digital Photography Definitions

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September 30, 2015

Terms & Definitions

digitaldingus has updated the Digital Photography Definitions area to flow more intuitively, as well as be readily available for those looking for particular terms and definitions on either a desktop computer, or their portable media device such as a tablet and smartphone.

Term Definition
µm µ (Micron) + m (Meter) = Micrometer. You will see this symbol when looking at the specifications of pixel sizes (e.g., 7.8µm, 7.4µm, etc.). A micron is one millionth of a meter. Or looking at it this way, it's 1/1,000,000 of a meter. It's also 39.37 micro-inches, but I wouldn't suggest using inches since the International Standards Unit (ISU) does not recognize the United States' measurement system. A micrometer is what the "µm" symbol represents.
AA Filter See Low Pass Filter.
Initially announced January 5, 2016, this type of lens includes stepping motors to initiate the AF motor. Currently, AF-P lenses are only available on DX format lenses.
This is a step-up from your ordinary AF lens. Ultrasonic motors are used in these kinds of lenses, making the movements of the lens element groups, virtually silent. Ultrasonic waves are used to move the lens elements back and forth. AF-S lenses are also famous for lightning-fast focusing. Again, this is because of the ultrasonic technology, which is used by other manufacturers under different names.
Amp Glow This refers to an imager which has "glowing" areas, usually from any of the 4 corners of the chip. Long exposures cause this, and digital cameras use DFS (Dark Frame Subtraction) to remove most of this glow. In most cases, the light will be saturated the most at the corners of the imager, and will gradually taper off at an equal radius towards the center of the imager.
Angle Of View AOV; Field Of View; FOV. A portion of the subject/scene, which is covered by a lens. The amount of the subject or scene covered by a lens, depends on the focal length of the lens. A 300mm lens will have a very narrow angle of view, while an 18mm lens will have a wide angle of view. The specific "angle" of this view, are almost always included in the specifications of the lens. For example, a Nikon AF-S ED 80-200mm f/2.8D IF lens has a 30°10' - 12°20' AOV.
Aperture As far as photography is concerned, it is the size of the opening in a camera lens, expressed in numbers with an "f/" before those numbers, that allows light in. The larger the numbers, the smaller the size of the opening in the lens, the smaller the numbers, the larger the size of the opening of the lens.
APO (Sigma) Apochromatic. Sigma uses APO to designate their lenses which have SLD or ELD glass. The APO designation is used for their telephoto lenses and lenses which have a rather extended focusing range. The question might be asked why APO lenses are only concerned with longer focal lengths. The answer is due to the way red wavelength behaves. Ideally, you want Red, Green, and Blue wavelengths of light to focus at exactly the same area on your lens. This would (ideally) result in the best image representation. At shorter focal lengths, this does occur (mostly), but at longer focal lengths, the red wavelength of light tends to shift more than the other two wavelengths.

What this means is if you're shooting your subject which contains a red wavelength, it will probably appear out of focus when compared to the other two wavelengths on your image (and vice versa). For those seeking more explanation, I suggest investing some time into reading about Infrared Photography, which requires the photographer to take into account this particular shifting of wavelength. APO lenses are designed to compensate for the red wavelength shift at telephoto focal distances.

If you want to extend the focal length of your telephoto lens with a TC (teleconverter), be sure you have a TC which is APO compliant (i.e., has APO glass in it as well), as you will NEGATE the effects of that expensive APO glass in your lens. This is why some TCs are cheap...and some are not.
APS-C APS-C refers to the size of a sensor that has a diagonal measurement of about 29mm. The Sigma DC lenses, such as the 50-200mm and 18-50mm are meant for APS-C sensors. What this means is any sensor which has a larger diameter of 29mm (or 28.75mm to be exact), will not work. APS-C sensors, like their film counterpart, are 23.4mm x 16.7mm. Most DSLRs currently available (Nikon D-series, Canon D60, 10D, 300D, Fuji S2, and many others), are APS-C, however, the Canon 1D, 1D MK II, and the full-frame DSLR Canon 1Ds, are not APS-C. 1D sensors are slightly larger, and Sigma DC lenses will not work properly (i.e., severe vignetting will occur) on these cameras.
Art (Sigma) First announced in 2012, Sigma began to create a much higher standard lens series, along with a much needed tighter quality control. For those seeking top-quality lenses who don't necessarily want to stick within their typical Nikon and Canon loyalties, Sigma's Art lenses should seriously be considered.
Aspect Ratio The ratio of width to height of an image. For example, you may see imagers having an Aspect Ratio of 3:2, or like the Olympus E-1 sensor, which has a 4:3 ratio. Some prefer one ratio over another due to printing sizes, but since most photographers crop images to fit their own particular style, this ratio is virtually worthless, and if anything, should only give you an indication of the ratio of the sensor itself. Most imagers on cameras have a 3:2 ratio, and to find a different ratio would be no further than the Four-Thirds System, created by Olympus many years ago.
Back Focus If the camera appears focused when zoomed in, but becomes out of focus when zoomed out (i.e., at its widest focal length), the back focus needs adjusting.
Back-Illuminated CCD BCCD. In order to get a high Quantum Efficiency rating of around 90% or higher, the CCD imager is "thinned" to a thickness of around 10-20 microns. Then, the CCD is placed face-down, where the light is now absorbed throughout the back of the CCD. Anti-reflection coatings can also be used on the BCCD (unlike a Front-Illuminated CCD which is why the QE is so low), thereby reducing refraction of Photons. What this means is, BCCDs have significantly less photons bouncing (i.e., reflecting) off its imager because of high absorption at all wavelengths of light.
Blooming This has to do with a digital imager (sensor), and its pixels which become highly overexposed. Because the pixels can only contain so much light, the light then spills into surrounding pixels. It's easy to do this with digital cameras versus film. The EV feature on your camera, if improperly set, will give you a bloomed image. Blooming is also related to pixel size.
BMP Bitmap; .bmp. The standard bitmap image format on Windows-compatible computers, but not all browsers support BMP. BMP files should be avoided for storing images entirely. True, they can contain 24-bit data, however, using a more widely used storage format such as JPEG, or if you shot in RAW, your own camera manufacturer's RAW format, is recommended.
Bokeh The quality of the rendering of the shapes of the aperture blades of a given lens, within an image. With a high-quality lens, you have many aperture blades, which creates a more "circle-like" appearance to OOF (Out Of Focus) objects and subjects. This is somewhat subjective, because you may have more or less tolerance for a specific rendering of the bokeh of an image. Generally speaking, good bokeh means your OOF subjects have circluar shapes, and bad bokeh is when you actually see the "stop-sign" effect, which is, you see the jagged edges of the aperture blades in the rendered image.
Camera Shake A condition where a lens at a low-shutter speed (generally around 1/60sec or less) and small vibrations to the camera or surrounding lens, caused by external or internal sources, produce blurred photos.
CCD Charge Coupled Device. A type of imager which is used in digital cameras, CCTV cameras, and many other devices. CCD chips are relatively cheap, compared to other imager types. Note that CCD imagers require more power to operate than its competitor CMOS chip, which does affect ISO levels and image quality. However, camera companies can offset some of this problem with superior software processing. Pixels on CCD imagers also have a distinction from CMOS sensors, by not having "on-pixel" processing.

This definition is being written at the end of 2015, and CCD imagers are not used too often when it comes to DSLRs or cameras in general. CMOS has taken over and is a proven superior imager type.
Chromatic Aberration CA as it is often referred to when discussing it, is related to a pixel being overloaded, overexposed, or overcharged with light. One of the tests which test CA problems on a digital camera, is to take a photo on a relatively clear day, and point the lens up into a tree, covering several branches and leaves. What you will see, is a "purplish" outline around the edges of the leaves. If your camera is subject to Blooming, CA will be much more prevalent in your images.
CMOS Complementary Metal Oxide Semiconductor. Pertaining to imaging, it was one of the various kinds of imagers we saw around the first of the 21st Century. CMOS was favored initially by Canon over any other kind of chip because it required less power to operate. The more power it takes to power an imager, the more susceptible it is to noise. Other kinds of imagers are CCD, Nikon's LBCAST, and Foveon's X3 imager. Currently, CMOS is taking the lead in imaging technology as higher resolutions are attained. With Canon's announcement of a 250 Megapixel CMOS imager, it is clear the camera industry is taking the path of CMOS.
CompactFlash CF. CF was the primary form of media used in digital cameras and many other digital devices. First introduced by SanDisk in 1994, CompactFlash cards come in two different types: Type I and Type II. All CompactFlash cards are Solid State, which mean there are no moving parts to overheat. Current capacities of CF cards are now going into double-digit gigabytes. Due to cameras being more compact over the years, CF has pretty much taken second place to SD and MicroSD media formats.
D (Nikon) The "D" on Nikkor lenses, is in reference to distance. An internal encoder is connected to the lens focusing ring, and transmits the shooting distance information to the camera automatically. 10-segment Matrix Metering is an example of what a "D" lens can do when attached to your D-series DSLR. A Lens without a "D" means you will not be able to meter with your D-series DSLR. An example of a "D" lens is the 50mm f/1.4D.
Dark Current See Thermal Noise.
DC-Nikkor (Nikon) A special Nikon lens, which controls background and foreground blur precisely, enabling the photographer to produce very customized portraits or other kinds of images. Nikkor DC lenses are the only kinds of lenses with this feature in the world.
DC (Sigma) Not to be confused with Nikon's DC terminology, Sigma's "DC" lenses are much like Nikon's DX and Olympus' 4/3 lenses, in that, they are made for a specific size sensor--APS-C sensor. Sigma mentions these lenses are only made for APS-C sensors, which cover the size of most digital SLRs (Canon 300D, 10D, Fuji S2, all Nikon DX D-series DSLRs), except for the Canon 1D, 1D MK II, and 1Ds, and others, which are not APS-C sensor sizes.
Dead Pixel A dead pixel is a pixel which is black, and is not charged when light hits it. For example, you take a photo of a white piece of paper, and notice a few black pixels on it. These are dead pixels, meaning, they are dead. Don't work. No light is being accumulated in them. And so forth. Dead pixels will not display color.
Deconvolution This is a term describing the process of removing unwanted light artifacts from an image. For example, I capture a photo of a tree. Unfortunately, my lens absorbed reflecting light rays which have taken out some of the outlining areas of the tree. By using highly sophisticated "deconvoluting software", I can retain some of the original image. This term is mostly concerned with Astronomy or microscopic objects, where small details are considerably important. However deconvolution can also apply to ordinary photography as well.
DFS Dark-Frame Subtraction. A proven method in digital cameras where an image is taken at a low exposure, the digital camera then automatically takes a "Dark Frame" image soon after, then overlays the two images and processes them to the final output image. By doing this, Hot Pixels are removed from the image you shot, without taking away any detailed pixels from your image. Hot pixels are consistent, in that they stay in the same location over any low exposure, so the camera uses this data to remove them by comparing the image you took, and the Dark Frame image the camera took. Generally speaking, a Dark Frame image only contains hot pixels. Also, you don't have to rely on your digital camera to do the processing for you if it's not what you like. You can take your own DFS image and in a photo editor like Photoshop, compare the hot pixels and remove them; or simply remove the hot pixels in Photoshop by cloning or some other method.
Dicing This is the process of slicing a silicon wafer into parts, which then become Die.
Die After a silicon wafer is sliced by a special saw, these "slices" are now called die.
DG (Sigma) This refers to Sigma's wide-angle lenses having this designation, which are designed for digital SLRs (DSLRs). Sigma says these lenses provide a more even distribution of light from center to edge.
DL (Sigma) DeLuxe. This refers to Sigma lenses having this designation, which are supplied with a number of features and accessories, such as: a custom lens hood, DOF scale, distance scale, infrared correction mark, etc. Sigma says, "One or more of these features are usually missing from comparable lenses of similar price from other manufacturers, so the lens is considered DeLuxe".
DNG (Adobe) Adobe announced a new RAW format for photographers to use at Photokina 2004. Adobe is hoping that camera manufacturers will offer DNG in their future cameras. The idea, is that one day, you won't have to use multiple RAW software programs in order to read the metadata info and image data info correctly. Currently, Adobe is offering this converter for free.
DOF Depth Of Field. This is probably one of the most important aspects of photography. DOF is the degree to which the image appears to be in focus and sharp, or can mean the degree to which the image appears to NOT be in focus or sharp.
DPI Dots Per Inch. A measure of the resolution of a printer, scanner, or monitor. DPI refers to the number of dots in a one-inch line. The more dots per inch, the higher the Resolution.
DX (Nikon) This refers to Nikon lenses which have an image circle matched to the Nikon DX sensor. They will not work properly (i.e., vignetting will occur) if used on a Nikon 35mm camera.


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