Displaying images on the forums
Though most people viewing these forums have decent sized screens, some still view on lower resolutions and on mobile devices. To ensure images are easily viewable and loading times are kept down, images must be resized to be no larger than 800x600 unless they are panoramics.
Hotlinking of images (though this doesn't really apply in this forum) is banned on OcUK, so make sure you use your own webspace or one of the free image uploaders listed above to host your images. You can upload images to these sites straight from your computer and will be given a url link to the picture. Either click the 'insert image' picture and paste the url or wrap vBulletin tags around the image:
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EXIF viewers that display the information stored in a photo are available for both Firefox (
EXIF Viewer) and Internet Explorer (
Opanda IExif). To retain EXIF data in a photo when saving in Photoshop, use the 'Save as' command rather than 'Save for web'. JPEG quality 10 displays fine online and keeps loading times down.
Jargon buster
SLR and dSLR
SLR stands for 'Single Lens Reflex' and SLR cameras use a series of mirrors to allow the user to see the view through the lens through the viewfinder. When talking a shot, the shutter will move for the correct period of time to correctly expose the film or sensor of a (digital)
dSLR. Many modern dSLRs have a 'live view' function that either constantly exposes either the main sensor or a secondary one to display an image on the rear screen. Most dSLR cameras have a sensor smaller than a piece of 35mm film – crop sensors – and different manufacturers use different sized sensors. The most common crop factors are 1.5, 1.6 and 1.7 and to calculate the effective focal range of a lens, it's length should be multiplied by this number (a 50mm lens on a 1.6 crop Canon camera would have an effective focal length of 80mm).
Prime lens
A
prime lens has a fixed focal length (e.g. 50mm). Prime lenses are often smaller and lighter than equivalent zooms and have better optical properties (less chromatic aberration), being specifically designed for a specific focal length. Focus speeds are generally high and primes often have lower maximum apertures than zoom lenses, making them ideal for low light photography.
Zoom lens
These have a number of movable lens elements that can alter the focal length of the lens whilst retaining focus on a set point. Due to the complexity of the assembly and the number of lens elements involved, zooms typically have lower maximum apertures than primes.
Zoom lenses are named according to their length (e.g. 70-300mm), which also gives their zoom ratio (100-400 equates to 4:1 or a 4x zoom). Superzooms are zoom lenses that have a high zoom ratio, some being up to 10 or 14x. The concept of 'zoom' associated with point and shoot (P&S) cameras does not apply to SLR cameras, for example a 100-400 having a large end focal length (and effective magnification of the subject), but remains only a 4x zoom.
Telephoto lens
The term
telephoto is often exchanged, incorrectly, with zoom (although a zoom lens may be a telephoto, it need not be). By default, the focal length of a lens equals the distance between the front element of the lens and the sensor or film. With long lenses, the sheer length and weight of lenses would be a huge problem (telephoto primes are large and heavy enough as it is) and telephoto lenses incorporate a special lens group known as a telephoto group to allow the front element to be closer to the camera than would otherwise be possible.
Macro lens
The point of a
macro lens is to achieve a life-size (or as close as possible, or larger) image of an object on the sensor. True macro lenses, therefore, have a ratio of 1:1 (life-size) or higher (e.g. 5:1). Many zooms now have a 'macro' function, which do not allow true macro ratios to be achieved, but can attain around 1:4. Larger ratios can be achieved with extension tubes places between the camera and the lens, close-up lenses placed in front of the normal lens, reversed lenses and with a combination of a reversed lens and a normally placed lens.
Wide angle lens
Wide angle lenses have a focal length shorter than the diagonal length of the sensor or film. Full-frame and film cameras, therefore, have wide angle lenses with focal lengths below 35mm. When the crop factor of a common dSLR is taken into account, in order for a similar effect to be achieved, a lens must have an even lower focal length – many popular lenses being 10-20mm. At low focal lengths, significant barrel distortion is seen in the image, giving a fish eye effect.
Acronyms
Canon ...
DO: Diffractive Optics.
EF: Electro-Focus. Focus motor built into the lens - common to all EOS-mount lenses.
EF-S: Electro-Focus Short Back Focus. Lenses made specifically for crop-sensor EOS digital cameras. These lenses will not work on full frame bodies.
EOS: Electro-Optical System. Auto-focussing (d)SLR cameras.
IS: Image Stabilisation.
L: Luxury. Professional quality lenses.
USM: Ultrasonic Motor. Fast and quiet in-lens focusing motor
Nikon ...
AF-I: Autofocus Internal Motor. The AF motor is in the lens, rather than in the camera body.
AF-S: Autofocus Silent Wave Motor.
DC: Defocus Control. Allows control the spherical aberration of the lens.
ED: Extra-low Dispersion. Lens elements made to help correct chromatic aberration
G: D-type lenses. These lenses have camera controlled aperture settings only.
IF: Internal Focus. The front element of the lens does not move during focussing - the physical length of the lens remains constant.
Micro: Macro.
Sigma ...
DC: Lenses made specifically for crop-sensor digital cameras.
EF: Dual Focus.
DG: Lenses for on both crop and full-frame cameras.
DL: Deluxe. Indicates Sigma low-end lenses.
EX: Excellence. Indicates Sigma high-end lenses.
HSM: HyperSonic Motor. Fast and quiet in-lens focusing motor.
HZ: Hyperzoom. Lenses with extended zoom and focusing range.
ASP: Aspherical. Compact lenses with a reduced number of internal elements.
APO: Apochromatic. Lens elements made from special low-dispersion (SLD) to minimise colour aberration.
OS: Optical stabilisation. In-lens image stabilisation
RF: Rear focussing. The rear lens group is moved to achieve focussing.
IF: Inner focus. Inner lens groups are moved to achieve focussing - the physical length of the lens doesn't change.
Pentax ...
AL: Aspherical Lens.
ED: Extra low Dispersion. Lens elements produced to help correct chromatic aberration.
J: Lenses without external aperture ring - camera controlled aperture.
Sony ...
AIS: Active Interface Shoe. An electro-mechanical hot shoe on the lens for accessories such as microphones and lights. All power for the accessory is taken through this interface.
Tamron ...
Di: Lenses with optics designed to combat the increased reflectivity of digital sensors.
Tokina ...
ATX: Advanced Technology-Extra.
SZX: Manual focus lenses.
Aperture, shutter speed and ISO
Although there is no substitute for experimentation and trial and error, understanding the basics of aperture, shutter speed and ISO sensitivity is a good starting point. These three factors control the
exposure of a photo. For greater depth, Bryan Peterson's 'Understanding Exposure' is a good buy and various guides can be found by Googling – some of these are in the 'courses and tutorials' part of the 'useful links' section, above and are well worth a read.
The
aperture is the opening in the lens that allows light into the camera, its size being controlled by the diaphragm. The aperture of the lens is expressed as an 'f number', the ratio of focal length to aperture diameter. Understanding that this is a ratio helps to explain the apparent paradox that the largest apertures have the lowest f numbers (e.g. f/2.8 is a wide aperture, allowing a lot of light in) and the smallest apertures have the highest numbers (e.g. f/32, allowing very little light in). Lenses have pre-set 'f stop' values that can be selected often in thirds of a stop. Although it is not that important to know, a single whole stop increase (e.g. from f/2.8 to f/4) corresponds to a factor of √2 decrease in the size of the aperture. More importantly, this will halve the amount of light entering the lens. A single f stop decrease (e.g. from f/5.6 to f/4) corresponds to a factor of √2 increase in the size of the aperture and will double the amount of light entering the lens.
Apart from controlling the amount of light entering the camera, the other main effect of aperture is in controlling the
depth of field. This is the distance in front and behind a subject that appears to be in focus and is controlled by the distance of the subject, the focal length of the lens and the aperture (f number) being used. Larger apertures (e.g. f/2.8) give a shallower depth of field, smaller apertures (e.g. f/18) giving a larger depth of field and making more of the image appear to be in focus. A useful DoF calculator can be found
here.
Shutter speed is the duration of time for which the camera exposes the sensor or film. In lower levels of light, the shutter has to remain open longer than in higher levels of light for the same amount of light to enter the camera and for a set level of exposure to be achieved. Shutter speed is important, therefore, as longer shutter speeds mean that camera-shake and vibrations within the camera and lens can blur a photo. Controlled blur can often be the intent of a photo, however, for example when panning with a car to achieve a sense of movement. As a rough guideline to ensure a reasonable hit rate of acceptably sharp photos is to use a shutter speed of 1/focal length. This means that for a 50mm lens, a shutter speed of 1/50 seconds could be used and for a 300mm lens, 1/300s. With practice, sharp photos can be achieved with shutter speeds lower than this but with some longer lenses, you will never get a fast enough shutter speed using this calculation to allow you to easily hand-hold the camera and lens whilst shooting. To reliably achieve sharp longer exposures, monopods and especially tripods help massively. To a more limited extent, image stabilisation (either built into the camera or lens) also allows use of slower shutter speeds. Shutter speeds can also be increased by use of wider apertures (allowing more light into the camera) and by use of a higher sensitivity (see below).
ISO (or sometimes ASA with film) is the sensitivity of the film or the sensor to light. Higher sensitivities mean that less light is required to reach a set exposure level and faster shutter speeds can be used. As above, this has the effect of reducing the impact of camera shake and allows sharper images to be achieved. Within the exposure times capable of most cameras, there is a relationship that doubling the sensitivity (e.g. ISO 400 to 800) of the film or sensor and halving the exposure time (through doubling the shutter speed) will give the same exposure. A side effect of increasing sensitivity is an increase in
image noise, that can be seen as an increase in the 'graininess' of an image. Many digital cameras have settings to reduce image noise when taking long exposures and grain can be reduced relatively effectively in post-processing. Nevertheless, there is no substitute for using as lower ISO as possible in order to avoid image noise in the first place.
