Basic information 1 An introduction to basic camera controls

Transcription

1 Basic information 1 An introduction to basic camera controls

2 Camera types Compact Camera Small, lightweight but limited advanced controls Small sensor size Bridge Camera Advanced features comparable to SLR but non interchangeable lens Small sensor Digital SLR Interchangeable lenses, larger sensor, More usable for advanced photography Large sensor size

3 Sensor size The larger the sensor size the higher the resolution of the images you will get. Because of the way sensors are created, the small sensors produce more electronic noise that a large one. Think of a small transistor radio. To reach a distant station you have to turn up the volume and get a hissing, crackly background noise. That is the same with image sensors. A larger Hi-Fi will have a more sensitive tuner and give a much cleaner signal Canon's 1Ds/5D and Nikon D3 series are the most common full frame sensors. Canon cameras such as the 60D/7D all have a 1.6X crop factor, whereas mainstream Nikon SLR cameras have a 1.5X crop factor. Compact cameras and Camera phones use sensor sizes in the range of ~1/3" to 2/3"

4 Lenses Lenses are constructed of several elements, chosen to reduce problems. E.g. basic lenses will focus different colours at different points, resulting in out of focus areas. Other elements introduce distortion Zoom lenses are the most difficult to produce as they need to keep focus at all focal lengths. The smaller the lens, the more difficult it is to remove distortions

5 The Aperture The aperture is a reduction of the apparent diameter of the lens to allow less light to pass through. The size of the hole is mathematically calculated so that each is a ratio of the lens diameter. E.g. Πr 2 and is denoted as f: e.g. f16 The common ratios are 1.2, 1.4, 2, 2.8, 4, 5.6, 8,11,16, 22. Many lenses also have ½ stops for finer control. The larger the number, the smaller the aperture. The step from one f-number to the next is known as one stop and it represents halving (or doubling) the brightness of the image. Shutter speeds are denoted in the same way, with each speed is a doubling or halving of the shutter opening time. The shorthand is that 125 actually means 1/125 second If at the same time as closing down the lens one stop or stopping down ( say from f4 to f2.8) and doubling the shutter speed (say 125 to 250 ) the net exposure will be the same

6 Focusing Standard lens focussed on the Middle boy 2m/ 6ft away. At f2 gave a depth of field of m /6-7ft The same lens at f16 shows all three boys in focus. The depth of field extends from m /4-15ft

7 Depth of Field Depth of Field (DoF) is the zone in front and behind the point at which you have focussed. Depth of field is an optical illusion. It depends on the focal length of the lens, the aperture used, the size of the final image and the distance it is viewed from. There is a point on every lens that is known as the Hyperfocal distance. If the lens is set to this point the depth of field extends from half way from you to the hyperfocal point and infinity. This is how cheap fixed focus cameras can take sharp pictures. How can we use that fact? To get the largest DoF focus approximately one third into your picture.

8 DoF & Sensor size One of the downsides of compact cameras is that the small sensors make the necessary lenses minute and very short focal lengths. The optimum focal length for a standard lens (one that gives the closest apparent view as your eye), is equal to the film diagonal dimension. For full frame 35mm the image is approx. 24 x 36mm and so the lens is 50mm Focussed at 10ft at f16 this will have a DoF of 17ft extending from 6.3 to 24 For the small sensors the lens range is about mm (35mm film equivalent: mm) Taking a nominal 8mm at f16 focussed at 10ft will have a DoF of 2.5 to infinity

9 DoF & Sensor size -2 Dropping to f2.8 we still have a DoF of 6.5 to 21.5 On most zoom lenses the maximum aperture varies from f 2.8 to f5.6 Both of these factors make it more difficult to obtain good selective focus. (the means to throw a background out of focus on portraits, etc.) The longer the focal length of a lens the shorter the depth of field e.g. a 200mm lens on a 35mm camera has a DoF of 9.8 to 10.2 at This fact can be used to good effect on a compact. At 21mm and DoF is 8.6 to So counter intuitively; to take a good portrait on a compact camera you should use the longest zoom So how do you get maximum DoF for a landscape?

10 Optical vs Digital Zoom Another aspect of compact cameras is that there are often two types of zoom mechanism Although a camera may be described as having an 8x zoom only the first half (4x) is produced by the optical lens The remaining part is performed digitally. This means that the camera takes smaller chunks of the optical image and blows them up to give the apparent zoom. This reduces the quality of the image, sometimes considerably. It amplifies any digital noise and leads to further degradation.

11 Shutter speeds Shutter speeds are like a time machine. The shutter speed determines how much or how little time it is open to record the subject motion. Using a very fast shutter speed you can freeze motion or a long exposure can extend the image so that blur can reveal more about the subject. The normal range is normally from about 1/125 sec to 1/1000 sec in order to stop motion from subject movement or your own shaking. The correct method of holding a camera can improve the sharpness of your images You should squeeze the shutter button; as stabbing at it will cause the camera to move. There are more blurry images on the Internet for this cause that sharp pictures. Speeds lower than 1/125 need firm support for the camera with a tripod or other means. Demonstration of how you should hold your camera

12 Sensitivity In the days of film there were several methods of calibrating the sensitivity to light of film BS, DIN, ASA & ISO were the popular ones but ISO has become the standard for digital The higher the number the greater the sensitivity but there are pitfalls. The steps between ratings show a doubling in sensitivity 100, 200, 400, etc. The high ISO ratings are accompanied by noise, again akin to the transistor radio. Noise is also controlled by sensor size, so the larger the sensor the less noise. Many Compact cameras try to mask the noise by other means and hide it in a mushy image. Most of the DSLR manufacturers have made great strides in sensor design to reduce noise

13 Controlling the image Sometimes the correct exposure is not always the right way to convey a mood Too dark? Too blurry?