Take into account the focal length extension factor when buying a lens(Digital camera)

             You were extremely happy when you got a good bargain on eBay. But you are now disappointed after some of the pictures with your new 18 mm lens. Instead of the expected eff ect of an extreme wide angle, the lens barrel is making subjects appear very plain and undistorted. What is wrong?
             Most of the image sensors in digital cameras are considerably smaller than the 35 mm format in analog cameras, which are rectangular and 24 x 36 mm in size. It is established as a fixed standard for comparison, with which the impression of different focal lengths can be described. Digital SLRs mostly use a so-called APS-C sensor (Advanced Photo System Classic) with page lengths of approximately 16 x 24 mm. As a result of this smaller sensor, the same lens, unlike a 35 mm sensor, maps only a smaller section of the subject projected through it. This is called focal length extension. This image circle factor is 1.5 in most SLRs, 1.6 in Canon and 2.0 in Olympus. When a 50 mm lens is used, the photogenic focal length is thus actually 75 mm in most cases and in case of Olympus, 100 mm. The focal length extension is a blessing for Tele-fans, but the situation is diff erent when it comes to the wide angle area. From your 18 mm extreme wide angle, an Olympus DSLR gives a standard focal length of 36 mm with a correspondingly good image mapping. For the desired wide angle effect, you need a DSLR lens with extremely short focal lengths. Their technical composition is, however, quite complex and are accordingly expensive.