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Focal Length with supplementary lenses can be lengthened or shortened. You can use ordinary glass spectacles. They are marked diopter numbers. All positive (collective) lenses shorten the focal length, whereas negative (scattering) lenses extend the focal lengths of lenses. Positive eyeglasses (collecting lens) can also serve as an independent photographic lenses. They give the desired in many cases, the softness of the art drawing, which, however, with a corresponding aperturing again disappears. If we combine these two lenses with the same or different focal lengths in one system, one can determine its focal length by dividing the total diopter numbers The distance to the object image, and hence the required stretching the camera will only equal to the focal length, the distance to the object is very large, so installation is done to infinity. The closer to the object of getting on the machine, the greater the need to stretch, until (at the pictures in full size), it does not rise to the value of double the focal length. Both quantities - distance to the object and stretching the camera - are always in a certain respect, which is dependent on lens focal length and zoom.

Sun cap

Purpose: Protect the lens from extraneous light rays, as well as rain and snow. Solar hood facilitates shooting against the light.