Ultra wide angle lens the difference is only whether distortion is present or not. However, the shorter the focal length, the more difficult it is to implement rectilinear correction. In fisheye lenses, the visual angle is close to or more than 180 degrees in at least one direction. For example, a "diagonal fish eye" would have a viewing angle of at least 180 degrees within the diagonals of the frame. A "circular fisheye" would represent the image in the form of a circle. Rectilinear ultra-wide angle lenses are used in photography and cinematography sometimes to achieve three-dimensional perspective distortion instead of simply two-dimensional barrel
Straight leg raise more specific, the ankle can be dorsiflexed and the cervical spine flexed. This increases the stretching of the nerve root and dura. If the patient experiences sciatic pain when the straight leg is at an angle of between 30 and 70 degrees, then the test is positive and a herniated disk is a possible cause of the pain. A negative test suggests a likely different cause for back pain. A meta-analysis reported the accuracy as: If raising the opposite leg causes pain (cross or contralateral straight leg raising): Lasègue's sign was named after Charles Lasègue (1816-1883). In 1864 Lasègue described