For a 35mm single lens reflex (SLR) camera, a standard or normal lens is generally from about 40mm to 58mm. However, the most common size is 50mm. This of course, will be different for other film formats. This focal length gives a field of view about the same as what the eye gives. You basically get about the same image you would if you looked at the subject with one eye. Some people prefer the wider angle of view of a 35mm lens for a 35mm camera. Others feel that 85mm focal length lenses are better suited for general use as they easily fill up the picture frame with subject matter. A standard lens enables you to photograph people if you do not get too close to them. If you fill the frame with the person's face you will usually get a distorted image. If you stand back at a little further and get their shoulders in the photo it should be distortion free. 50mm lenses range in price from about $50 to several thousand. Lenses come in different apertures and in auto and manual focus models.