The embodiment of the invention discloses a prime lens. The prime lens includes a first lens with negative light focal power, a second lens with negative light focal power, a third lens with positivelight focal power, a diaphragm, a fourth lens with negative light focal power, a fifth lens with positive light focal power, a sixth lens with positive light focal power, a seventh lens with negativelight focal power, and an eighth lens with positive light focal power, which are arranged successively along an optical axis from an object side to an image side, wherein the fourth lens and the fifthlens form an adhesive lens; the first lens, the fourth lens, the fifth lens, and the sixth lens are spherical lens; and the second lens, the third lens, the seventh lens, and the eighth lens are non-spherical lens. The technical scheme of the embodiment of the invention can be applicable to the field of security and defense. The lens has the characteristics of day and night confocal function, excessive large amount of light and an ultra-wide angle, especially suitable for use under a low illumination condition.