CN2690908Y - Imaging device for fingerprint identifying device - Google Patents

Abstract

The utility model relates to an imaging device for fingerprint identifying device, which is characterized in that a double telecentric imaging objective is composed of three separated lens arrays; the lens array in the middle is negative and the lens arrays on both sides are positive; each lens array is composed of one or a plurality of pieces of lenses. By obtaining good correction of all image errors including a curvature of field, the double telecentric imaging objective of this form can make the imaging quality of scene with all fields of view reach or approach the limit of diffraction, besides, the conjugate distance is short.

Description

The imaging device of finger-print recognising instrument

Technical field

The utility model belongs to fingerprint identifying optical system.

Background technology

The imaging device of finger-print recognising instrument is the front end fingerprint signal input instrument of fingerprint recognition system, its optical system is made up of total reflection prism and image-forming objective lens basically, group object lens and back group object lens before the image-forming objective lens group is divided into again, the inclined-plane of total reflection prism is the fingerprint input window, when finger when printing on the prism inclined-plane, according to the principle of optical total-reflection, on image planes, can be observed and only observe the fingerprint image of high contrast.Fingerprint image can produce the change of two kinds of form shapes in transmittance process, and the one, the inconsistent distortion of magnification of meridian and arc square direction, if promptly thing is a square, then image is a rectangle, can be described as rectangular distortion.Prism wedge 3 among Fig. 1 is used for proofreading and correct this distortion.Another kind of deformation is trapezoidal distortion, and promptly thing is a square, and image is trapezoidal.A kind of method of proofreading and correct trapezoidal distortion is designed to two hearts far away with image-forming objective lens, the emergent pupil that is the summit of the preceding one side of going into the interpupillary distance object lens of object lens and object lens is infinity or near infinity apart from the summit of back one side, also promptly goes into interpupillary distance and the emergent pupil focal length apart from one group of lens of focal length and back of last group of lens in object lens.Preceding positive lens groups 4 among Fig. 1 and rear lens group 7 and light hurdle 6 are two telecentric imaging object lens that two positive lens groups of separating are formed.Chief ray 9 among the figure is all parallel with optical axis 5 with picture side at object space, i.e. interpupillary distance is gone in expression and the emergent pupil distance is infinity.From in form, the characteristics of two telecentric imaging object lens are that the bore of front lens group is very big, be slightly larger than the size of object plane, and the object lens of back are much smaller.Two telecentric imaging object lens of using in the existing fingerprint instrument imaging device are all this by two groups of forms that positive lens groups is formed of separating.Its shortcoming is for making the outer visual field of axle, and especially the image quality of visual field, edge meets the demands, and must strengthen conjugate distance (object plane is to the distance of image planes), so can increase the volume and weight of instrument.So being not suitable for being used in four, two telecentric imaging object lens of this form refer in the such imaging device of fingerprint instruments and palmmprint instrument the exigent big visual field of image quality, multiplying power (ratio of image height and object height).

Summary of the invention

The utility model is intended to overcome above-mentioned shortcoming.The finger-print recognising instrument imaging device mainly comprises area source, fingerprint input window, prism, Guang Lan, imaging lens, CCD image planes, and the not high reason of picture element of an outer visual field of two telecentric imaging object lens of being made up of two positive lens groups of separating mainly is that this aberration of the curvature of field can't be proofreaied and correct.In order to proofread and correct the curvature of field, also be simultaneously in order to shorten the distance that rumbles altogether, the technical program is characterised in that two telecentric imaging object lens are made up of three lens combination of separating, and the centre is a negative lens group, and both sides are all positive lens groups.Each group lens all can be made up of a slice or several lens.Owing to comprise that all aberrations of the curvature of field can better be proofreaied and correct, therefore two telecentric imaging object lens of this pattern may accomplish to make image quality in the full visual field to reach or near diffraction limit, and conjugate distance is lacked.

Description of drawings

Fig. 1 is the two telecentric imaging object lens figure that are made up of two positive lens groups, among the figure: 1, light source; 2, total reflection prism; 3, prism wedge; 4, preceding positive lens groups; 5, optical axis; 6, Guang Lan; 7, rear lens group; 8, CCD image planes; 9, light main shaft.

Fig. 2 is the utility model image-forming objective lens figure, and among the figure, 10 is negative lens group.

Embodiment

Accompanying drawing 2 has provided the utility model image-forming objective lens, forms one by preceding positive lens groups 4, middle negative lens group 10, back positive lens groups 7 and light hurdle 6 and is used for four finger fingerprint instrument catadioptric imaging object lens.Do not proofread and correct rectangle deformation because this structure requires, therefore need not add prism wedge.The object plane of present embodiment is of a size of 80 millimeters * 75 millimeters, the imaging multiplying power is-0.289, and as number formulary value aperture NA=0.12, conjugate distance is 253.5 millimeters, use wavelength to be λ=0.66 μ m (per mille millimeter), also available white light (λ=0.4-0.7 μ m) imaging.In full field range, frequency is 120 pairs of lines per millimeters, transport function greater than the 0.5. maximum distortion less than 1%.

Claims (1)

1, finger-print recognising instrument imaging device, comprise light source, fingerprint input window, prism, Guang Lan, imaging lens, CCD picture pick-up device, it is characterized in that two telecentric imaging object lens are made up of three lens combination of separating, the centre is a negative lens group, both sides are all positive lens groups, and each group lens all can be made up of a slice or several lens.

Images