The depth of focus is a function of the used numerical aperture. Although it is theoretically same for telecentric and standard lens, in practice the useable depth of focus of a telecentric lens seems to be greater for a vision system or the human eye. The reason is the constant magnification in every focus position. Out of focus the image is just getting "softer", but positions of details and edges are correctly shown.
A line of telecentric lens systems is developed. Every system is a combination of front and back lenses. They are afocal lens systems with the aperture stops located at the common focus of the front and back lenses, resulting in the chief rays being parallel to the optical axis in both object and image spaces, i.e. both the entrance and exit pupils are at infinity. A constant perspective or viewing angle and a constant magnification can therefore be achieved in the cases when the object and image surfaces are tilted with respect to the optical axis or the lens is defocused on either object or image surface. Another feature is the large depth of focus, up to several milimeters, which is extremely useful in inspection applications. C-/T-mount adapters (GCO-230101~231206) are offered for coupling the lens to CCD cameras.

Specifications:

F-number:	Maximum 8.0 for all base lenses and any combination with base lenses.
Distortion:	<1% for 1/2" and 1/3" CCD; <0.5% for others
Telecentricity:	<0.3º defined as the angle of the chief rays with respect to th optical axis.

Specifications for Base Lens
Table 1

Catalog No.	D	I	Re	L	f	Object/image size	CCD size
GCO-2301	75	108	150	116.66	109.46	dia 50 or 40x30	-
GCO-2302	47.5	40.5	75	59.31	54.37	dia 25 or 20x15	-
GCO-2303	31	26.5	48	38.30	35.10	dia 16 or 13x9.6	1" (T)
GCO-2304	22	19.6	33	27.03	24.03	dia 11 or 8x6.6	2/3" (C)
GCO-2305	18	14.8	25	20.32	17.64	dia 8 or 6.4x4.8	1/2" (C)
GCO-2306	15	12	18	15.70	13.18	dia 6 or 4.8x3.6	1/3" (C)
GCO-2312	120	193	500	204.14	216.26	dia 100	-

- Relief: the free distance from the object or image plane to the first optical surface.
- Base lenses cannot be used individually, whereas any two base lenses can be incorporated into a telecentric system via an interface.

Combination of two base lenses into a telecentric lens system

Any two of the base lenses can be combined via an interface (GCO-230101-230606) to build a telecentric lens system, offering a specific magnification. Every base lens can act as either the front lens or the back lens, providing the object size or the image size as specified in table 1.

Catalog No.	Interface No.	Total Length	Conjugated Distance approx.	Object Size	Magnification Object/Image	Distortion @ image side	Weight (g)
GCO-2312+GCO-2303	GCO-231203	243	791	dia 100	0.16	0.3%	2850
GCO-2312+GCO-2304	GCO-231204	231	764	dia 100	0.11	0.4%	2820
GCO-2312+GCO-2305	GCO-231205	224	749	dia 100	0.08	0.2%	2800
GCO-2312+GCO-2306	GCO-231206	220	738	dia 100	0.06	0.5%	2710
GCO-2301+GCO-2301	GCO-230101	233	533	dia 50	1	0.02%	1490
GCO-2301+GCO-2302	GCO-230102	176	401	dia 50	0.5	0.002%	940
GCO-2301+GCO-2303	GCO-230103	155	353	dia 50	0.32	0.02%	980
GCO-2301+GCO-2304	GCO-230104	144	327	dia 50	0.22	0.03%	900
GCO-2301+GCO-2305	GCO-230105	137	312	dia 50	0.16	0.35%	860
GCO-2301+GCO-2306	GCO-230106	132	300	dia 50	0.12	0.003%	820
GCO-2302+GCO-2302	GCO-230202	119	269	dia 25	1	0.05%	380
GCO-2302+GCO-2303	GCO-230203	98	221	dia 25	0.64	0.02%	350
GCO-2302+GCO-2304	GCO-230204	86	194	dia 25	0.44	0.06%	230
GCO-2302+GCO-2305	GCO-230205	80	180	dia 25	0.32	0.27%	210
GCO-2302+GCO-2306	GCO-230206	75	168	dia 25	0.24	0.01%	210
GCO-2303+GCO-2303	GCO-230303	77	173	dia 16	1	0.01%	210
GCO-2303+GCO-2304	GCO-230304	65	146	dia 16	0.69	0.1%	110
GCO-2303+GCO-2305	GCO-230305	59	132	dia 16	0.5	0.25%	100
GCO-2303+GCO-2306	GCO-230306	54	120	dia 16	0.375	0.004%	90
GCO-2304+GCO-2304	GCO-230404	54	120	dia 11	1	0.01%	80
GCO-2304+GCO-2305	GCO-230405	47	105	dia 11	0.73	0.35%	60
GCO-2304+GCO-2306	GCO-230406	43	94	dia 11	0.55	0.1%	40
GCO-2305+GCO-2305	GCO-230505	41	91	dia 8	1	0.1%	60
GCO-2305+GCO-2306	GCO-230506	36	79	dia 8	0.75	0.02%	40
GCO-2306+GCO-2306	GCO-230606	32	68	dia 8	1	0.02%	30

All dimensions are in mm unless otherwise specified.

Interfaces and CCD adapters

The interfaces setting between the base lenses are listed in Table 2. A stop is built in the interface and aligned to achieve the telecentric effect. CCD adapters specified in figure 2 are provided along with the interfaces. Custom CCD adapters are also available on special request.

Fig. 2: Telecentric Lens System

Example of Application

Assume a 1/2 inch CCD is used to inspect a circular object of 45mm diameter. One can choose a combination as follows. The magnification is 0.16 and its lens total length is about 137mm. A CCD adapter will be offered along with the system:

Front Lens GCO-2301 (object size dia 50mm)

Interface GCO-230105

Back Lens GCO-2305 (Image size dia 8mm)

1/2 inch CCD