Selection of the imaging lens for the inspection system

Updated: 2014/06/27

Selection of the imaging lens for the inspection system

In the explanation of the Fresnel lighting inspection system, FLL magnification fixed floating focal lens was introduced for low magnifications, the FLH magnification fixed floating focal lens group for large magnification, and OTH fixed focus lens group for middle magnifications as an imaging lens used for the optical imaging inspection system. And a MTF experimental value and a calculated value when each imaging lens and the corresponding Fresnel illumination system were combined were also introduced by the item of MTF Description of PRODUCT(Illumination). While introducing a new lens group together with these lens groups, we would like to see MTF change of each lens group when imaging magnification is a parameter. When using the same lens or the same lens group in a different magnification generally, since a field angle becomes large so that magnification is small, when the image sensor is the same size, in order to maintain performance, it is necessary to enlarge(darken) the F number to be used. Relationship of F-number and magnification for three series of lens groups, which were introduced in Fresnel lighting inspection system, FLL magnification fixed floating focus lens group, OTH fixed focus lens group, the FLH magnification fixed floating focus lens group are as follows:

FLL lens group  0.12X~0.5X  F/6~F/4.5

OTH lens group  0.3X~1.33X  F/5.6

FLH lens group  1X~3X  F/4.3~F2.3

Although we would like to see the MTF value over the magnification of these three lens groups, it becomes difficult for an OTH lens of low MTF compared with other lens groups, since the F number to the magnification is large(dark) compared with a FLL lens group or a FLH lens group. Therefore, we will add the FLM magnification fixed floating focal lens group for middle magnifications which have an equivalent F number as a FLL lens group or a FLH lens group, and see change of MTF instead of the OTH fixed focus lens group quoted by explanation of the Fresnel lighting inspection system. Relationship of F-number and magnification for the FLM magnification fixed floating focus lens group are as follows: FLM lens group??? 0.5X~2X??????? F/4 In addition, the magnification of each lens group mentioned until now, or mentioned from now on is an example of a typical magnification setup, and it is possible to set up and supply the other specific magnification. Since a FLL lens group, a FLM lens group, and a FLH lens group are a floating focus lens group, fine setting is enabled. (Please contact us for details.) These three lens groups are intended for use of 60mm line sensor of 16K elements with 3.5μm pixel size or 60mm line sensor of 12K elements with 5μm pixel size. In each case, the resolution corresponding to the lens is as follows.

Pixel Size Element Number Sensor Length(nominal) Resolution
5μm 12K 60mm 100lines/mm
3.5μm 16K 60mm 143lines/mm

Table 1 Specification and Resolution of 60mm line sensor

The resolution of an imaging lens is dependent on the usage of the lens and the method of the illumination, but the calculated MTF value of the resolution at the pixel size of the sensor can be used as one standard. Main example of the magnification for 3 lens groups, FLL, FLM, FLH and the size of the object using the 60mm line sensor are as follows.

lens FLL-015x FLL-017x FLL-019x FLL-023x FLL-025x FLL-027x FLL-030x FLL-034x
Mag 0.15 0.1688 0.1875 0.225 0.25 0.2727 0.3 0.3375
Obj 2y 400.00 355.56 320.00 266.67 240.00 220.00 200.00 177.78
lens FLL-037x FLL-045x FLL-050x FLL-054x FLL-060x
Mag 0.375 0.45 0.5 0.5455 0.6
Obj 2y 160.00 133.33 120.00 110.00 100.00
lens FLM-050x FLM-054x FLM-060x FLM-067x FLM-075x FLM-090x FLM-100x FLM-109x
Mag 0.5 0.5455 0.6 0.675 0.75 0.9 1 1.0909
Obj 2y 120.00 110.00 100.00 88.89 80.00 66.67 60.00 55.00
lens FLM-120x FLM-135x FLM-150x FLM-180x FLM-200x
Mag 1.2 1.35 1.5 1.8 2
Obj 2y 50.00 44.44 40.00 33.33 30.00
lens FLH-100x FLH-109x FLH-120x FLH-135x FLH-150x FLH-180x FLH-200x FLH-218x
Mag 1 1.0909 1.2 1.35 1.5 1.8 2 2.1818
Obj 2y 60.00 55.00 50.00 44.44 40.00 33.33 30.00 27.50
lens FLH-240x FLH-270x FLH-300x
Mag 2.4 2.7 3
Obj 2y 25.00 22.22 20.00

Table 2 Size of the object and the magnification of the lens for 60mm line sensor

The MTF at 100 lines/mm using the 5μm element line sensor and 143 lines/mm using the 3.5μm element line sensor for each lens are shown in the figure〔Selection of the lens for inspection system 1〕which horizontal axis is the object size or the magnification. As shown in references at the bottom left of the graph, blue diamond in the upper left is 100 lines/mm and brown□ in the lower left is 143 lines/mm of MTF value for FLL, green△ in the upper center is 100 lines/mm and purple× in the lower center is 143 lines/mm of MTF value for FLM, and skyblue? in the upper right is 100 lines/mm and orange circle in the lower right is 143 lines/mm of MTF for FLL. Magnification in the 1st line and object size in the 2nd line corresponding to the 60mm line sensor are shown on the lower table of the graph.(Magnification and object size are shown similarly under the horizontal axis of MTF0. The value below it is the MTF value corresponding to a graph. ) The 3rd line of the table shows the size(unit μm) of the object corresponding to 5μm element of 12K line sensor, and the 4th line shows the size(unit μm) of the object corresponding to 3.5μm element of 16K line sensor The magnification range of a corresponding lens is as follows as shown in the title portion of the graph. FLL lens group 0.15x – 0.6x for 60mm sensor FLM lens group 0.5x – 2.0x for 60mm sensor FLH lens group 1.0x – 3.0x for 60mm sensor And an upper curve is for 100 lines/mm: 5μm (12K) and lower curve is for 143 lines/mm: 3.5μm (16K) of MTF value at the same magnification range. In addition, clicks near the point where each MTF value is plotted will show these specifications and performances at the magnification of the corresponding lens such as F number, magnification, lens length, focal length, NA, resolution, working distance, total length and optical-path drawing, aberration diagram, chromatic aberration, and detailed MTF diagram If you utilize these graphs and data, you can predict the imaging result and which lens will be the optimal to use. On the other hand, the resolution on the object side is decided by the element number of the line sensor and the magnification of the using lens fundamentally. In fact, the MTF value at that resolution and magnification is further related. Since the MTF value generally become high at lower resolution, that is the case for larger element size sensor, it may be useful to use larger element size of the same element number sensor. In that case, since the line sensor length becomes that much long, if lens magnification is raised a little in order to keep the same image length (MTF changes also with this), the resolution needed with a lens will be small and it can raise a MTF value as a result. As this example, Mejiro Genossen is preparing E2M and E2H lens group for 80mm line sensor of 16K elements with 3.5μm pixel size. The resolution corresponding to the lens is as follows.

Pixel Size Element Number Sensor Length(nominal) Resolution
5μm 16K 80mm 100lines/mm

Table 3 Specification and Resolution of 80mm line sensor

Main example of the magnification for 2 lens groups, E2M, E2H and the size of the object using the 80mm line sensor are as follows.

lens E2M-033x E2M-036x E2M-040x E2M-045x E2M-050x E2M-060x E2M-066x E2M-072x
Mag 0.3333 0.3636 0.4 0.45 0.5 0.6 0.6667 0.7273
Obj 2y 240 220 200 177.78 160 133.33 120 110
lens E2M-080x E2M-080x E2M-090x E2M-120x E2M-33x E2M-145x E2M-160x E2M-180x
Mag 0.8 0.9 1 1.2 1.3333 1.4545 1.6 1.8
Obj 2y 100 88.89 80 66.67 60 55 50 44.44
lens E2M-200x
Mag 2
Obj 2y 40
lens E2H-133x E2H-145x E2H-160x E2H-180x E2H-200x E2H-240x E2H-267x E2H-291x
Mag 1.3333 1.4545 1.6 1.8 2 2.4 2.6667 2.9091
Obj 2y 60 55 50 44.44 40 33.33 30 27.5
lens E2H-320x E2H-360x E2H-400x
Mag 3.2 3.6 4
Obj 2y 25 22.22 20

Table 4 Size of the object and the magnification of the lens for 80mm line sensor

The MTF at 100 lines/mm using the 5μm element 80mm line sensor for each lens are shown in the figure〔Selection of the lens for inspection system 2〕which horizontal axis is the object size. For comparison, the MTF at 143 lines/mm using the 3.5μm element 60mm line sensor for FLL, FLM, FLH lenses are shown in the same graph. As shown in references at the bottom left of the graph, blue diamond in the upper center is 100 lines/mm(80mm) of MTF value for E2M, green△ in the upper right is 100 lines/mm(80mm) of MTF value for E2H and brown□ in the left ,purple× in the lower center, orange circle in the lower right is 143 lines/mm(60mm) of MTF value for each FLM, FLM and FLH. Object size in the 1st line, magnification in the 2nd line corresponding to the 60mm line sensor and magnification in the 4th line corresponding to the 80mm line sensor are shown on the lower table of the graph. In order to make the same objective size, the magnifications for a 60-mm line sensor and an 80-mm line are different. (Object size is shown similarly under the horizontal axis of MTF0. The value below it is the MTF value corresponding to a graph. ) The 3rd line of the table shows the size(unit μm) of the object corresponding to 3.5μm element of 15K line sensor, and the 5th line shows the size(unit μm) of the object corresponding to 5μm element of 16K line sensor

The magnification range of a corresponding lens is as follows as shown in the title portion of the graph. E2M lens group 0.33x – 2.0x for 80mm sensor E2H lens group 1.33x – 4.0x for 80mm sensor And the MTF at 143 lines/mm using the 3.5μm element 16K 60mm line sensor for FLL,FLM,FLH lenses are shown as in the figure[Selection of the lens for inspection system 1] for comparison. In addition, as the figure〔Selection of the lens for inspection system 1〕 ,clicks near the point where each MTF value is plotted will show these specifications, aberration diagram, MTF diagram and etc. We are sure that you can understand the ability of these imaging lenses for 60mm line sensor and 80mm line sensor, and these data will help you to choose proper sensor and proper imaging lens.

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