Development of Near-Diffraction Limited, Low-Cost and High-Resolution CCD Camera System for Imaging Coulter Orifices: Performance Analysis Using Zemax

Development of Near-Diffraction Limited, Low-Cost and High-Resolution CCD Camera System for Imaging Coulter Orifices: Performance Analysis Using Zemax

Sami D. Alaruri (Independent Scholar, Uniontown, OH, USA)
DOI: 10.4018/IJMTIE.2014040105

Abstract

A low-cost CCD camera system for imaging Coulter orifices ranging in diameter between 20 µm and 2 mm has been developed and tested. The imaging system incorporates a 6X magnifying lens for viewing the required range of Coulter orifices and LEDs (Light emitting diodes) lamp for back illuminating the orifices. Geometric optic calculations using Zemax® for the micro-lens interfaced with the camera suggest that the spot diameter and the MTF spatial frequency at field of view equal to 0 ° and at the image plane are 5.13 µm and 271.6 lines/mm (at contrast= 37.6%), respectively. Images captured with the camera system for 20 µm, 100 µm and 2 mm diameter orifices are provided. Furthermore, a discussion for the camera micro-lens modulation transfer function, spot diagram, root-mean-square wavefront error versus field and optical path difference plots is given.
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2. Experimental Procedure

The Coulter orifices imaging system consists of four major parts: on-board Firewire CCD camera, micro-video lens interfaced with the camera, white LEDs lamp and a 6X magnifying lens.

As depicted in Figure 1, a Firewire IEEE-1394 on-board CCD camera (Edmund Optics, p/N U58-223; pixels: 659x494; pixel size: 5.6 x 5.6 μm; 3.7 mm (H) x 2.8 mm (V); price= $200) equipped with a micro-lens (FL= 25.0 mm, f# 2.5; Field-of-View= 8.5˚; total track= 36.19 mm; price= $64) is used to image the Coulter orifices. A 46.5 mm focal length 6X magnifying lens (Edmund Optics; p/n NT45-585; Focal Length= 46.5 mm; price= $35) was placed between the orifice and the surface of CCD imager at 127 mm distance from the CCD imager. The 6X magnifying lens is mounted on a translational stage (Newport, p/n M-SDS65) which has 15 mm maximum translational distance. The imaging system magnification is adjusted by moving the 6X magnifying lens along the optical axis. The orifice is back illuminated using a white LEDs lamp (Ledtronics, Inc., p/n B618-OCW-0285, price= $30). The LED lamp (487 mcd; Voltage=28 VDC; Current= 15 mA) illumination is set to operate at approximately 90% of the CCD saturation level. Moreover, the camera system is provided with image processing software for viewing and capturing still images.

Figure 1.

Block diagram depicting the Coulter orifices imaging system layout. L1= 26 mm; L2= 20 mm; L3=37 mm; L4= 59 mm; L5= 36.19 mm; L6 maximum range = 15 mm (adjustable); imaging system total track= 178.19 mm.

3. Results And Discussion

Prior to collecting images, four geometric image quality metrics (Geary, 2002) for the micro-lens, namely, MTF (Zhang, 2012; ISO, 2010), spot diagram, RMS wavefront error (WFE) versus field and optical path difference plots were evaluated using Zemax.

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