Designs for high performance PAL-basedimaging systemsDong Hui,1.*Mei Zhang,"Zheng Geng,'Yunfang Zhang,2 Jingyuan Duan,2 Ancun Shi,2Li Hui,2 Qing Fang,2 and Yuliang Liu?'State Key Laboratory of Management and Control for Complex Systems,Institute of Automation,Chinese Academy of Sciences,Beijing.ChinaOptoelectronic System Laboratory,Institute of Semiconductors,Chinese Academy of Sciences,Beijing,ChinaCorresponding author:donghui1230@gmail.comReceived 11 May 2012:revised 22 June 2012:accepted 23 June 2012:posted 27 June 2012 (Doc.ID 168251):published 20 July 2012In this study,we investigate methods to optimize the design of a panoramic annular lens (PAL)system.with a PAL attachment,and a PAL endoscope system are described.All these designs are optimized usinga standard optical software package (Zemax).The results combine very good image quality with a mod-ulation transfer function above 0.3,which is within the cutoff frequency of sensor chips.2012 OpticalSociety of America0 CIS code8:220.3620,120.4570.1.IntroductionPAL cameras [10-17].However,many existingPanoramic annular lens (PAL)designs have advan-designs have never been presented systematicallytages over traditional wide field of view (FOV)opticalin their entirety.lens designs.They provide panoramic views,areIn this study,we investigate several methods forsimple to fabricate,are compact,and have sharpdesigning PAL-based imaging systems.The designimaging quality.These features make PAL designsdetails are described for a PAL surveillance system,valuable in many applications,such as video surveil-a phone camera with a PAL attachment,and a PALlance systems [1-4],phone cameras,and endoscopicendoscope system.All these designs are optimizedmeasurements.using a standard optical design software packageIn 1986,Greguss et al.proposed a design for the(Zemax).They achieve very good image quality andpanoramic imaging block that is now known as PALthey all have a modulation transfer function (MTF)[5].Since then,researchers have improved many as-above 0.3,which is within the cutoff frequency ofpects of the PAL design.For example,good imagingCCD/complementary metal-oxide semiconductorperformance can be achieved in a PAL system by em-(CMOS)sensors.Generally,a PAL system is com-ploying spherical surfaces [6].In 1995,researchersposed of two components,the PAL block and a relayestablished an analytical representation of PAL thatlens.In this study,we designed a PAL block withcan map characteristics from object to image [7].Thehigh optical performance,easy manufacturability,use of PAL arrangements and image processingand low cost.As this PAL block produces annularin surveillance systems has also been studied [8,9].More recently,some studies have focused on theimage mapping,a simplified relay lens system canoptical design of PAL systems and the products ofachieve adequate imaging quality.According to ourdesign analysis,a cemented doublet lens is the pre-ferred choice,as it creates a relay lens with a compact1559-128XW12215310-08815.00/0size and that can effectively balance aberrations.All2012 Optical Society of Americathe optical design details are described here.5310APPLIED OPTICS Vol.51,No.21 /20 July 2012哭BPAL blockRelay lensFig.3.(Color online)Structureofa PALsurveillance system.TheBlind areadifferent colors represent the different FOVs,which are 52,7080°，90°，100°，and1080corrects and balances aberrations of the PAL block.Fig.1.A PAL systemFinally,the rays form an annular image on a CCD/CMOS sensor.This outline of the optical path is also a brief sum-mary of a PAL system design.The virtual image isformed inside the PAL block.The relay lens changesthe virtual image into a real image and condensesthe image height to match the sensor.When usingannular imaging,spherical and other longitudinalaberrations are not significant and do not need tobe corrected.Lateral aberrations,such as coma,lat-eral chromatic,and others,are major factors in ima-ging quality.If the PAL system is regarded as the-6 lens,relative distortion can be expressed asFig.2.Telecentric PAL block.tan -0DT=-×100%(1)2.PAL Optics and Design SchemeFigure 1 shows the characteristics of a PAL system.For wide-angle lens systems,distortion is one ofThe PAL's cylindrical object space has a vertical fieldthe most significant characteristics affecting theangle B that has rotational symmetry around the op-output image mapping.Because of the relations be-tical axis,which is the z axis in the system.The areatween distortion and pupil aberrations,appropri-from a to the z axis is a blind space that is not en-ately choosing the pupil position benefits distortiongaged in imaging.The PAL block consists of two re-control.Some studies have shown that a telecentricfractive and two reflective surfaces.The optical pathsystem (in which the exit pupil is located at infinity)can be described in the following way.Rays leavingcorrects pupil aberrations [18]and provides otherthe object are refracted into the PAL block from sur-face 1 and reflected off the rear mirrored surface 2.Table 2.Design Data for the Surveillance SystemThen they travel forward in the lens and contact thefront mirrored surface 3.Reflected back,the rays exitRadius ofSurfacethe PAL block from the rear surface 4.After leavingSurface No.Curvature/mmSeparation/mmGlassthe PAL,the divergent rays enter a relay lens that138.2225.78K92-17.54-23.39MIRRORTable 1.PAL-Based System Design Scheme-48.6423.39MIRROR4-17.540.72PAL-Based System Design-6.011.50ZF16-10.049.75PAL BlockRelay Lens7Infinity0.10Set up initial structureSet up initial structure7.022.30BAK41.Doublet lens is preferred9-3.931.50LAK32.Reasonable structure2.Aberrations are considered10-7.551.003.Aperture stop location114.542.00K94.Telecentric system12-6401.40ZF4Combining/Optimizing137.033.14Analysis imaging quality15Infinity0.80K920 July 2012 Vol.51,No.21 APPLIED OPTICS5311110.00100.5FIELD25RMS RADUS:257067.5135(a)(b)FIELO CURVRTURE1.00.50.100.000.10-100.0010108MILLIMETERSPERCENTFIELD CURVATURE/F-THETR DISTORTION(d)Fig.4.(Color online)Graphic report of the PALsurveillance system:(a)MTF diagram,(b)spot diagram,(c)relative curvature/distortiondiagram,and (d)relative illumination diagram.advantages for panoramic systems [19,20].In theory,length of-0.96mm,f/2.0,a52°~108°×360°F0V,the telecentric PAL block is designed so that the en-and a 0.486 gm-0.656 um spectral range.All thetrance pupil coincides with the focal plane of the PALsurfaces are spherical.The diameter of the PAL blockblock.In the actual design process,the center of theis about 60 mm.The total length is 55 mm.We as-entrance pupil is not precisely located at the focus ofsume the image falls on the 1/3"CCD with a pixel sizethe PAL block,but near to it.Figure 2 shows the tele-of 4.2 um.centric PAL block in our demonstration designs.ThisTo satisfy the requirement of a telecentric PALstructure is easily fabricated and can provide highblock,the entrance pupil position is 10.89 mmimaging quality.In this design,the reflective surfaceand the focal length is 11.50 mm.For a PAL used2 and refractive surface 4 are made into one surface.over a broad spectrum,the relay lens needs to beas shown in Fig.2.The value of the radius of the cur-vature of the reflective surface 2 is equal to the valueof the radius of curvature of refractive surface 4.Table 1 summarizes the key points in this PAL-based system design scheme.To demonstrate thesebasic principles,the details of four different success-ful design examples are described below.As a baseline PAL optical design,Fig.3 shows thestructure of a PAL surveillance system with a focalFig.6.(Color online)Structure of an anamorphic PAL surveil-Fig.5.(Coloronline)PAL image mapping:(a)PAL annular imagelance system.The different colors represent the different FOVs,and (b)PAL anamorphic annular image.which are 55,80,and 108.5312APPLIED OPTICS/Vol.51,No.21 /20 July 2012