referring to fig4 in a z sharpening method according to a preferred embodiment of the present invention , the near confocal fluorescence or reflection is conveyed back simultaneously via separate coded channels with the one fiber to photodetectors and the intensity converted to an electric signal . the voltage produced from these other channels can be convolved with the confocal return channel voltage and an on - line single scan sharpened image can be generated . fig4 illustrates the volumes around the gaussian waist from which confocal and near confocal fluorescence originates and how the overlap can be used for voxel sharpening . in this figure are shown the gaussian waist 70 , the fluorescence 72 that goes back into the core of the fiber ( not shown ), the fluorescence 74 a , b that goes into the near confocal channel , and the sharpened voxel 76 ( i . e . where there is no overlap between the ‘ true ’ confocal fluorescence 72 and near confocal fluorescence 74 a , b ). fig5 is a schematic view of an apparatus according to an embodiment of the present invention ( though for simplicity using a long path variable pinhole ). in this embodiment the light 80 from laser 82 passes through beamsplitter 84 and is focussed by lens 86 into the core 98 at the tip 88 of a silicone rubber clad single moded optic fiber 90 . the cladding modes in the glass cladding 92 are internally reflected by the low refractive index silicone rubber 94 but are absorbed by cladding mode stripper 96 . the light is transmitted along the core 98 of the fiber 90 to the end 100 of the fiber 90 , from which it emerges as a beam 102 of low na which is reflected by lens 104 to a beam 106 which is intercepted by lens 108 and focussed through a coverslip 110 to a spot ( or gaussian waist ) 112 within a specimen in the form of a cell 114 on a slide 116 . the light re - emanating from “ focal volume ” of the gaussian waist 112 returning through lens 108 retraverses the same optical path as the excitation light 106 . it is reconverged by lens 104 to enter back into the core 98 of the optic fiber 90 at the end 100 and retraverses the core 98 to the other end 88 at which point it remerges and is collimated by lens 86 . passing to the beamsplitter 84 the beam is reflected by the dichroic or semireflective layer 118 to emerge as a beam 120 which impinges on photomultiplier 122 . the electrical signal from this photomultiplier tube 122 provides the ‘ true ’ confocal data set bitmap information . fluorescence which is generated above 124 or below the focal plane arrives back at lens 104 with a degree of lateral displacement 126 which is proportional to the distance of the light returning body from the focal plane ( gaussian waist 112 ). because of this lateral displacement it is converged to the core 98 at the tip 100 of the fiber 90 at angles which are unable to be carried as bound modes within the core 98 . the light is therefore carried as cladding mode rays 128 and 130 . ray 128 came from a plane which was closer to the gaussian waist 112 than ray 130 . ray 128 is therefore carried as a cladding mode of lower angle than ray 130 . a peltier effect cooler 132 reduces the temperature of an optically absorbing medium 134 surrounding the fiber 90 and also cools the silicone rubber and the glass in that vicinity 136 . the silicone rubber has its refractive index increased by the cooling ( relative to the silica ) and the critical angle at the interface 138 will no longer guide the higher angle ray . ray 130 therefore passes through the silicone rubber and is absorbed at 140 . ray 128 which is carried by the fiber 90 at a shallower glancing angle passes through area 136 and proceeds to area 142 where the fiber 90 is cooled by a second peltier effect device 144 , operated at a temperature that is lower than that of the first peltier device 132 . this then allows the light to escape from the glass into the silicone rubber at 146 where it can proceed into a second fiber 148 . the light then proceeds along this fiber to the tip 150 from which it emerges and impinges on the photosensitive surface of a photomultiplier tube 152 . it is desirable that all cladding mode light is extracted and directed to this photomultiplier tube 152 . the electrical output from photomultiplier tube 152 quantifies the intensity of this light . the two temperatures of the peltier effect devices 132 and 144 can be varied to control the mode fraction which passes to photomultiplier tube 152 . fig6 illustrates a variation of the embodiment of fig5 in which two photomultipliers 160 and 162 are used in conjunction with three peltier coolers 164 , 166 and 168 . the temperature of the peltier coolers is t ( p 164 )& lt ; t ( p 166 )& lt ; t ( p 168 ). the principle of operation is similar to the embodiment of fig5 except that light from two separate successive planes above and below the focal plane is sampled by the two photomultiplier tubes 160 and 162 , as follows . fig7 indicates the areas ( representing volumes ) within the gaussian waist 170 from which the sets of modes going to the photomultiplier tubes 160 and 162 of the embodiment of fig6 are derived . photomultiplier tube 160 derives light from the areas 174 a , b corresponding to the lowest order modes , while photomultiplier tube 162 derives light from the areas 174 a , b corresponding to the next set of modes . in carrying out the analog computation a portion of the output from photomultiplier tube 160 is subtracted from the ‘ true ’ confocal signal from area 176 ( from photomultiplier tube 122 ), which effectively removes the signal from the overlap areas 178 a , b and thereby reduces the depth of field of the image obtained . a smaller fraction of the output of photomultiplier tube 162 is added to the ‘ true ’ confocal signal from area 176 , to sharpen the overlap areas 180 a , b . the temperatures of the three peltier effect coolers 164 , 166 and 168 are optimized to give a best sharpening effect . fig8 illustrates the change which would be made to convert the system into a conventional variable pinhole lscm . the cladding mode coupler fiber 182 is relocated from photomultiplier tube 160 and its output is allowed to fall on photomultiplier tube 122 . electrical output addition of the two photomultiplier signals is also possible . the above approach can also be employed to provide a method and apparatus by again utilising the return light from the regions which are slightly out of focus of a reading lens . according to the method of this embodiment , a part of the signal from these slightly out of focus regions is convolved or subtracted from the signal which has been generated by the confocal return light . the separation of the “ near confocal ” return light from the “ true ” confocal return is achieved using modes in an optical fiber . fig9 is a schematic representation of a data reading apparatus according to this embodiment of the invention , in which laser 210 generates laser beam 212 , which is focussed by lens 214 into single mode optic fiber 216 . the light 212 exits fiber 216 , is collimated by lens 218 and directed into beam splitter 220 . one portion of the light 212 is focussed by lens 222 onto digital data storage medium 224 ; the interrogated spot lies at focal point 226 . return light from a digital data storage medium 224 is directed by beam splitter 220 to mirror 228 , which directs the light through beam compressor 230 ( including lenses 232 a and 232 a ). both true confocal rays 234 and near confocal rays 236 emerging from the beam compressor 230 are focussed by lens 238 into silica multimode fiber 242 , encased in low refractive index silicone cladding 240 . towards the end of fiber 242 , higher ( relative to cladding 240 ) refractive index cladding 244 strips out higher order modes ; the remainder of the light ( confocal return light 246 ) is detected by photodetector 248 , which the higher order modes ( near confocal return light 250 ) is detected by photodetector 252 . note that this method can operate in reflected light or in fluorescence mode , and in single photon ( linear ) mode or in non linear ( multiphoton molecular fluorescence ) mode . the method can be used with the one fiber delivering the laser light and returning the signal or with a separate fiber returning the signal ( see fig9 ). it can be made to operated in reflection ( the preferred mode , as depicted in fig9 ) or in transmission . fig1 depicts an alternative embodiment , which can be used to obtain “ unsharp masking ” data density improvement . in this figure , laser light from blue laser diode 260 is collimated by lens 262 into beam splitter 264 . a portion of the light is focussed by lens 266 onto data storage medium 268 ( as above ). return light is directed by beam splitter 264 through beam compressor 270 ; then , both true confocal light 272 and near confocal light 274 are focussed by lens 276 into silica fiber 278 . again , confocal return light exits fiber 278 and is detected by photodetector 282 , while higher modes are stripped out by higher refractive index cladding 280 and detected by photodetector 284 . in this way , “ unsharp masking ” data density improvement can be obtained by subtracting a part of the output of photodetector 284 from the output of photodetector 282 . fig1 depicts an apparatus for use with the apparatuses of fig9 and 10 , for compensating for spherical aberration on focussing into the optical data storage medium or material . in this figure , light from optical data storage medium 290 passes through glass optical wedge 292 ; the optical data is then “ read ” by lens 294 . as the focussed “ reading ” spot 296 moves deeper into the medium 290 , the wedge 292 is moved to the left ( in this view ) so that a thinner portion of wedge 292 is in the beam path , thereby keeping the optical path effectively constant . modifications within the spirit and scope of the invention may readily be effected by persons skilled in the art , so it is to be understood that this invention is not limited to the particular embodiments described by way of example hereinabove . for example , it should particularly be noted that any reference to microscopy or to endoscopy is intended also to refer to endomicroscopy .