another example of such a structure is a perforated shell 127 rotationally coupled to the torque cable 28 as shown in fig1 the perforated shell 127 has a delivery aperture 129 to permit light from the delivery fiber 18 to pass through the shell 127 unimpeded and a collection aperture 131 shaped to block a portion of the light incident on the collection mirror 82 in another example shown in fig1 an opaque band 133 on a transparent distal tip 135 of the stationary sheath 26 is positioned to obscure a portion of the collection mirror 82 the band 131 extends circumferentially around the sheath so that the collection mirror 82 is obscured as the torque cable 28 rotates the collection mirror 82 any of the foregoing beam shaping structures can have an edge that is modified to diffract light incident thereon in a manner that causes the field of view to have a pre selected geometry such an edge can be formed by providing protrusions or indentations having a dimension on the order of the wavelength of light to be observed the beam shaping function of the foregoing obstructions can also be achieved by providing an optical system in optical communication with the collection mirror 82 such an optical system can include a collection mirror 82 with a.