A boat seat is mounted on two sets of slidably engaged members for slidably adjusting the location of the boat seat front and back with a locking mechanism for holding the seat at its adjusted location comprising a locking pin for engaging detent holes controlled by a lever arm extending out the front of and below the boat seat. Electrical energy applied to the cathode causes it to reach a sufficiently high temperature to emit a beam of electrons that propagate through the cap beam aperture. The contact portion extends from the first end or the second end of the elongated central portion. A diverter or barrier plate may be carried by the housing cover to extend into the space between the electrodes when the cover is closed, the lower edge of the barrier being spaced from the housing floor a limited distance to force a target animal to squeeze under the barrier as it passes to the second electrode making escape before electrocution difficult. This invention can allow real time imaging of a lens as it accommodates and can better enable researchers and ophthalmic surgeons to develop, fit, implant and diagnose performance of artificial lenses including accommodative lenses.