| | | To focus the light beam, remove one of the microscope objectives and position the appropriate filter cube in the light path. Using a piece of paper at the microscope, stage as a target, adjust the position of the light guide mount until a sharp image of the end of the light guide is seen at the stage. Centre the image using the offset adjustments on the light guide mount. 2. Replace the microscope objective and check for uniform illumination at the image plane. The illumination path is now fully aligned and the system ready for use. The bulb should last for a long time, but its light output will fall during use because of build-up of material from the electrodes onto the inside of the glass envelope. Much of this decline will occur Over the first few (high-power) flashes, and a figure of 50"i> seems typical. You may therefore wish to use a new bulb for any occasional experiments where the highest possible light intensity is required, but in practice it will be more important that the optical set-up is optimised. Tips on how to do (his arc given in section 5. | | |