690. Use Of Mirror To Illuminate The Slide By Transmitted Light

Use Of Mirror To Illuminate The Slide By Transmitted Light. Proper manipulation of the mirror for reflecting light is very important and should always be carefully done, as one may fail to obtain the best results and may be led to reach wrong conclusions. Where strong daylight is used for focusing, the improper use of the mirror may become injurious to the eyes. The mirror of the microscope is double - one side being plain and the other concave. The mirror is provided with a universal joint to reflect the light from any source, either from the front or side of the microscope. The plain mirror is used with low power objectives; while the concave mirror converges the rays on the object and thereby gives intensified illumination; the latter is used with medium and high power objectives. When daylight is employed the concave mirror, converging the light as it does on the object, has a focal point, and this is of such length that with parallel rays it will concentrate on the object.

691. Use Of The Abbe Condenser

Use Of The Abbe Condenser. With artificial light the focus will be longer, as the rays are more diverging, and when no provision is made in the instrument to adjust the mirror to meet these two conditions, it becomes difficult, and sometimes impossible, to obtain the best results in critical work. For this and other advantages, an additional illuminating apparatus, termed an Abbe condenser, is now universally employed with both medium and high power objectives. The purpose of the Abbe condenser is, to give an amplified field of illumination when the illuminant is otherwise insufficient to illuminate the object with a cone of light having an angular aperture equal to that of the objective, as well as to provide the means for controlling the amount and character of the illumination to suit the various conditions of work.

692. This condenser is attached beneath the stage of the microscope and is mounted in a most complete form. (See T, Fig. 1 of Illustration No. 124.) Where the Abbe condenser is used, careful attention must be given to illuminating the object. A good rule to follow is to use concentrated illumination, diaphragming down to as small an opening as will permit of showing the structure and other characteristics of the object.

693. It is also advisable where the Abbe condenser is employed, to use the plain mirror for reflecting the light, and, whether artificial or daylight is employed, the blue screen which is fitted in the Abbe condenser should be used.

694. Plates To Use

Plates To Use. While almost any reliable brand of plates may be employed, yet a very rapid plate is quite difficult to handle, and where ordinary plates are employed the slower emulsion is preferred. For the best results, and in cases where color values are to be preferred, it is absolutely essential that color corrected plates be used, such as orthochromatic, isochromatic or panchromatic. For ordinary subjects where color values are not important the double-coated ortho or non-halation plates will answer.

695. When color sensitive or double-coated plates are not available, slow plates may be used quite satisfactorily and longer exposures given. When orthochromatic plates are employed, care should be exercised in loading the holders, as the plates are very sensitive even to the ruby light, and the holder should be loaded either in total darkness or at a distance from the ruby light; otherwise fogged plates will result.