Gratings are germanium shadowed carbon replicas made from a 28,800 line per inch diffraction grating. The actual grating spacing is 882 millimicrons. They are supplied mounted on grids as required by the customer. For accurate work, the microscope should be calibrated at each high voltage separately. For each magnification run, the objective current should be set at a suitable reading and the image is brought into focus using the specimen "z" screw.
Photographs of the grating should be taken at the magnifications used for the specimen. The negative of the grating is placed in the enlarger and the enlarger moved up or down until the distance between the lines on the easel is that given by the chart. For example, at 25,000 magnification, the distance between the lines on the easel should be 22.1mm. For accuracy, six lines should be measured or a distance of 132.5mm. Note in measuring lines, the distance from one point to where the pattern is repeated (e.g. left side of line to left side of line or centre to centre) should be taken.
There are several advantages in the use of the grating. It makes an accurate record of the magnification used to be filed with your micrographs. It gives convenient round number magnifications (e.g. 25,000 not 24,485). It makes dark-room enlarging easy and convenient.
|Magnification chart for enlarging|
|Print magnification||1 line on easel (mm)||6 lines on easel (mm)|
Actual spacing of grating is 882µm (28,800LPI)