Magnification Calculation

Formula

(Photo eye-piece) x (Camera factor) x (Objective) x (Enlargement)

Example:

• A photograph has come back to you that you took with a 40 x objective.
  
  
• The image dimensions are: 126 mm x 84 mm (l x h)

The enlargement convention is based on linear measurement not area thus is in this case the photo length (or width) divided by the negative length (or width); in this case the negative is 35 mm film ie 36 x 24 mm; 126 ÷ 36 = an enlargement of 3.5

To calculate the magnification of a photograph taken on the Zeiss Fluorescence Microscope

10 (fixed) x 0.25 (fixed) x 40 (objective) x 3.5 (enlargement) = 350 x mag

To calculate the magnification of a photograph taken on the Leica Fluorescence or Leitz Light Microscope

8 (fixed) x 0.32 (fixed) x 40 (objective) x 3.5 (enlargement) = 358 x mag

Addendum

With the advent of digital images, the size displayed depends on the viewing medium. Monitors are usually 72 dpi across the screen area. They also come in different screen sizes and have various display resolutions denoted by pixel dimensions eg 800 x 600, 1024 x 768. Even on one monitor an image can be displayed at various apparent sizes; further software will often scale to fit. Web images are 72 or 96 dpi which is best for screen viewing and small in file size, however lower in resolution. When printing, DPI refers to print resolution or image complexity/density and will depend not on the size on the screen but on the output on the printing device. Magnification is thus variable and not so useful as a visual assessment tool. A scale bar is of far more value and will change with the image display whilst still representing the measurement of a specimen.