Magnification and resolution how to calculate size and magnification from an image of an object how to calculate size and magnification from an image of an object

Magnification How many times bigger an object appears on an image of that object when using an optical instrument. How many times bigger an object appears on an image of that object when using an optical instrument. Description of magnification and its calculation from eyepiece and objective lenses Virtual magnifier

The ability to reproduce detail is known as the RESOLVING POWER or RESOLUTION of the system being used Resolution is defined as the smallest distance between two particles which allows them to be distinguished from one another The unaided human eye has a resolving power of about 0.1mm – it can just distinguish between two lines separated by 0.1mm Objects closer together than 0.1mm cannot be distinguished and appear as ONE OBJECTResolution

Light micrograph TEM micrograph Improved resolution in the TEM allows your to Distinguish the membrane systems in cells

Electron micrographs and photomicrographs show specimens that have been magnified to different extents In order to gain a sense of proportion and size from such images, it is necessary to be able to interpret magnification data and scale lines drawn on the image Magnification is a value that tells us how much larger an image is when compared to the original object Magnification = size of image size of object Both values must be converted to the same units before the magnification is calculated If an image measures 30 mm and the specimen or object measures 3  m then the image value must first be converted to  m 30 mm = 30,000  m So, magnification = 30,000 3 = 10,000 Magnification calculations

The ACTUAL SIZE of an object can be calculated using the same formula: Magnification = size of image size of object THEREFORE: Size of object = size of image magnification If an image is measured and found to have a length of 6 mm (6,000  m) and the magnification is 40,000 then: Actual size of object = 6,000 40,000 = 0.15  m Magnification calculations Image ObjectMag

The magnification value of x6,000 can be used to determine the actual dimensions of structures represented in the micrograph When the diameter of the red cell is measured with a ruler it is found to be 42 mm (42,000  m) The actual diameter of the red blood cell is therefore: size of image magnification 42,000 6,000 = 7  m

Actual length of sarcomere = 130,000 75,000 = 1.73  m This electron micrograph of a longitudinal section of skeletal muscle shows the myofibrils and Z-lines of the sarcomeres (magnification x75,000) Courtesy of Dr. H. Huddart – Department of Biological Sciences, The University of Lancaster Z line We wish to know the actual length of the Sarcomere, i.e. the distance from one Z-line to the next A ruler is used to measure the length of a sarcomere in millimetres This distance is found to be 130 mm (130,000  m) USING THE FORMULA: Size of object = size of image magnification Magnification and electron micrographs

The magnification can also be determined from scale lines drawn on images Magnification = length of scale line measured length of scale line given The scale line given on this image has a value of 5  m When this line is measured with a ruler, it is found to have a length of 30 mm (30,000  m) THEREFORE: Magnification = 30,000 5 = 6,000 Magnification and scales Link to interactive magnification Calculation activity using FOV technique (Field of view)