Microscope and Microscopy - A Quick historical Journey of Microscopes-advanced

The journey of microscopy began in the late 16th century (circa $1590$) with Zacharias Janssen and his father Hans, who created the first compound microscope using two convex lenses.

Robert Hooke ($1665$) used a primitive compound microscope to observe thin slices of cork and coined the term 'cell'. His observations were published in the famous book 'Micrographia'.

Antonie van Leeuwenhoek ($1670s$) developed high-quality single-lens (simple) microscopes with magnifications up to $270\times$. He was the first to observe living cells, which he called 'animalcules', including bacteria and protozoa.

Magnification ($M$) is the process of enlarging the apparent size of an object. Total magnification in a compound microscope is the product of the magnification of the objective lens and the ocular (eyepiece) lens.

Resolving Power is the ability of an optical instrument to distinguish two closely placed objects as separate entities. It is inversely proportional to the limit of resolution ($d$).

Ernst Abbe ($1873$) formulated the physical laws governing image formation, introducing the concept of Numerical Aperture ($NA$). He proved that resolution is limited by the wavelength of light ($\lambda$).

The Electron Microscope was co-invented by Ernst Ruska and Max Knoll in $1931$. It uses a beam of electrons instead of light. Since the wavelength of electrons is significantly smaller than that of visible light, it achieves much higher resolution (up to $0.1\ nm$).

Modern microscopy includes specialized techniques like Phase-Contrast Microscopy (to see living, unstained cells), Scanning Electron Microscopy (SEM) for 3D surface imaging, and Transmission Electron Microscopy (TEM) for internal cell structure.