A lens free microscope is an optical microscope that does not require a lens to form an image. The first lens free microscope was built in 1873 by Ernst Abbe. In the early years of microscopy, most microscopes were refracting type, which used a lens to bend (refract) light rays to form an image. However, some scientists and engineers began experimenting with other ways to form images, such as using a mirror (reflecting type). In 1873, Ernst Abbe developed the first successful reflecting type microscope, which did not require a lens. His design used a curved mirror to reflect and focus light onto the specimen.
Although Abbe’s design did not use a lens, it still required a medium through which light could travel from the object being viewed to the eye or camera. This medium was typically air, but it could also be water or oil. In the early 1900s, many scientists and engineers began experimenting with different ways to eliminate this medium entirely. One approach was to use X-rays instead of visible light; however, this method had several disadvantages. First, X-rays are harmful to living tissue; second, they are absorbed by many materials, making it difficult to get a clear image; and thirdly, they can only be focused over very short distances. Another approach was developed by German scientist Richard Zsigmondy in 1914. He used Ultraviolet (UV) light instead of visible light or X-rays because UV light can penetrate many materials that absorb visible light or X-rays. To focus the UV light rays without using a lens , he placed them on a concave mirror . Finally , he added an eyepiece so that the user could view the magnified image .
While both of these methods – using X-rays or UV light – had their advantages , they also had significant disadvantages . For example , neither method could be used to view live specimens because both X – rays and UV radiation are harmful to living tissue . Additionally , these methods required specialised equipment that was expensive and difficult to use . As a result , neither method became widely adopted .
In 2006 , two scientists at Stanford University – Wei Xia and Manu Prakash – developed a new way to create images without lenses or mirrors . Their method – called “lensless imaging” – uses what is known as “digital holography.” Digital holography is similar in principleto traditional film holography ; however , instead of using photographic film , digital holography uses computers and digital sensors . This makes it possibleto capture images very quickly – even of moving objects ! Additionally , digitalholography doesn’t require any harmful radiation like X-rays or UVlight ; thus , it can be used safely on live specimens . Finally , since thereis no need for lenses or mirrors , digital holographic microscopes are muchsimpler (and cheaper!) than conventional optical microscopes .
Digitalholographic microscopy works by shining laser light onto both the objectbeing viewed AND onto a reference point nearby . The laserlight reflects off of both the object ANDthe reference pointand then interferes with each other(this interference pattern is recorded by adigital sensor ). By analyzing this interference pattern computationally ,”phase retrieval algorithms” can be used toreconstruct an imageof the object WITHOUT needinga lens!
This technique has already beenused successfullyto study everything from virusesand bacteria topiezoelectric materialsand 3D printing! And becauseit doesn’t require specialised equipmentor harmful radiationsto work effectively , it has great potentialfor widespread adoptionin medical settingsas well as industrialand academic ones !