Photoadaptors (with reducer lens) for microscopes

 Why is a recuder needed when taking images with a microscope?

Most of the microscopes provide error free image of an area with 18-22mm in diameter, but the typical microscope cameras contain much smaller CMOS sensors. Because the pixel sizes have shunk in recent years, the microscope cameras provide higher magnification, usually 20x-30x. When taking images, usually only a small part of the visible field is captured and this image is also underexposed.
The reducers are available in two different types. One is a projection one (just like a slide projector), whilethe other one is a special concave lens, introduced by Harlow Shapley (Shapley-lens). The reducer in both cases makes the image smaller but more contrasty and vivid. It is a kind of mandatory element when using dark field or fluorescent observations.