This combination C mount and relay lens works to couple a microscope camera to a microscope tube for digital image capture. The relay lens is adjustable so that you can focus to the correct focal plane which will allow you to make your microscope parfocal. This allows for the specimen to be in focus when you look through the binocular tube of the microscope as well as when you look at the image screen. The relay lens works to combat inherent magnification which allows you to see a wider field of view on the camera image. This is available in .38x and .55x sizes.