Glossay fo Camera Types and Photography Technology. What is a RangefinderA rangefinder is a focus mechanism that allows the user to calculate the distance of a subject through the convergence of two images. Cameras that use this mechanism are usually referred to as ‘rangefinders’. Rangefinder cameras were very popular in the 1950s, 60s and 70s. Single Lens Reflex (SLRs) and compact cameras largely replaced them in the 70s, 80s and 90s. What is not always appreciated is that rangefinders offer several tangible benefits over SLRs, not least in image quality. Indeed, many photographers would rate the Leica M Digital Rangefinder as one of the best cameras available today.      and DSLRA digital single-lens reflex camera (digital SLR or DSLR) is a digital camera that combines the optics and the mechanisms of a single-lens reflex (SLR) camera with a digital imaging sensor. The reflex design scheme is the primary difference between a DSLR and other digital cameras. In the reflex design, light travels through the lens and then to a mirror that alternates to send the image to either the viewfinder or the image sensor. The viewfinder of a DSLR presents an image that will not differ substantially from what is captured by the camera's sensor but presents it as a direct optical view through the lens, rather than being captured by the camera's image sensor and displayed by a digital screen. DSLR is often (wrongly) used to describe cameras that are Micro Four Thirds or Bridge Camera  - just because they look similar. This can bee seen when cameras are offered for sale.   .