What is the difference between these types of viewfinders?

Question

Rangefinder, Single Lens Reflex, Electronic, LCD (TTL)

Answer 1

Rangefinder: The view you see is not 'Through The Lens', of the 4 view types this is the only one that isn't. You're looking at a estimated view of what the lens is seeing, it may or may not include guides/crops within the viewfinder to indicate different fields of view. One side benefit of this is there is no mirror between the lens and film to direct light to your eye so no mirror needs to flip up when you take a picture.

Single Lens Reflex: The view you see is 'Through The Lens', a mirror is placed between the lens and film to direct light to your eye for you to view, there may or may not be another mirror or prism to direct the light again (to your eye). The first mirror needs to flip up in order for the photograph to be taken. There will be slight differences between what you see and the sensor actually captures. Canon actually created a film SLR that used two prisms instead of any mirrors to speed up FPS by having no mirror slap, the EOS 1N RS, it got 10FPS.

Electronic Viewfinder: Provides a similar 'viewing style' as SLR but instead of using a mirror and prism to send the light from the lens to your eye a tiny LCD is place in the viewfinder and you're looking at exactly what the sensor is capturing.

LCD Viewfinder: I assume you mean an LCD on the back of the camera, this eschews the viewfinder all together and has a large LCD on the back of the camera that shows exactly what the sensor is seeing. You don't actually need to place your face to the camera.

Answer 2

You already got the exact answer to your question, but I think it is equally important to know what the benefits and issues are with each viewfinder type.

Rangefinder: View is approximate, coverage is incomplete and may be even off-center. No way to preview exposure, white-balance, depth-of-field. May have an indicator of focus but not exact. I don't have much experience here, so it may vary between models.

Single Lens Reflex: (Often called Optical Viewfinder or OVF for short): Shows either a complete (100% coverage) or partial (92-98% coverage) view through the lens, so coverage is always perfectly aligned (edges may be missing for partial coverage) and the focus plane is shown exactly. Usually shows the view at the maximum aperture which means that DOF is exact unless the camera is equipped with a DOF-preview option. Keep in ming that Depth-Of-field is size-depending, so even with the preview there will be differences between the previewed DOF and visible DOF in the final image. An OVF does not preview exposure or white-balance.

Electronic: (Often called EVF): Nearly always shows an exact view of framing (100% coverage). Can (depending on the implementation) preview exposure, white-balance, depth-of-field and focus. Same caveat applies with DOF as with an OVF, it may not be the same in the final image because it is size-dependent. Focus checking is the biggest issue with most EVFs, since their relatively low-resolution is insufficient to show precisely what is in focus. Most EVFs have 200K-240K pixels but a handfull now reach 1.5 megapixels which is much better for focusing. Since the view is electronic, there is a short but sometimes perceptible delay between action and what is seen in the EVF, potentially making it harder to track moving subjects.

LCD: (TTL or Display View): Basically a much bigger version of EVFs. All the viewing properties are the same except that its position make it susceptible to ambient light. So if you are in a very bright area, an LCD may become very hard to view due to reflections.

Optical Tunnel: A parallel lens located near the photographic lens. It usually zooms in sync with the other lens. It shows very coarse (60-85%) and off-center framing. Does not preview anything, no focus, no exposure, no white-balance, etc. Sometimes (as in most Canon G-series), you can see the camera's photographic lens through the optical tunnel. This type of viewfinder is disappearing but was in high-demand when cameras with LCDs only (no OVF or EVF) had poor anti-reflective coatings which gave poor outdoor visibility.

Source: http://www.neocamera.com/article.php?id=viewfinders