What's the difference between a rangefinder and SLR?

Question

I've seen rangefinder cameras around and idly wondered what the difference was between them and SLR cameras. Are there any advantages rangefinders offer that cannot be reproduced using an SLR?

Answer 1

A SLR camera allows you to look through the lens and was created to reach WYSIWYG (What You See Is What You Get). It has a mirror box inside, and as a result, is much larger. Other developments include splitting the beam for auto-focus, etc.

A rangefinder is a camera that has a rangefinder mechanism. This is a device that measures subject distance. Through this device, you see two images. When the two images coincide through moving the dial, the correct distance is displayed. On older cameras, this was a separate device and one must transfer this to the lens. Now they are built into the viewfinder. You have different viewfinders for different focal lengths (zoom lenses are difficult, as a result)

Advantages:

• body size/weight
• discreetness
• no mirror blackout, mirror sound, mirror induced vibrations
• shorter registration distance: smaller/lighter lenses, higher quality wide angles
• ease of both-eye-open photography and awareness

Disadvantages:

• lack of auto-focus (though some have contrast-detect AF, but it is no phase-detect)
• parallax effect, pronounced at close differences
• no depth-of-field preview, exact framing, and other WYSIWYG things
• switching viewfinders

Answer 2

The basic difference is that a rangefinder has some kind of contraption to measure the distance (i.e., range) to the subject and then set the focus to that distance, while the SLR uses direct observation through the lens (either with phase detect autofocus or a manual focusing screen) to set the focus. Wikipedia has decent writeups: rangefinder, SLR.

Advantages of the SLR format:

• You look through the same lens that will take the photo, so the composition seen in the viewfinder will match exactly what goes on the film. In particular, there's no parallax error.
• Rangefinders have no feedback loop in the focusing mechanism, so if e.g. the distance scale on the lens becomes miscalibrated, then the camera won't focus right. At a general level, it's very difficult to calibrate rangefinders for good focusing.
• Any filters are in the light path for both the sensor and the viewfinder, so again what's in the viewfinder matches better what will be captured.

Advantages of the rangefinder format:

• No second light path for the viewfinder yields a simpler light path and a smaller, lighter camera.
• No mirror slap: quieter, and no vibrations from the mirror.
• Viewfinder typically shows what will be captured plus lots extra, which many people find useful for composition.

Answer 3

With rangefinders, you compose the shot using a separate viewfinder, rather than with through-the-lens view.

^{Leica M6, photo by E. Wetzig}

This has several implications:

• rangefinder cameras can be smaller than SLRs, since they don't need the space for mirror and prism
• they also can be quieter, cause they don't need to move the mirror in order to take a shot
• you don't exactly see what the lens is going to capture, especially on close distances
• you can't check exact focus and have to rely on distance scale
• you can't check what depth of field is the final image going to have
• when you have interchangeble lenses, you have switch the viewfinder to cover properly the field of view of each lens

Answer 4

A rangefinder is simply a mechanism to measure the distance to an object. Early models came as accessories to cameras, then was incorporated into the viewfinder of the camera.

A rangefinder camera is a camera with a built in rangefinder, which today is synonymous with a camera with a viewfinder. So, what you are asking is really the difference between a viewfinder camera and an SLR:

A viewfinder is separate from the lens, often with much simpler optics, so you see how much you will get in the image, but not exactly how it will look. As the viewfinder is offset from the lens, you get a difference from what you see and the result the closer you get, so closeups can be difficult.

An SLR uses the lens for the view, so you get a better view of what the image will actually look like. Common nowadays is a matte focusing screen that even let you see the depth of focus you get.

The viewfinder camera still has some advantages though. As there is no mirror, it's quieter and smaller, which is useful for some applications.