Difference between revisions of "Rangefinder (device)"

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A coupled [[rangefinder]] is a focusing device for rangefinder cameras. Unlike an uncoupled rangefinder, which only tells you how far away you are from a subject, the coupled rangefinder lets you visually focus the camera on a subject.
 
A coupled [[rangefinder]] is a focusing device for rangefinder cameras. Unlike an uncoupled rangefinder, which only tells you how far away you are from a subject, the coupled rangefinder lets you visually focus the camera on a subject.
  
The diagram below shows how it works. The rangefinder is a '''coincident focusing device''', which displays two separate images. The main image is the entire frame of the viewfinder, while the secondary image is a small spot in the center of the frame. To focus on something, you aim the spot in the center at that something, which shows the two images. By turning the focus adjustment, you move the secondary image horizontally until it coincides with the main image. At this point, the camera will be focused on the selected object.
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The diagram here shows how it works. The rangefinder is a '''coincident focusing device''', which displays two separate images. The main image is the entire frame of the viewfinder, while the secondary image is a small spot in the center of the frame. To focus on something, you aim the spot in the center at that something, which shows the two images. By turning the focus adjustment, you move the secondary image horizontally until it coincides with the main image. At this point, the camera will be focused on the selected object.
  
 
The rangefinder works by splitting the image you see into two parts, using a '''beamsplitter'''. This is a prism or a mirror which is "half-silvered", so that about half the light goes straight through it and the othe half is reflected from it. The reflected path is aimed at another mirror which is on a rotating mount. This mount is coupled to the lens's focusing mechanism by a linkage, so that as you focus, the mirror rotates a very small amount. This causes the optical path to sweep left and right, which "moves" the secondary image.
 
The rangefinder works by splitting the image you see into two parts, using a '''beamsplitter'''. This is a prism or a mirror which is "half-silvered", so that about half the light goes straight through it and the othe half is reflected from it. The reflected path is aimed at another mirror which is on a rotating mount. This mount is coupled to the lens's focusing mechanism by a linkage, so that as you focus, the mirror rotates a very small amount. This causes the optical path to sweep left and right, which "moves" the secondary image.
  
 
Rangefinders are very accurate focusing devices, actually more accurate than through-the lens focusing screens on SLRs. Unfortunately, they suffer from [[parallax]] problems, where the framing of the scene through the viewfinder doesn't match that of the taking lens at close distances.
 
Rangefinders are very accurate focusing devices, actually more accurate than through-the lens focusing screens on SLRs. Unfortunately, they suffer from [[parallax]] problems, where the framing of the scene through the viewfinder doesn't match that of the taking lens at close distances.
 
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{{glossary}}
 
{{glossary}}

Revision as of 20:01, 28 February 2006

105615085_d6709d8ce0_o.jpg

A coupled rangefinder is a focusing device for rangefinder cameras. Unlike an uncoupled rangefinder, which only tells you how far away you are from a subject, the coupled rangefinder lets you visually focus the camera on a subject.

The diagram here shows how it works. The rangefinder is a coincident focusing device, which displays two separate images. The main image is the entire frame of the viewfinder, while the secondary image is a small spot in the center of the frame. To focus on something, you aim the spot in the center at that something, which shows the two images. By turning the focus adjustment, you move the secondary image horizontally until it coincides with the main image. At this point, the camera will be focused on the selected object.

The rangefinder works by splitting the image you see into two parts, using a beamsplitter. This is a prism or a mirror which is "half-silvered", so that about half the light goes straight through it and the othe half is reflected from it. The reflected path is aimed at another mirror which is on a rotating mount. This mount is coupled to the lens's focusing mechanism by a linkage, so that as you focus, the mirror rotates a very small amount. This causes the optical path to sweep left and right, which "moves" the secondary image.

Rangefinders are very accurate focusing devices, actually more accurate than through-the lens focusing screens on SLRs. Unfortunately, they suffer from parallax problems, where the framing of the scene through the viewfinder doesn't match that of the taking lens at close distances.

Glossary Terms