Rangefinder question for a not-expert

Started Aug 23, 2013 | Discussions thread
bosjohn Veteran Member • Posts: 4,890
Re: Rangefinder question for a not-expert

docvale wrote:

Hi Folks,

I have some questions about the rangefinder mechanism (that I've never used, so far). How does it work exactly? Is it that different from an optical viewfinder? When you're adjusting the aperture on your lens, is there any change on the rangefinder?

Thanks in advance

your range finder is an optical device which will measure distances from your camera position to your subject. When well designed and well made they can be sufficiently accurate for photographic purposes.

you can find many discriptions of how the range finder works on line but essentially it uses prisms and mirrors to allow two separate windows to see the subject at the same time and it uses triangulation to measure the distance. the distance apart the two windows are and the magnification of the eye piece will determin how accurate the device will be,

in the leica the rangefinder can be used in two ways or a combination there of ,When you look through the eye peice on the me camera your using the view finder, on this camera and many others the range finder uses the view finder for one of its windows. In the center of the view finder you will see a rectangle patch that is lighter then its surroundings. This is the range finder patch. if you turn the  focusing lever on your  lens and observe the patch you will see two images of the same scene which will move closer together or further apart. when the two images are alighn so you only see one your in focus. this we call coincidence rangefinding. both the top and bottom edge of your range finder patech are carefully machended so  the line between is quite sharp you can use the top or bottom then in what we call split image method. that is a vreical straight line lines up from inside to outside the range finder patch.  This method will achieve slightly more accurace but it requires some straitht or almost straight lines in your view.

range finder focus is the same accuracy for any lens on the camera and in the case of the Leica there is no connection  to the aperature setting.  Because the accuracy of the same regardless of the lens on the camera it means that the wider angle the lens is the easier it get the focus right, the longer the lenses the more the range finder will be taxed to find good focue becase the depth of fields will be narrower and narrower.  and a fast and long lens push it to the limit/

the main reason Leits and now Leica doesnt offer very long lenses for range finder focusing is do to the above.

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bosjohn aka John Shick bosjohn@yahoo.com

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