Split Image Vs. Coincident Image--Same Thing?

What's the difference between split image focusing and coincident

image focusing? Seems like they are one in the same. TIA.

 

Richard

Causing a coincident image assumes starting with two, which would be from a true rangefinder with binocular sense. A split image can occur, as in an SLR, by breaking a line with opposing prisms.

Richard,

 

This confused me, too, when I read it in a Leica user manual. I couldn't see what was the issue, since it seemed so obvious so why mention it? I guess it's just someone at Lecia with a bee in his bonnet!

 

You're right, they're exactly the same except for the way in which you use the rangefinder. With coincident image, you look at two images of the same subject, within the area of the rangefinder patch, and turn the focus ring until they exactly coincide.

 

With split image focusing, you choose a vertical line in the plane of the subject (if you can find one) and observe the discontinuity in the line, caused by the second image, where it crosses the top (or bottom) edge of the RF patch. You turn the focus ring until there is no discontinuity in the line, just as you would with the split image circle that is at the centre of some SLR camera focus screens.

 

Some people find the split image method to be easier and/or more accurate than using the coincident image. I believe that most people, once they are used to the rangefinder, use whichever of these methods suits the circumstances without thinking about it.

There is a difference. Many older rangefinder cameras do not have a hard sharp 'edge' to the rangefinder patch - just a fuzzy yellow (or other color) area where there are two images. Canonet, Canon P, among others.

 

Such cameras cannot 'split' the image since there is no hard edge to split it along - the can only use coincident (overlapping double image) rangefinding.<div></div>

Andy; great examples! With my Russian Lennigrad motor drive LTM camera; the patch is like the first example; BUT the patch does NOT show part of the direct viewed image. This means one focuses with the top and bottom edges of the patch only. The rectangular patch area of the rangefinder blocks out all the direct view. This is abit odd; different than other rangefinder cameras I have used. The rangefinder patch is about 100 percent as bright as the direct view.

Screw-mount Leicas are an example of a coincidence-only rangefinder.

Kalart made a small 21/4 by 31/4 press camera that had a "true" coincident finder. I believe it worked somehow by looking into a black viewfinder with right eye, the left eye looking straight at subject (not through camera), and the projected image from a yet further-to-the-right objective would project the image onto the right eye's black view -- making the (real)left eye image merge with the projected right eye image. I believe it was the only commercial camera made this way, and since the verison I had my hands on didn't work, I may have the principle wrong.

 

But, for all other cameras, the above explanation is close enough.