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M7 and Parallax Correction


hrahman9

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Reading over the specifications of my M7 (my first rangefinder purchased only recently), it states that the camera automatically corrects for parallax, which I always understood as the bright-line frame in the viewfinder eventually covers the same segment of the subject that the lens does.

 

Is my understanding correct? For subjects that are up close (but within the focus range of the lens), I still see the distortion in the "focus box". Is this normal?

 

I am new to rangefinders, but thought that I would not see any parallax distortion on this camera in the viewfinder.

 

Thanks!

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The framelines in the M7 move down and to the right as you focus, to compensate for parallax error at closer focussing distances. It will never be perfect, but it is pretty close. I'm not sure what you mean by "parallax distortion" though...?

 

Regards,

 

Bill

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Yes, the correction is for the external parallax., i.e. the difference between the 'point of views' of the finder and the lens--which are of course at some distance from each other.

 

Hold up the camera to your eye and look through the finder at a distant subject. Without removing your eye from the finder, or moving the camera, change the focus setting of the lens from infinity to narest focus. You will see how the entire bright frame assembly, the rangefinder patch and the shutter speed display (it it is lit) all move diagonally from northwest to southeast.

 

The old man from the Age of Scale Focusing

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There is a (very) little distortion in the viewfinder (virtual) image, in fact the frameline masks are slightly barrel shaped in reality so they appear square when looked at. This will not be on the recorded image. The framelines close up are near enough the same size as the recorded image, at infinity they cover somewhat less so you will always get at least what you see. Its not much, not worth bothering about really.

 

Welcome to the wonderful (if slightly quirky) world of the rangefinder.

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The way to really see this is to mount the camera on a tripod, point the camera at something fiarly close, turn the lens focus ring all the way to infinity and look at the rangefinder patch at your subject. Now turn the focusing ring away from the infinty mark and the patch & frameline will move off what you were originally looking at.

That is the parallax correction at work.

That is one reason working on a tripod with any M camera can be harder then hand held. If you don't already have the lens nearly focused at whatever distance you are working at when you change the focus the framing will change.

I alway leave the camera unlocked on the ball head until I have the lens focused at my subject then frame and lock down the head.

 

This is one thing you don't have to do with a D/SLR.

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I have made a test film for understanding parallax error with 3 different lenses. At around 1.5m focusing distance you photograph what you see within the framelines. At 0.7m focusing distance there is considerable difference between what you see and what is actually photographed. Horizontal lower border is cropped by about 15% whereas h upper border shifts by the same percentage. Similar effects can be observed but to a lesser degree to vertical borders.

 

When the focusing distance is longer than 1.5m nothing is cropped, actual photo comes up as if it is photographed with a lens that is slightly more wide angel when compared to what you see within the framelines.

 

At or above 1.5m focusing distance nothing is cropped. But you may have a larger covering. At shortest focusing distance ( 0.7m ) you must take into account the uncorrected parallax. You have to compensate for what you see in the framelines for uncorrected parallax when composing.

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