relative pose between two images

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Is it possible to get a relative pose between two images?

When I got E => (R, t) and K shouldn't it be possible to calculate the location of a point in the second image, found in the first image.

I know you need to know the scale factor for full reconstruction but do I really need it two if I just want a relative pose.

And lets say when there is only a rotation then a least the scaling factor should not be interesting?! but why does it then be in this formula with R combined? s2* m'2 = R * s1 * m'1 + t