The adapter bridges the gap in flange distance (distance between mount and sensor/film) between the NEX native E-mount (18mm), and the MD/SR mount (43.5mm). Therefore, the focal length of the MD lens isn't affected, it's still at its native flange distance from the sensor.
If you were to adapt an MD lens to a mount with longer flange distance (i.e. canon EF, 44mm), the net effect would be that of an extension tube, equivalent FoV but the focus range would shift, allowing a closer minimum focus (and therefore, increased maximum magnification) but losing the ability to focus on infinity.
However, your FoV IS affected by the APS-C-size sensor in the NEX-5, causing an effective 1.6x crop in FoV (about the same as an 80mm lens in your case).