While developing deformable mirrors for adaptive optics, and while studying scintillations, we also tested the method of curvature sensing and different variants of it. By very carefully adjusting the optics we were able to discern variations on the scale of one nanometer. The limited dynamic range of the detectors and various optical artifacts caused systematic and random errors of 5 - 8 percent. Calibration of the measurements turned out to be a difficult issue as well. One of the main problems with non-atmospheric measurements was vignetting. We suspect that strong atmospheric scintillation might cause similar problems in curvature sensing, because of light scattered outside the measurement aperture, leading to errors in the estimated wave front phase. We looked into measuring turbulence along the optical path, by comparing field data of both Hartmann- Shack and intensity sensors collected under similar conditions. It seems that some of the turbulence can be tracked back to its range, but this is still being tested. If so, it might be possible to correct it using multi- conjugate optics and reduce significantly scintillation effects. Scintillation can also be removed artificially by correcting a scaled-up version of the turbulence at a scaled-down conjugate distance and vice versa.