With findContours I just get no results. Just a Line on the outside of the picture. Also I don’t see any parameters to change in findContours. With the Blob detection at least I get some results 
At the moment the lighting isn’t that good because the other end of the fiber is open and not exactly cut off. In the end use it will be better. But we need to find single fibers like that. For this reason I would like to detect such fibers also. The “good” ones don’t seem to be a problem.