plotting only some error bars

Hoi,

For some plot I'd like to display a dotted line (style = 'k.-') with an error
bar at only every 30th point or so. The error values in this case are
scalars.
Of course, I could produce a slice like mydata[::jumper] and plot these above
the first plot, but this seems a bit akward. Anyone with a better solution
out there?

TIA
Christian