A southern hemisphere survey of the 5780 and 6284 {\AA} diffuse
  interstellar bands: correlation with the extinction
  We present a new database of 5780.5 and 6283.8 {\AA} DIB measurements and
also study their correlation with the reddening. The database is based on
high-resolution, high-quality spectra of early-type nearby stars located in the
southern hemisphere at an average distance of 300 pc. Equivalent widths of the
two DIBs were determined by means of a realistic continuum fitting and
synthetic atmospheric transmissions. For all stars that possess a precise
measurement of their color excess, we compare the DIBs and the extinction. We
find average linear relationships of the DIBS and the color excess that agree
well with those of a previous survey of northern hemisphere stars closer than
550 pc. This similarity shows that there is no significant spatial dependence
of the average relationship in the solar neighborhood within $\simeq$ 600 pc. A
noticeably different result is our higher degree of correlation of the two DIBs
with the extinction. We demonstrate that it is simply due to the lower
temperature and intrinsic luminosity of our targets. Using cooler target stars
reduces the number of outliers, especially for nearby stars, confirming that
the radiation field of UV bright stars has a significant influence on the DIB
strength. We have used the cleanest data to compute updated DIB shapes.
