  We have studied the Residual Blaze Functions (RBF) resulting from division of
individual echelle orders by extracted flat-field in spectra obtained by
slit-fed OES spectrograph of 2m telescope of Ond\v{r}ejov observatory, Czech
Republic. We have eliminated the dependence on target and observation
conditions by semiautomatic fitting of global response function, thus getting
the instrument-only dependent part, which may be easily incorporated into data
reduction pipeline. The improvement of reliability of estimation of continuum
on spectra of targets with wide and shallow lines is noticeable and the merging
of all orders into the one long spectrum gives much more reliable results.

Instrumentation and Methods for Astrophysics