Context : Dust plays a significant role in planetary nebulae .
Dust ejected with the gas in the asymptotic giant branch ( AGB ) phase is subject to the harsh environment of the planetary nebula ( PN ) while the star is evolving towards a white dwarf .
Dust surviving the PN phase contributes to the dust content of the interstellar medium .

Aims : The morphology of the internal dust extinction has been mapped for the first time in a PN , the bright nearby Galactic nebula NGC 7009 .
The morphologies of the gas , dust extinction and dust-to-gas ratio are compared to the structural features of the nebula .

Methods : Emission line maps in H Balmer and Paschen lines were formed from analysis of MUSE cubes of NGC 7009 observed during science verification of the instrument .
The measured electron temperature and density from the same cube were employed to predict the theoretical H line ratios and derive the extinction distribution across the nebula .
After correction for the interstellar extinction to NGC 7009 , the internal A _ { V } / N _ { H } has been mapped for the first time in a PN .

Results : The extinction map of NGC 7009 has considerable structure , broadly corresponding to the morphological features of the nebula .
The dust-to-gas ratio , A _ { V } / N _ { H } , increases from 0.7 times the interstellar value to > 5 times from the centre towards the periphery of the ionized nebula .
The integrated A _ { V } / N _ { H } is about 2 \times the mean ISM value .
A large-scale feature in the extinction map is a wave , consisting of a crest and trough , at the rim of the inner shell .
The nature of this feature is investigated and instrumental and physical causes considered ; no convincing mechanisms were identified to produce this feature , other than AGB mass loss variations .

Conclusions : Extinction mapping from H emission line imaging of PNe with MUSE provides a powerful tool for revealing the properties of internal dust and the dust-to-gas ratio .