The [O II]3726,3729Å doublet is sensitive to electron densities in the range 100 to 104 cm–3, typical of planetary nebulae, and thus provides an ideal tool for mapping the projected density structure. The first use of the imaging Fabry-Perot TAURUS-II to observe both the [O II] doublet lines, and hence map the electron density, is reported for NGC 6826. If sufficient spectral resolution is achieved both the [O II] lines can be resolved into separate components, opening the way to full 3-D density mapping of PN. Given the low finesse of the etalon and the low expansion velocity in NGC 6826 (10-15 kms–1), this original hope could not be fulfilled. However, a restricted aim of seeing-limited electron density mapping was accepted.