Deep narrow band interference filters observations are presented for 7 type I galactic planetary nebulae (PNe). Except for the nearly circular planetary nebula A 39, the observations show overall dimensions appreciably larger than those quoted so far. The observed PN (NGC 6302 excepted) could have linear diameters larger than 1pc. Our new observations imply ionized masses often larger than 1 M☉, suggesting that much of the mass ejected by the PN precursor is contained in faint outer extensions. This might contribute to the solution of the ``mass deficit" in PNe. We have also provided calibrated fluxes for some specific emission lines. In spite of their apparent morphological differences, our observations suggest that these type I PNe possess the same intrinsic structure as that displayed by NGC 650-1, the Ring Nebula, and even Sh 1-89 with its elongated jet-like feature, but viewed under different angles.