1 Introduction

Planetary nebulae (PNe) are defined by their emission-line spectrum and often show extended nebulosities with definite morphological structures. However, PNe with large angular sizes are relatively rare. Among the $\approx$ 2000 PNe catalogued (Perek & Kohoutek 1967; Acker et al. 1992, etc.), less than 1% are larger than 10'. Large, extended PNe are often characterized by very faint brightness. They were first discovered and systematically studied by Abell (1966) using the Palomar Observatory Sky Survey plates. This pioneering work was later extended by Weinberger et al. (1983) who discovered more larger and fainter PNe. The extreme low surface brightness of these extended PNe has been attributed to the result of expansion. The Abell PNe are believed to be old and their central stars presumably have evolved past the constant-luminosity phase and are now on the cooling tracks. Because of their faintness, these PNe are likely to be discovered only if they are nearby, within the distances of 200-1000 pc (Ishida & Weinberger 1987).

Large surrounding haloes have also been detected in some of the Abell objects (e.g. A 65, A 66, Hua et al. 1998, and also via ftp://www.astrsp-mrs.fr/axes-scientifiques/nebuleuses-planetaires). Recent development of large-format CCD detectors has made possible to imaging of these PNe with large field of view and high dynamical range. In this paper, we report new data consisting in narrow-band images of 7 Abell PNe and discuss possible relations between their morphologies and state of evolution.