Context :

Aims : We analyse the photometric properties of the early-type Fornax cluster dwarf galaxy population ( M _ { V } > -17 mag ) , based on a wide field imaging study of the central cluster area in V and I bandpasses .
We used the instrument/telescope combination IMACS/Magellan at Las Campanas Observatory , providing much larger light collecting area and better image resolution than previous wide field imaging surveys .

Methods : We create a fiducial sample of Fornax cluster dwarf ellipticals ( dEs ) in the following three steps : ( 1 ) To verify cluster membership , we measured I -band surface brightness fluctuations ( SBF ) distances to candidate dEs known from previous surveys ; ( 2 ) We re-assessed morphological classifications for those candidate dEs that are too faint for SBF detection ; and ( 3 ) We searched for new candidate dEs in the size-luminosity regime close to the resolution limit of previous surveys .

Results : ( 1 ) We confirm cluster membership for 28 candidate dEs in the range -16.6 < M _ { V } < -10.1 mag by means of SBF measurement .
We find no SBF background galaxy .
( 2 ) Of 51 further candidate dEs in the range -13.2 < M _ { V } < -8.6 mag , 2/3 are confirmed as probable cluster members by morphological re-assessment , while 1/3 are re-classified as probable background objects .
( 3 ) We find 12 new dE candidates in the range -12.3 < M _ { V } < -8.8 mag , two of which are directly confirmed via SBF measurement .
The resulting fiducial dE sample follows a well-defined surface brightness - magnitude relation , showing that Fornax dEs are about 40 % larger than Local Group dEs .
The sample also defines a colour-magnitude relation that appears slightly shallower than that of Local Group dEs .
The early-type dwarf galaxy luminosity function in Fornax has a very flat faint end slope \alpha \simeq - 1.1 \pm 0.1 .
We discuss these findings in the context of structure formation theories .

Conclusions : The SBF method is a very powerful tool to help constrain the faint end of the galaxy luminosity function in nearby galaxy clusters .
For the Fornax cluster , morphological cluster memberships – if performed at sufficient resolution – are very reliable .