The theoretical angular resolution limit one can reach when using speckle
techniques depends upon 
, where 
is the wavelength used
and D is the telescope diameter. Thus, large instruments such as the
3.6-m ESO or CFH telescopes have a higher potential than the TBL, although
and 
, respectively the coherence radius and coherence time of
the atmospheric seeing at Pic du Midi get exceptionally large values
for about one month per year. As solar observations have demonstrated,
the Pic du Midi site features slow seeing and extended
isoplanetic patch, which indicates that the TBL is potentially well suited
to speckle and adaptive optics observations, despite its modest size. With
a diffraction limit at 0.06" in V, the TBL can provide high
quality data from which many astrophysical programs could benefit.
Nevertheless, we have not been lucky yet with the weather conditions at
Pic du Midi. Another problem arises as the whole site is currently rebuilt
and temporarily closed to public and astronomers.
Due to the necessary short exposure times and narrow spectral bandpass, photon noise is the most severe limiting factor in speckle imaging (Dainty and Greenaway, 1979, Beletic and Goody, 1992). The limiting magnitude depends on the atmospheric seeing, the spectral bandpass, the angular resolution to be achieved, and the quantum efficiency of the detector. (Dainty and Greenaway, 1979). We should reach V=12-14 with the TBL and detectors such as the CP40 and the PAPA. Up to now the faintest objects we have observed had a V magnitude of 11.