First proposed by Grottesman et al [Phys. Rev. Lett. 109, 070503 (2012)], the quantum telescopic technique is to use spatially entangled single-photon states as references to modify the traditional Hanbury Brown-Twiss (HBT) intensity stellar interferometric technique. The technique can rival the Michelson stellar interferometry in signal level but is not restricted by the baseline size, so it has the potential to significantly increase the resolution in astronomical imaging in the optical domain. In practice, single-photon states generated in the lab are usually not ideal in that they have finite bandwidth and non-unit efficiency. Furthermore, detectors also have finite response time and celestial light has a bandwidth. All of this will have an impact on the effectiveness of the quantum telescopic technique. In this work, we consider a spatially entangled singe-photon state generated by beam-splitting a practical anti-bunched photon source from resonance fluorescence, which is a common method of generating single-photon states, and evaluate the signal level in quantum telescopy with inclusion of imperfection of detection system and finite bandwidth of celestial light. Here, given the incoming light, we optimize the parameters of the anti-bunched photon source and the detector system for the best signal-to-noise ratio (SNR), which can match that of the Michelson method in the ideal case but is always smaller in the realistic case. Alternatively, weak coherent states from heavily attenuated lasers can replace the entangled single-photon state but suffer low signal level, similar to HBT method. We find that the SNR with a realistic anti-bunched source can still beat the SNR of the coherent state scheme in the weak incoming field limit. The optimized parameters for the anti-bunched sources and detection system will be a guide for future experimental endeavor.