We have carried out photometric follow-up observations of bright transiting extrasolar planets using the CbNUOJ 0.6 m telescope. We have tested the possibility of obtaining high photometric precision by applying the telescope defocus technique, allowing the use of several hundred seconds in exposure time for a single measurement. We demonstrate that this technique is capable of obtaining a root-mean-square scatter of sub-millimagnitude order over several hours for a V ~10 host star, typical for transiting planets detected from ground-based survey facilities. We compared our results with transit observations from a telescope operated in in-focus mode. High photometric precision was obtained due to the collection of a larger amount of photons, resulting in a higher signal compared to other random and systematic noise sources. Accurate telescope tracking is likely to further contribute to lowering systematic noise by exposing the same pixels on the CCD. Furthermore, a longer exposure time helps reduce the effect of scintillation noise which otherwise has a significant effect for small-aperture telescopes operated in in-focus mode. Finally we present the results of modelling four light-curves in which a root-mean-square scatter of 0.70 to 2.3 milli-magnitudes was achieved.

1. INTRODUCTION
 2. DEFOCUS PHOTOMETRY
 3. OBSERVATIONS
 4. DATA REDUCTION
 5. LIGHT-CURVE MODELLING
 6. RESULTS – 1
 7. RESULTS – 2
  7.1 Treatment of limb-darkening
  7.2 Treatment of parameter uncertainties
 8. CONCLUSION
 ACKNOWLEDGEMENTS
 REFERENCES

• Chun-Hwey Kim(Chungbuk National University Observatory, Cheongju 361-763, Korea, Chungbuk National University, Cheongju 361-763, Korea)
• Yong-Gi Kim(Chungbuk National University Observatory, Cheongju 361-763, Korea, Chungbuk National University, Cheongju 361-763, Korea)
• Chung-Uk Lee(Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea, Korea University of Science and Technology, Yuseoung Gu, Daejeon, 305-350, Korea)
• Joh-Na Yoon(Chungbuk National University Observatory, Cheongju 361-763, Korea)
• Wonyong Han(Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea, Korea University of Science and Technology, Yuseoung Gu, Daejeon, 305-350, Korea) Corresponding author
• Tobias C. Hinse(Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea, Armagh Observatory, College Hill, BT61 9DG Armagh, United Kingdom)