FTN z-band and Euler r-band follow-up high signal-to-noise photometry of WASP-39b during the transit. The Euler light curve has been ofsetted from zero by an arbitrary amount for clarity. The data are phase-folded on the ephemeris from Table 4. Superposed (black-solid line) is the best-fit transit model estimated using the formalism from Mandel & Agol (2002). Residuals from the fit are displayed underneath.