Left: the real part of the visibility as a function of baseline for observations of A1689 using the CBI1 (grey error bars) and CBI2 (black error bars). The short error bars represent the 1σ noise from the variance in the data, and the long error bars represent the total statistical uncertainty including the intrinsic CMB anisotropy. There is about 50 per cent more usable data in the CBI1 observations than in the CBI2 observations. Middle and right: cleaned full-resolution maps of A1689 using the CBI1 and CBI2 arrays, respectively. The rms noises on each map are 5.9 mJy beam⁻¹ for CBI1 and 6.1 mJy beam⁻¹ for CBI2. The contours are multiples of 6 mJy beam⁻¹. The FWHM of the synthesized beam is shown in the bottom left-hand corner of each map (8.6 × 8.7 arcmin for CBI1 and 5.3 × 6.0 arcmin for CBI2). The FWHM of the primary beam, at ν = 31 GHz, is shown as a dark circle centred on each map (45.1 arcmin for CBI1 and 28.2 arcmin for CBI2).