When measuring high-quality diffraction **data** for HPMX experiments, care should be provided in selecting the optimum wavelength. The chosen energy will have a direct influence on the resolution, signal-to-noise ratio, X-ray absorption by cell components, and will be dependent on the detector characteristics, often optimized for a specific set of energies. Ultra-short wavelengths of the order of 0.25-0.05 Å have been reported as being optimal for HPMX studies (Fourme et al., 2001). At AR-NW12A, the shortest wavelength available is 0.70 Å , limited by the cut-off ($ 3.5 mrad) of the focusing mirror reflectivity downstream of the monochromator, rather than by the X-ray undulator source (see Fig. 1 of Chavas et al., 2013). A typical diffraction pattern recorded during HPMX experiments is shown Fig. 3. Although sub-optimal, **data** collection at 0.70 Å should increase the crystal lifetime approximately by a factor of two, when compared with **data** collection at 1.00 Å , in accordance with calculations of the dose-dependent decay of crystals exposed to wavelengths of 0.70 Å and 1.00 Å , respectively, with a conserved incoming flux of 1.0 Â 10 11 photons s À1 mm À2 in an area of 200 mm Â 200 mm (calculations performed using Raddose version 2.0; Paithankar et al., 2009). Moreover, the ADSC Quantum 210r CCD X-ray detector implemented at AR-NW12A is calibrated to have its detective quantum efficiency (DQE) maximized at the wavelength of 1 Å . Although no major troubles could be observed in the **data** recorded so far with an energy beam of 17.7 keV (0.70 Å ), HPMX at AR-NW12A could improve in **data** quality if a detector calibrated for higher energies was available. The recommended beam size at AR-NW12A varies from 100 mm Â 100 mm to 200 mm Â 200 mm, in positive cases where access to sufficiently large crystals is possible. A clear advantage of this large beam size lies in the fact that a larger volume of the crystal is exposed to the X-ray beam, resulting in increased signal at higher energies. A comparison of **data** collected at PF AR-NW12A with **data** recorded at SPring-8 BL41XU (Kawamoto et al., 2001), where a sharper beam was available, clearly suggested that a larger beam size coupled with a lower flux was beneficial for collecting fully usable **data** at room temperature (unpublished results).