research papers 1208 https://doi.org/10.1107/S1600577519005708 J. Synchrotron Rad. (2019). 26, 1208–1212 Received 4 April 2019 Accepted 25 April 2019 Edited by P. A. Pianetta, SLAC National Accelerator Laboratory, USA Keywords: compound refractive lenses; X-ray microscopy; synchrotron radiation. Supporting information: this article has supporting information at journals.iucr.org/s CRL-based ultra-compact transfocator for X-ray focusing and microscopy Anton Narikovich, a Maxim Polikarpov, b Alexander Barannikov, a Nataliya Klimova, a Anatoly Lushnikov, a Ivan Lyatun, a Gleb Bourenkov, b Dmitrii Zverev, a Igor Panormov, a Alexander Sinitsyn, a Irina Snigireva c and Anatoly Snigirev a * a Immauel Kant Baltic Federal University, Nevskogo 14, 236041 Kaliningrad, Russian Federation, b European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 25a, 22607 Hamburg, Germany, and c European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France. *Correspondence e-mail: asnigirev@kantiana.ru A new ultra-compact transfocator (UCTF) based on X-ray compound refractive lenses (CRLs) is presented. The device can be used to change the number of one- and two-dimensional focusing CRLs by moving the individual parabolic lenses one-by-one independently, thus providing permanent energy and focal- length tunability for scanning and full-field X-ray microscopy applications. The small overall size and light weight of the device allow it to be integrated in any synchrotron beamline, while even simplifying the experimental layout. The UCTF was tested at the Excillium MetalJet microfocus X-ray source and at the P14 EMBL (PETRA-III) beamline, demonstrating high mechanical stability and lens positioning repeatability. 1. Introduction Since the first successful implementation of X-ray compound refractive lenses (CRLs) (Snigirev et al. , 1996), they have become standard elements at many synchrotron beamlines (Dimper et al., 2014). Modifying shape, composition and number of individual lenses, CRLs can be adapted to photon energies from 2 keV to 200 keV, providing flexible adjustment of focal lengths and versatility for a wide range of applications (Snigirev & Snigireva, 2008). CRLs can provide beam condi- tioning functions, i.e. condensers (Polikarpov, Snigireva and Snigirev, 2016), collimators (Baron et al., 1999; Chumakov et al., 2000), beam-shapers (Zverev et al. , 2017) and higher- harmonic suppressors (Polikarpov et al. , 2014). Currently, CRLs are extensively used in X-ray imaging and microscopy (Byelov et al. , 2013; Zverev et al. , 2017, 2018), interferometry (Snigirev, Snigireva, Kohn et al., 2009; Snigirev et al. , 2014; Zverev et al. , 2018) and spectroscopy (Santoro et al. , 2014). Use of refractive optics allows us to track dynamical and structural transformations, which is especially important in studies of materials under extreme conditions (Dubrovinskaia et al., 2016) and in high-resolution X-ray diffraction experi- ments (Drakopoulos et al. , 2005; Ershov et al. , 2015). In a typical X-ray experiment, a considerable number of individual lenses have to be coaxially grouped to focus radiation at a certain distance and given energy. A system with arrays of planar refractive lenses aligned in parallel was designed to combine the advantages of compound refractive optics with the precise alignment possibilities of planar micro- fabrication technologies (Snigirev et al. , 2002, 2007; Poli- karpov, Polikarpov et al. , 2016). To align two-dimensional lenses in experiments with tunable energies, however, a system ISSN 1600-5775 # 2019 International Union of Crystallography