Hard X-ray telescopes using depth-graded multilayer is a key technology for future satellite programs. Developments are underway by many groups, and balloon experiments have also been carried out. We have developed light-weight hard X-ray telescopes using Pt/C multilayer and high-throughput thin-foil optics. They have been aboard on InFOCμS and SUMIT balloon flights. As a next development efforts, especially for Japan's NeXT satellite program, we focus on improvement of image quality. Among three equally-contributing error factors (figure error, positioning error and off-roundness), figure errors and off-roundness have been reduced significantly, by screening of replication mandrels and active and iterative tuning of support bars. Further studies are in progress, such as suer-polished metal mandrels and better positioning of reflector edges, to meet the baseline requirement of the NeXT mission.