We have developed a setup that fully reproduces the TNT output beam in term of geometrical parameters (beam aperture, central obscuration, PSF size) and wavefront quality. This setup provides an equivalent angular resolution at the TNT level better than 0.2’’ and will be used to test the instrument currently in development for the TNT: a focal reducer [4] and a long-slit spectrograph. The next steps will aim at improving the system spatial resolution and at characterizing the stability of the system. In a first time, we will improve the setup image quality by finely adjusting the position of the telescope primary mirrors to remove the residual spherical aberration. In a second time, we will characterize the long term variations of the WFE at the setup to identify the potential optimization. The ultimate goal of
these optimizations is to provide stable diffraction-limited images to test high-resolution imaging instruments.