Purchase A Research Grade Telescope
What makes a telescope "Research grade?  Answere: The quality of its optics and instrumentation.  Every amateur Astronomer knows about the importance of quality optics, but the vast majority of commercially available telescopes fail to meet Baron Rayleigh's famous definition a telescope. Advertisers often claim a failed telescope has "Diffraction Limited Optics" implying it is a fine telescope, - while all along it is not "Diffraction Limited" as a whole instrument, and therefore does not qualify as a telescope at all. There are so many high priced, failed telescopes on the market boasting of fine quality optics that it has become necessary to advertise telescopes that do meet Baron Raleigh's criterion as "research grade" telescopes.
However, researchers are not as gullible as the general population, and expect more than just a minimal telescope for research purposes. The images of a research grade telescope must be distortion free for making accurate measurements. A telescope Main Mirror that just has a Peak-to-Valley Wavefront of Error of 1/8 at 550 nm on the test bench, used with a Secondary mirror that also has a Peak-to-Valley Wavefront Error of 1/8 at 550 nm on the test bench, - should combine to produce a telescope with a Peak-to-Valley Wavefront Error of 1/4 at 550 nm. This telescope just meets Baron Rayleigh's definition of a telescope.
Unfortunately that is not the whole story. If the thickness of the Main Mirror is less than 20% of its diameter, the mirror will sag, requiring extra support to prevent this sagging. The complex pattern of the required mirror supports introduces stresses on the mirror resulting in a complex pattern of distortions across the mirror's surface. The mirror has just lost its diffraction limited rating in a most non-uniform fashion making the telescope fail Baron Rayleigh's definition of a telescope.