Challenges for Doing Quantitative Astronomy with ELTs
Extremely large telescopes will push the limits of astronomical observations to a level not achievable with the current generation of telescopes. It will be possible to observe to fainter magnitude limits and, with adaptive optics, with higher angular resolution due to the sizes of the primary mirrors. In addition it is expected that "quantitative techniques" such as astrometry and photometry will achieve levels of accuracy not possible today. This requires controlling the error sources affecting such measurements, for example distortions caused by all parts of the optics, to a higher level of accuracy for much larger components than on current telescopes. It might also be necessary to adapt calibration procedures and observing techniques in some cases. In this talk I will give an overview over the challenges this presents for the design, construction and operation of ELTs, concentrating on the example of precision astrometry.