The precursor of the current 39.3 m diameter ELT was the 42 m E-ELT of ESO, currently being built on the Cerro Armazones in Chile. When it was announced several years ago that the downscaling had been decided due to budgetary reasons a study of the observing potential of the new 39.3 m telescope claimed there would be no major losses. But I am wondering what exactly won't be possible with the 2.7 m aperture decrease. If it doesn't hurt much in observing potential why not design the E-ELT as 39.3 m in the first place? What apart from longer exposure times for a specific desired SNR won't be possible to achieve with the downscaled telescope? Does anyone now more?
Downscaling of the E-ELT
Posted 28 September 2019 - 06:45 PM
It's hard to answer that question in detail, because the scopes are designed with specific instrument capabilities in mind, by the time they're complete the technology of imaging instruments has moved on and the capabilities are not exactly what was originally designed for. So, maybe they are just referring to cost/benefit ratio, or maybe there are new imagers that can do at the smaller size what the original larger scope had envisoned.