Comment Like HST (but not in a good way) (Score 1) 101
It's an impressive amateur engineering feat, but its performance as a telescope might not be anything to write home about. It probably shares one quality with the hubble that you wouldn't want: a problem with gravity.
Remember how when it first went up, the hubble had problems focusing clearly? The designers forgot that its mirrors would be deformed/reshaped by the lack of gravity. Essentially, the hubble's primary mirror was optically designed to work as a telescope mirror on earth, not in space. It wasn't until the later mission to fix it with some corrective optics that it really achieved its best capabilities.
Now, since the surplus 70" mirror this guy used was designed to work on a satellite, it would very likely have the same problem but in reverse. If the mirror was designed to be shaped properly in a microgravity environment, it would also be deformed when on earth (as it is when used in the amateur telescope.) That might make the images from it quite a bit worse than one might hope for from a 70" instrument.
Remember how when it first went up, the hubble had problems focusing clearly? The designers forgot that its mirrors would be deformed/reshaped by the lack of gravity. Essentially, the hubble's primary mirror was optically designed to work as a telescope mirror on earth, not in space. It wasn't until the later mission to fix it with some corrective optics that it really achieved its best capabilities.
Now, since the surplus 70" mirror this guy used was designed to work on a satellite, it would very likely have the same problem but in reverse. If the mirror was designed to be shaped properly in a microgravity environment, it would also be deformed when on earth (as it is when used in the amateur telescope.) That might make the images from it quite a bit worse than one might hope for from a 70" instrument.