>>13845188Sure.
>It is especially "the pair" that confuses me. The diagram in >>13842444 shows several telescopes made up of two main mirrors, so why would this not work here?It could work, but it's not well suited for interferometer. Note that not all of the telescopes which have two mirrors can actually combine them as an interferometer. Only the ones connected by a dashed circle. The Keck interferometer was shut down many years ago (because a project to build outriggers was blocked).
In an interferometer you combine the light from different telescopes in pairs and measure interference fringes. A pair is called a baseline. The resolution of this measurement is related to the separating of the telescopes (the length of the baseline). Measuring the signal from each baseline only gives you some information about the image, to make a nice image you want lots of baselines with different lengths and angles. If you have only two telescopes you have just one pair. If you have three telescopes, you have three unique pairs. Four telescopes gives you 6 unique baselines. This is why radio interferometers like the VLA and ALMA have lots of antennas.
Most optical/visible interferometers use similar telescopes. If you have one very big telescope and a bunch of smaller ones you have problem. The measured fringes of the baselines which include the ELT would have lots of light, so a strong signal. But the fringes for the baselines which just have two small telescopes (most of the pairs) will be much noiser. And so these noisy measurements won't contain much information. You don't do as well because many of your measurements are crap. They just won't add much information.
