Ok, well I see nobody came up with this, and I've thought about it more. The whole point of putting up a huge ring instead of a huge lens, is again, to save weight. But with astronomy it is usually not the triangulation accuracy that matters, as in, 3d-vision of knowing the distance, but light collection and image sharpness. So what I said about partial outer fresnel lens rings, binocular style, is not correct, the very purpose of the ring is increased light collection surface area all focusing to a single point to create the image, doing it at minimum weight possible, and if they carried on along the lens, it would get prohibitively heavy in the center. However, this problem of increased surface area without increasing the weight has been already solved, and it's called the Fresnel lens itself. And in fact, the central rings of the Fresnel are the lightest, because they can be made flat and nearly parallel, so super thin, while the outermost rings are the heaviest, because of the steep angle requirements for diffraction there, unless you are willing to increase the frequency of the rings making them each skinnier and narrower, compared to pretty fat stripes of glass in the center. Also the achromatic requirement for the materials near the outer rings increases - meaning the prism-like refracting glass cannot split the colors of the rainbow, but the material has to be accurately achromatic for all frequencies, possibly UV and infrared too, or whatever you can get. So as far as astronomy goes, and light collection surface area just an opaque disk in the center is no better than a traditional Fresnel lens, other than the requirement on the accuracy of shape and accuracy of focal point manufacturing, which may be slightly less of a problem with a single outer ring, but why not pay attention and tune it to the max you can tune it, instead of putting up an opaque disk. Even with an opaque disk the opaque part needs to be closer to the lens, so that when you have to steer the gigantic ring contraption with rocket fuel, you only have to move the ring, not the opaque disk which is close to the camera or focal point, and if you go with a Fresnel lens, you could have locally installable and removable filters that could block out certain rings at a time if needed, and only allow the outermost one, or innermost-ones to collect the light, or if you allowed slight achromaticity, varying the focal point could collect the blue, red, yellow, etc portions along the rainbow individually, including UV and infrared by themselves too, which then you can computer compound to reconstruct the image.
So in the astronomy sense of looking at distant galaxies, the binocular 3D vision sense, kind of like looking out into the sea for ships from a port, and seeing the distance with binoculars which is not possible with a single telescope, so for astronomy sense the 3D effect is not important, because the base of the triangle you use in your computations to get your 3D view is so minuscule compared to the hypotenuse and other sides of the triangle, that the math still spits out error, and you cannot tell how far a galaxy is with a couple hundred mile binocular spacing, maybe a spacing that spans the entire solar system between two telescope looking at the exact same thing might work. However what a 3D vision can do in space is see nearby objects, or search for nearby objects. You simply put your eyeballs into a cross-eye for near range, such as looking between Neptune and Pluto, or just behind Pluto, and then whatever you're looking at, if any objects come into intense focus while everthing before them and behind them blurs out, you can instantly find meteorites, even if they are extremely small, headed for Earth. We just had a near miss of a fairly gigantic meteorite that whizzed by Earth and missed, on Jan 26, and the non omnipotent lifeforms on Earth that split the Red Sea during Exodus could have altered its course to make it slam into Earth, precipitating a global catastrophe that would instantly put an end to stupid lawn mowing that people do everywhere, simply because oil shipments would have stopped, and then using manual scythes is actually not a problem for bugs, flowers, mushrooms and other lifeforms, on grass and flowers that have grown knee high, but the constant harassment every 2 days by a lawnmower and complete lack of flowers, that is a problem presently that needs to be addressed. So there is more time until another one of these near misses whizzes by and intentionally gets crashed to put an end to the out of control often senseless natural destructive behavior of one of the species on Earth, called humans. And in that cutting grass to create a couple foot protective zone from snake in the grass for your kids around the house is not a problem, if you want to. Or if you have to destroy weeds because you need to grow food there. Or you have to hunt to feed yourself, but not for mass market. Or you have to pollute a natural water in a way where it can easily absorb it and deal with the pollution without extinction issues, but you make a living on it, in economically dire circumstances. Like my cat Geoffrey only destroys when he's hungry, and even then 1 out of 7 mice escape by his dabblings. It's the out of control senseless and useless destruction, such as grass cutting on an uninhabited lot, or even, say Walmart street front lots, over mere sense of beauty is what's at stake here, and if you do not like the flowers and weeds that have been around for hundreds of millions of years, you can import other flowers that are prettier to you and more pleasing to your eyes, but there is a desperate need for flowers, for butterflies, bees and even ants, and in turn spiders, dragonflies to live happily. So in any case, having binocular like searching telescopes sweeping in plane and out of plane of the planets (the recent near miss whizzz by was coming way out of plane) 3d-vision looking for anything that turns up in-focus is a worthy thing to do, and for that you need a decent size triangle base for the trigonometric sine cosine triangulation land surveyor calculations, which your brain processes unknowing to you when you see in 3D vision one object farther than another.
By the way the chromaticity issues arising with lenses and prisms have also been solved already, including in astronomy, through eliminating diffraction and instead using total reflection, i.e. paraboloid mirrors, like in your flashlight, but instead of a light bulb at the focal point giving you a parallel beam, you put a concave paraboloid mirror at the bottom of a pipe, and put the camera where he light bulb would be to collect the image. So while even for a Fresnel lens you need some kind of thickness except for the very flat central part, for mirrors you can make those any small thickness that is structurally still sound, and even break them up into individually movable portions (and then you have to get very good with the alignment technology, such as laser interferometry distance measurements between 2 or 3 mirrors to pick up their precomputed positions when trying to aim at something.) But here, if you truly want to save on weight for a telescope instead of using a single Fresnel lens ring around the outer edges and blacking out the center ones with an opaque material, make that opaque material into a paraboloid mirror (possibly from Moon-mined aluminum), and in space where the only bother is solar wind plus micro-meteorites, possibly aluminum foil thickness might be acceptable, as long as you can create an accurate shape. Either with the Fresnel lens ring, or multi ringed huge Fresnel lens, or the mega-paraboloid mirror, the issue is geometrical accuracy in the mirror shape. On Earth they used to use mercury-pools set aspin, and the spinning created a super-accurate paraboloid surface on mercury, kind of like when you spin a bucket of water the water surface rises up at the sides, and the center stays flat but depressed, a parabolid shape, of course not accurate in practice if you just jerked the bucket, but should be pretty accurate if you have maintained uniform spinning for a while. Of course in weightlessness there is no driving force to force a liquid surface into a paraboloid, so for artificial gravity you may need a big rotating cylinder space station where you produce individual paraboloid elements of the paraboloid mega mirror to check your CNC calibrations, unless you trust your CNC's enough to accurately make the individually tiltable laser interferometry alinged paraboloid components, that line up on command to focus light from a distant galaxy, and get out of focus when a bright object passes by in the view, such as a planet, to not burn up the camera by heating it to the boiling point of tungsten, desert solar concentrator style, merely off of the light they collect reflected from, say, Uranus.