At what size aperture of a telescope become useless and doesn't change at all from the previous aperture?
What I mean is if you go up from a 1 inch aperture to a 6 inch aperture, you are going to see A LOT more than you would from the 1 inch. But an 8 meter aperture to a 10 meter aperture doesn't change much at all, at what aperture does nothing change if you make it larger?
What I mean is if you go up from a 1 inch aperture to a 6 inch aperture, you are going to see A LOT more than you would from the 1 inch. But an 8 meter aperture to a 10 meter aperture doesn't change much at all, at what aperture does nothing change if you make it larger?
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There are mnay, many aspects to this question.
To start at the beginning, resolution varies with the diameter of the objective, so in those terms, moving from 8m to 10m isn't going to make all the difference in the world. On the other hand, light grasp varies as the square of diameter, so the light grasp of a 10m will be almost exactly 50% better than that of an 8m. So, all other things being equal, you could cut exposure times for a given photograph by a third b moving up to 10m.
That's the theory. Practice can be different. For example, there will be circumstances (bad seeing) where the view from binoculars (say 2") will be better than that through a 6" telescope. The binocular image may dance about a bit, but that in the telescope will just be blurred. The reason is that 6" is taking samples of light paths through too many different atmospheric conditions.
Also, there is the question of weight. A 10m telescope may weigh far more than an 8m, so that on a like for like basis, it would give a much worse image because of the engineering issues of supporting a) the mirror cell and b) the entire telescope. In other words, the whole telescope and mount have to be engineered to a far higher standard for a 10m if it is to perform to the same standard as an 8m. These are the sorts of problems which have limited telescope sizes in the past.
However, given modern top-class engineering, with segmented mirrors, adaptive optics, modern materials and so on, there is no real limit to the productive size of a telescope. As with so many other areas of astronomy, the limiting factor is simply the cost - or more accurately, the willingness of voters who have no interest in or knowledge of astronomy to bear the cost. You don't find privately-funded cutting-edge telescopes these days.
To start at the beginning, resolution varies with the diameter of the objective, so in those terms, moving from 8m to 10m isn't going to make all the difference in the world. On the other hand, light grasp varies as the square of diameter, so the light grasp of a 10m will be almost exactly 50% better than that of an 8m. So, all other things being equal, you could cut exposure times for a given photograph by a third b moving up to 10m.
That's the theory. Practice can be different. For example, there will be circumstances (bad seeing) where the view from binoculars (say 2") will be better than that through a 6" telescope. The binocular image may dance about a bit, but that in the telescope will just be blurred. The reason is that 6" is taking samples of light paths through too many different atmospheric conditions.
Also, there is the question of weight. A 10m telescope may weigh far more than an 8m, so that on a like for like basis, it would give a much worse image because of the engineering issues of supporting a) the mirror cell and b) the entire telescope. In other words, the whole telescope and mount have to be engineered to a far higher standard for a 10m if it is to perform to the same standard as an 8m. These are the sorts of problems which have limited telescope sizes in the past.
However, given modern top-class engineering, with segmented mirrors, adaptive optics, modern materials and so on, there is no real limit to the productive size of a telescope. As with so many other areas of astronomy, the limiting factor is simply the cost - or more accurately, the willingness of voters who have no interest in or knowledge of astronomy to bear the cost. You don't find privately-funded cutting-edge telescopes these days.