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Before I read this... "focal region" sounds nonsensical to me. Surely the focal length and direction depends on the thing you want to look at? The "focal region

Before I read this... "focal region" sounds nonsensical to me. Surely the focal length and direction depends on the thing you want to look at? The "focal region" would be something like a sphere starting some distance from the sun and extending out in all directions to infinity?

WithinReason 4y ago
I think that's why it's called a focal region instead of a focal point.
Orothrim 4y ago
I don't believe so, I believe that the size and gravity of the sun have a gravitational effect on space an result in a focusing of light at 500+AU distance from the sun. Hence the focal region is around this sphere and is where you would "sit" to use the sun as a lens and get information about the universe on the opposite side of the sun. https://en.wikipedia.org/wiki/Solar_gravitational_lens https://en.wikipedia.org/wiki/Solar_gravitational_lens
simias 4y ago
Given the scales we're talking about I presume that everything you want to look at is effectively "at infinity", as such I expect that you consider where two parallel rays would meet due to solar lensing and that's your focal region.
krisoft 4y ago
> Surely the focal length and direction depends on the thing you want to look at? Yes. And "aiming" your observatory involves moving it on that sphere. Given the distances involved that is pretty much either impossible or time prohibitive. The region starts at 548 AU from the Sun. So 548 times the average Sun-Earth distance. In an ideal world you would teleport your camera to this location instantaneously, take a picture and then teleport to the next location to look at something else. We don't know how to do that. The distances are immense. So instead we pick a target, and send out a satellite or satellites on the opposite vector from it to take a peek. There is a single point where the target will be in perfect focus, but in practice (as the paper shows) the target is "in-focus" enough in a larger region that your satellites can take a picture while they fly through the region around the ideal point.
- ur-whale 4y ago
  If all this effort is expended only to look at a single object, the whole idea seems kind of pointless. However, we are using the mental model of a camera lens to reach that conclusion, and I'm not certain it applies: 1) even if we use the mental model of a camera lens, given the distances involved, you can probably consider most of the interesting the targets to be "at infinity" 2) I'm not certain that a gravitational lens works like a camera lens.
  - samus 4y ago
    It behaves differently of course, and the pictures would be massively distorted. But with some image processing it should be possible to do some analysis. One of the recent JWST images shows an example where a massive galaxy cluster makes redshifted galaxies behind visible.

WithinReason 4y ago

I think that's why it's called a focal region instead of a focal point.

Orothrim 4y ago

I don't believe so, I believe that the size and gravity of the sun have a gravitational effect on space an result in a focusing of light at 500+AU distance from the sun. Hence the focal region is around this sphere and is where you would "sit" to use the sun as a lens and get information about the universe on the opposite side of the sun. https://en.wikipedia.org/wiki/Solar_gravitational_lens https://en.wikipedia.org/wiki/Solar_gravitational_lens

simias 4y ago

Given the scales we're talking about I presume that everything you want to look at is effectively "at infinity", as such I expect that you consider where two parallel rays would meet due to solar lensing and that's your focal region.

krisoft 4y ago

> Surely the focal length and direction depends on the thing you want to look at? Yes. And "aiming" your observatory involves moving it on that sphere. Given the distances involved that is pretty much either impossible or time prohibitive. The region starts at 548 AU from the Sun. So 548 times the average Sun-Earth distance. In an ideal world you would teleport your camera to this location instantaneously, take a picture and then teleport to the next location to look at something else. We don't know how to do that. The distances are immense. So instead we pick a target, and send out a satellite or satellites on the opposite vector from it to take a peek. There is a single point where the target will be in perfect focus, but in practice (as the paper shows) the target is "in-focus" enough in a larger region that your satellites can take a picture while they fly through the region around the ideal point.

ur-whale 4y ago
If all this effort is expended only to look at a single object, the whole idea seems kind of pointless. However, we are using the mental model of a camera lens to reach that conclusion, and I'm not certain it applies: 1) even if we use the mental model of a camera lens, given the distances involved, you can probably consider most of the interesting the targets to be "at infinity" 2) I'm not certain that a gravitational lens works like a camera lens.
- samus 4y ago
  It behaves differently of course, and the pictures would be massively distorted. But with some image processing it should be possible to do some analysis. One of the recent JWST images shows an example where a massive galaxy cluster makes redshifted galaxies behind visible.