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A comment on Hubble takes gigantic image of the Triangulum Galaxy. Parent comment

Re:Hubble takes gigantic image of the Triangulum Galaxy by jstanley on Thursday January 10, 2019 @02:47AM (#18872231)
Imagine you have a camera 2.7m ly away from a star that is 2 billion km across, and it's the only significant light source in that direction.

How many pixels would you expect the image of the star to be? It can't be less than 1. You'd still see the individual star even though it is a lot smaller than 1 pixel. Imperfect optics mean it will likely appear larger than 1 pixel.

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Re:Hubble takes gigantic image of the Triangulum Galaxy by pjc50 on Thursday January 10, 2019 @04:47AM (#18872673)
Conversely, how many stars are contributing to that pixel?
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Re:Hubble takes gigantic image of the Triangulum Galaxy by varjag on Thursday January 10, 2019 @03:41AM (#18872434)
Easily. Which focal length/field of view lens is on that camera?
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Re:Hubble takes gigantic image of the Triangulum Galaxy by TheSpiceIsLife on Thursday January 10, 2019 @06:07AM (#18873010)
I would have thought all these stars and galaxies are at optical-infinity?
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Re:Hubble takes gigantic image of the Triangulum Galaxy by EForEndeavour on Thursday January 10, 2019 @11:35AM (#18875148)
True, and focal length is in fact defined (or at least thought of) under the assumption of parallel light rays coming in from an optically infinite distance. https://en.wikipedia.org/wiki/Focal_length
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Re:Hubble takes gigantic image of the Triangulum Galaxy by varjag on Friday January 11, 2019 @09:36AM (#18883794)
Yes? The sensor is not at optical infinity however, and the focal length determines the field of view you get. Quite clearly, one pixel of a camera with 0.001 degree angular resolution and the one of 10 degree FOV give you very different results.
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