Earth Observation GEO Refractor Telescope?

[AerospaceAsh]

Hi guys,

I'm relatively new to telescopes and optics.

I am curious Earth Observation GEO refractor telescopes. We have issues with magnification because of the atmosphere, Dawes' Limit, etc.

If I had a refractor telescope in GEO orbit looking back at the Earth, how many of these problems still stand? If I could get something large enough to produce, say 10000x magnifcation, assuming we could get the telescope up there, what's stopping it from being optically practical with such high magnifications?

E.g. Let's say I have an object diamter of 300mm, a focal length of 15000mm, f ratio 50, and an eyepiece focal length of 1.5mm ... that gives me 10000x magnification, power per inch aperture of 847, exit pupil of 0.03mm, true field of 0.005deg. Obviously we have a camera instead of an eye regarding exit pupil.

Is there an issue with such a step, e.g. power per inch aperture? I'm just looking for some sanity checking.

Thanks,

Ash

[AerospaceAsh]

Should've checked for typos! Apologies!

[pete_l]

Is there an issue with such a step, e.g. power per inch aperture? I'm just looking for some sanity checking.

The telescope would still be subject to the basic physics of diffraction. Ultimately that would limit its resolving power.

It's my understanding that what we see (or what our cameras record) as a point is, in reality, an Airy disk with a bright centre that we call "the target" and a series of exceedingly dim concentric rings that for all intents and purposes are noy visible (though we see them when the telescope is purposely defocused). As the magnification gets higher - even when the telescope is perfectly focused, the central disk becomes a smaller part of the image and more of the light is dispersed into the rings. Hence there is a fundamental limit (set by the aperture) to a telescope's resolution.

[ronin]

The optical systems that the satellites have will be "extreme" to say the least, the surfaces will not be spherical, which is what we are used to. Eyepieces are starting to use Aspheric elements but these are difficult as they tend to be cast and you do not get the clarity and lack of imperfections - I guess a high percentage of the cast elements are scrapped.

Theoretically they may not even be the same refractive index across the lens - that is difficult or impossible to do but the results are "interesting" from the theory. You can get a point and the first airy disk can be pushed out from the central point image such that it is off the sensor. So what you get is the point image and no airy disk. Your central point is lower in energy and there is more in the off sensor airy disk but that is of little consequence.

A lot of what is "seen" is the result of applying software to the real image, as you know what aberrations and limitiation occur you can in effect correct for them by software.