Continuous Field Image: Hubble Deep Field & Exoplanets

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Discussion Overview

The discussion revolves around the relationship between exposure time and image resolution in astrophotography, specifically in the context of the Hubble deep field image and the potential for observing features on exoplanets. Participants explore the implications of photon collection duration and the factors that influence image quality and resolution.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that increasing the duration of photon collection improves image resolution, questioning how much more resolution could be achieved with longer exposure times.
  • Another participant counters that resolution is not dependent on the number of photons but rather on the optical system's aperture size and pixel size on the sensor.
  • A further contribution indicates that the relationship between resolution and exposure time may be more complex, involving signal-to-noise ratio and bandwidth considerations, suggesting that basic rules of thumb may not capture the full picture.
  • Participants discuss advanced techniques that can mitigate limitations in pixel size and other factors affecting image quality.
  • There is mention of the Nyquist Criterion and its implications for data sampling, with a participant emphasizing the need to consider these rules on a case-by-case basis.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between exposure time and resolution, with no consensus reached on the extent to which longer exposure times contribute to improved resolution. The discussion remains unresolved regarding the implications of advanced techniques and theoretical limits.

Contextual Notes

Participants highlight limitations related to pixel size, signal-to-noise ratio, and the complexity of image processing techniques, indicating that these factors may influence the discussion but remain unresolved.

vinven7
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The Hubble deep field image was constructed by collecting photons from a specific region of space over a continuous duration of time; in this case ten days. As the number of collected photons increase, higher the resolution of the image.

If this duration increases, how much more resolution do you get to see? Specifically what if we had a continuous field of view of a certain galaxy - is there some distance for which you could see things in very high definition? Would we be able to see features on exoplanets ? This is of course a function of distance from us, but I am curious to know what kind of information we have about this.
 
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vinven7 said:
As the number of collected photons increase, higher the resolution of the image.

The resolution does not depend on the number of photons. Instead, the 'quality' of the image increases as you gather more light. A short exposure is very 'grainy' and has a low signal-to-noise ratio compared to a long exposure.

vinven7 said:
If this duration increases, how much more resolution do you get to see?

None. :wink:

Resolution is a function of the size of the optical system, specifically the diameter of the aperture, and the size of the pixels on the sensor. Smaller pixels give higher resolution, as long as your optical system can bring the size of the airy disk down to approximately the same size as the pixels or smaller.
 
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Drakkith said:
The resolution does not depend on the number of photons.
That statement could be over-simplified. Basic signalling theory tells us that the limit to resolution depends, not only on the (spatial) bandwidth but on signal to noise ratio. The basic Raleigh criterion is only a rule of thumb. The shape of the dip between two peaks can be refined and refined without limit by integration over a long time. Shannon tells us that the apparent limits, due to pixel size (spatial sampling rate) and aperture can always be exceeded by reducing the bandwidth of the system enough.
This is 'only' an extension of what every good amateur Astrophotographer can get by stacking dozens of images from a light polluted urban environment; a bit more sophisticated than that, though.
 
sophiecentaur said:
That statement could be over-simplified.

I suppose. I wasn't thinking of some of the advanced techniques that can be used to make up for limitations in pixel size and other factors.
 
Drakkith said:
limitations in pixel size
That's only a form of sub-sampling which, for non periodic data, can run a coach and horses through what we think of as gospel - ie, The Nyqyuist Criterion. Rules of thumb need to be treated on a case by case basis. :smile:
 
Ah, well, there you have it then. :wink:
 
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