- #36

collinsmark

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It's very misleading because, in a real image there is not a point source and also there are a number of other sources in the vicinity of the low level parts of a diffraction spike. this constitutes a 'floor' which can be significantly above the least significant step in the ADC.

If a pixel lies along the path of diffraction spike, and is dim enough such that expected value for that pixel is less than 1 analog-to-digital converter units (ADU) after compensating for noise (dark frame subtraction), there is still a finite probability that the pixel will register 1 or more ADU. For example, for a given exposure time, in a dim section of a diffraction spike, a pixel might only have a 50% chance of registering a single ADU or more. On even dimmer section of the spike, the probability drops to 25%. This is due to probabilistic nature of shot noise, which is inherently part and parcel of the signal. In other words, if you look along a diffraction spike in the vicinity of 50% probability, half of the pixels in that region will register at least 1 ADU above the noise (i.e., ~1 ADU after dark frame subtraction).

The point is that even if the expected value of a pixel that lies in a diffraction spike is less than the least significant step in the ADC (i.e., 1 ADU), it does

*not*guarantee that the pixel will not register a signal. The signal

*still*has an effect on the pixel registration in a probabilistic manner.

[Edit: and if a particular pixel is along the intersection of diffraction spikes/artifacts, say from two or three or more different stars, the probabilistic contributions add together linearly, even if the expectation value of anyone of the spikes/artifacts, or all of them, is less than 1 ADU in that region.]

And you don't need a point source for this. As I've essentially stated in post #404 the interference pattern applies to

*all*photons that pass through the optics and reach the detector, whether those photons originate from stars, nebulosity, accretion disks, anything. Any photon that passes through the telescope's optics is subject to an interference pattern before that photon reaches the sensor, if it reaches the sensor at all. It matters not what the source of the photons are for this. All photons from any distant source that reach the sensor are subject an interference pattern before reaching the sensor.

There's nothing misleading about this. Diffraction patterns and interference patterns and the probabilistic nature of quantum mechanics are not "misleading." It's just how the universe works.

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