> "If the image is too faint because of the signal to instrument precision (noise) ratio is too low, you will never get an image..." I'm curious why this makes

> "If the image is too faint because of the signal to instrument precision (noise) ratio is too low, you will never get an image..." I'm curious why this makes sense to you? Does it make sense that you could use an ordinary film camera and take a picture with an arbitrarily short exposure, say a picosecond? With very, very low SNR it can take a long time to build up data. The reason why this is possible is because the real data, the signal, is correlated with itself, it builds up consistently with each addition of measurements. Noise, however, is uncorrelated, it's random, so it tends to evenly cancel (or even) itself out with additional measurements.