by Chris Peterson » Thu Aug 27, 2009 2:16 pm
geckzilla wrote:I don't understand why the streaks are so crisp. I don't think they are any kind of flying debris but I don't understand why they are in focus, either. Which part is damaged?
They are classic cosmic ray hits on the CCD. I get them all the time on my images, and the rate is higher in space. Sometimes the high energy particles directly hit the CCD, which usually creates a really messy splash. Most often, they first strike something else, like the CCD chip packaging, surrounding camera structure, etc, and this produces a shower of lower energy particles- one or more of which may strike the sensor. When that happens they can dump a charge into one or more pixels, which shows up as a white point or a white streak. They appear to be in focus because they are affecting the pixels directly, and there is a sharp boundary between affected and unaffected pixels. Of course, there are no optics involved so "focus" really has no meaning.
[quote="geckzilla"]I don't understand why the streaks are so crisp. I don't think they are any kind of flying debris but I don't understand why they are in focus, either. Which part is damaged?[/quote]
They are classic cosmic ray hits on the CCD. I get them all the time on my images, and the rate is higher in space. Sometimes the high energy particles directly hit the CCD, which usually creates a really messy splash. Most often, they first strike something else, like the CCD chip packaging, surrounding camera structure, etc, and this produces a shower of lower energy particles- one or more of which may strike the sensor. When that happens they can dump a charge into one or more pixels, which shows up as a white point or a white streak. They appear to be in focus because they are affecting the pixels directly, and there is a sharp boundary between affected and unaffected pixels. Of course, there are no optics involved so "focus" really has no meaning.