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Originally Posted by davidpretorius
i like to pretend i understand this! naaagh,i don't!
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Hi Dave
Pardon my rudeness for not explaining the images more clearly, I was kinda just thinking out aloud at the time.
I once read a nice explanation of a ccd chip, where the writer likened the chip to a paddock (in Tasmania) filled with an array (rows and columns) of buckets. When it rains, each bucket will collect a number of rain drops; some more, some less.
This is analogous to the individual photo sites on the ccd chip that collect photons rather than rain drops. So, the first image with lots of multi coloured spikes is a 3-D representation of how many photons have been collected by the entire ccd chip at each photo site.
The number of photons counted at each photo site is then converted to an image on the computer screen, made up of pixels. Each pixel on the screen represents one photo site on the chip. In my case, with the SBIG ST7 ccd camera, the chip has 765 x 510 photo sites (also known as charge wells) that collect photons and so when the image is drawn on the screen, you get an image of 765 x 510 pixels.
So, what the CCDSoft camera control software has done is to paint a picture of the 765 x 510 image captured by the ccd chip in a 3-D colour map. I think my ccd camera can hold a range of 0 to over 65,000 drops of water in any one of its buckets. Because the screen cannot display 65,000 colours, the software has said something like;
“I’ll display 0 to 1000 drops of water as red”
“I’ll display 1001 to 5000 drops of water as green”
“I’ll display 5001 to 10000 drops of water as blue”
“I’ll display 10001 to 15000 drops of water as yellow”
“I’ll display 150001 to 20000 drops of water as pink (the colour of your tutu!)”
…etc., right up to the largest count which in the 3-D graph is brown or a dirty green colour.
For the other three images, I cropped a single star from the full ccd image and ran the 3-D plot on the individual star alone. I then rotated the plot, as best as I could, as if I was looking down on the star from above, a bit like looking at the contours of a hill or mountain on a map.
The purpose of this? Bored with the jets stream; bored with the clouds and rain, so I thought I would experiment and see if I could use these contours as a representation of the collimation of my scope. Nice, concentric rings would indicate good collimation. Off set rings would indicate not so well collimated.
Hope I haven’t confused you any more!
Cheers
Dennis