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Originally Posted by [1ponders]
So Dennis according to the chart, by increasing FL using barlows or eyepiece projection then the pixel size needs to increase.
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Yes – I think that’s correct.
Let’s look at a simple white square of sides 10 cms x 10 cms. There is no detail inside the square; it is a 10 cm white square, that’s it.
Now, if we use a ccd chip that takes say, 9 pixels to represent this square, then mostly those pixels are wasted, as each pixel is only resolving a smaller white square but there is no additional detail at that smaller resolution. This means we are dedicating those 9 pixels to reading “no additional data”, and then we also have to read the pixels and transfer the “empty” data to our PC. This is wasteful of our precious pixels and bandwidth and is termed over sampling.
I think the Niquist theorem says something like x2 pixels of 10x5cms would be the optimum required to correctly gather the data for the 10cm white square and of course, we would then only be using 2 of our precious pixels, not 9, and the data readout and traffic would be more optimal too.
Now if we move in the other direction and say use a pixel 15cm x 15cm, then the 10cm x 10cm white square would easily fit inside this larger pixel but the pixel would display as a 15cmx15cm pixel on our display and so we would effectively “lose” the resolution of our 10cmx10cm square – we are now under sampling. That is, we are not seeing our 10cmx10cm white square, we are viewing a 15cmx15cm pixel with the square “hidden” inside it.
Anyhow, that’s my layman’s understanding. I’m sure the mathematically minded and scientifically trained readers will correct me where I am wrong.
Cheers
Dennis