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Old 16-11-2012, 04:37 PM
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strongmanmike (Michael)
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Focal length vs smaller pixels

Ok, I've been thinking about this and think I know but I thought I would throw this out there to get some other opinions...

My question is: Is there any difference, as far as real feature resolution in the final image, between doubling your focal length with the same size pixels and halving your pixels size with the same focal length?

The resulting image scale (arc"/pixel) is the same

Mike
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Old 16-11-2012, 05:10 PM
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Would have thought that ignoring seeing and field of view differences, and assuming perfect tracking that the two images would have identical resolutions.

Also assuming all you change is the focal length because the aperture would affect resolution.
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Old 16-11-2012, 05:28 PM
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One big factor in play would be the well depth of the smaller pixels. Generally 9 micron pixels have around 100000 electron depth, 5.4 micron around 25000.

Thats why kaf8300 chips tend to bloat stars.

Brett
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Old 16-11-2012, 07:27 PM
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Wider aperture means not only more light, but also delivers finer resolution, see here for more info:
http://en.wikipedia.org/wiki/Angular_resolution

In principle, when optical system is limiting factor, to achieve higher resolution, you must go with longer FL (and wider aperture).
Otherwise it is better (cheaper) to go with smaller pixels.
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Old 16-11-2012, 08:36 PM
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Yeah I agree with Brett.

The difference would be in the performance characteristics of the chips rather than the focal length etc.

Smaller pixels usually mean smaller well depth and perhaps higher noise in CCDs (not necessarily in CMOS where most of the research dollars go as Sony Exmor sensors have demonstrated very clearly).

Greg.
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Old 16-11-2012, 10:41 PM
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Cheers guys, nothing ground breaking there as I expected

Bojan, aperture was not a variable here only the focal length and the pixel size.

The small full well bloating stars doesn't sit comfortably with me...is this a real or imagined phenomena?

Mike
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Old 17-11-2012, 12:11 AM
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Quote:
Originally Posted by strongmanmike View Post
The small full well bloating stars doesn't sit comfortably with me...is this a real or imagined phenomena?

Mike
Small well depth was my main reason for moving from an 8300 to an 11002.
Binning RGB on the 8300 usually resulted in lost star colour for me rather than bloated stars.
The readout pixels are the same depth as the imaging pixels.
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