Quote:
Originally Posted by Peter Ward
No problemo. 
The bucket analogy goes further (at one stage CCD's were nearly called BBD's, literally: Bucket Brigade Devices) .
It also gives good insight understanding the the dynamic range of various sensors.
Our two rain..( al la photon...) gauges, one made from a bucket, the other a cup, hold x-ml of water.
Let's say it was really raining and we captured 12cm of water...our cup is overflowing (saturated ...) so we really don't know how much rain fell...but our bucket still has a good deal of volume left before it fills so we can still quantify the downpour.
Not only that, but our (big pixel) bucket holds a good deal more water, so the number of millilitres (photons) we can measure, from empty to full, is in the thousands, compared to our cup which can only hold a few hundred at best.
In short big pixels give more signal and higher dynamic range... the rub is: to get good (angular) resolution, you'll also need big optics. |
C'mon Peter - you don't seriously expect me to let that lot go through to the keeper do you?
Your analogy ran out of steam on the first post because it conveniently does not include noise - which, as you well know, is the other part of the dynamic range measure. A small chip will have smaller wells, but the reduced real estate makes it possible to also reduce the noise - small chips can have good dynamic range.
If we look at the dynamic ranges of a few chips from published well depth and read noise data we find:
K8300 = 2700:1
icx694 = 4000:1
K11002 = 4500:1
K16803 = 11000:1
The icx694 is right up there with the competition, despite its small pixels. The only one it does not compete with here is the 16803, but a camera with that chip can, by itself, cost more than an entire system built around an 8300 or a 694. There have been some beautiful images produced by 8300s and 11002s - on that basis, the 694 has ample dynamic range.
"
In short big pixels give more signal and higher dynamic range". ???? It has been shown above that the dynamic range of small pixel chips need not be significantly lower than that of large chips. And you conveniently forgot the bit about "but only if you use the same scope" when referring to the "more signal" bit. There is nothing inherently more sensitive about big pixels - they just intercept more photons in a given geometry than small ones so you gain sensitivity
and lose resolution. If the pixel scale is matched to give the same resolution, small pixels on a short focal length scope give just as much signal as large pixels on a long focal length scope. I am sure you know this - why confuse the issue?
So what you should have actually said in your throwaway sentence is: "In short, small pixels give the same signal and about the same dynamic range as similar bigger ones when both are matched to scopes of appropriate focal lengths and with the same aperture". And that excludes the fact that the 694 has higher QE than the competition.
Regards Ray