Thanks Pawel, lots of new ground for me there to cover :-)
The 'very high-frequency components (sharp edges)' referred to above, the limits of human vision, can that be plotted on your MTF chart above for comparison purposes?The modulation transfer function (MTF) represents the Bode plot of an imaging system (such as a microscope or the human eye), and thus depicts the filtering characteristic of the imaging system. The human eye, for instance, acts as a low-pass filter, in that very high-frequency components (sharp edges) cannot be perfectly perceived.
Again, from Wiki;
The 'roll-off' in corner sharpness is clearly evident on your MTF chart, and although the Nikonos displays superior performance, it seems, to me anyways, far from ideal. Where would the 10.25" dome plot fall? Just out of curiosity, what lenses were used behind the flat and dome ports for your test, were they set at their optimum F-stops?Factors affecting MTF in typical camera systems
In practice, many factors result in considerable blurring of a reproduced image, such that patterns with spatial frequency just below the Nyquist rate may not even be visible, and the finest patterns that can be seen appear 'washed out' as shades of grey, not black and white. A major factor is usually the impossibility of making the perfect 'brick wall' optical filter (often realized as a 'phase plate' or a lens with specific blurring properties in digital cameras and video camcorders). Such a filter is necessary to reduce aliasing by eliminating spatial frequencies above the Nyquist rate, but in practice, it will have a response that 'rolls off' seriously before the Nyquist frequency is reached.
I am beginning to realize that the only solution for the 'perfect' underwater image, may lie in designing a sensor physically constructed to mirror the image field curvature of the intended dome. In other words, a dedicated underwater sensor, just as the Nikonos is a dedicated underwater lens.
The Dome Sensor. You heard it here first folks