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p.2 #6 · p.2 #6 · Occurance of Aliasing (Moire) and Postprocessing... | |
I think the reason that pictures like the one posted here work (very little aliasing visible) is that the D800E has enough pixels that it can rely on the lack of quality of the Nikon lenses to act as an anti-aliasing filter.
That was a tad provocative, since the Nikon (Nikkor) lenses are very good quality and are generally as good as any in their class or so near that the differences have little consequence. The same principles would apply to other leading lens manufacturers.
Thus permit me to expand on my remarks. The high quality Nikkor lenses have limits (like every lens ever manufactured or that will be manufactured). Given the prices they must be sold at, those limits are high, but not stupendous.
I wasn't able to find lists of specific resolutions at line pairs per millimeter (lpm) of Nikkors, and MTF contrast at the lpm is important too. But I have some indication that top quality Nikkors can do about 80 lpm at 50% MTF contrast.
Think of a line pair as a single sine wave cycle, which is what it approximates at 50% MTF: gray to black to gray to white to gray. Thus it gives us the spatial frequency or rather the wavelength at that spatial frequency. One millimetre divided by 80 lpm = 12.5 micrometres per line pair.
The thing to note is that the dimensions of the D800E sensor are 7360 x 4912 pixels and (close to or exactly) 36 x 24 mm. Now, 36 mm = 36,000 micrometres. 36,000/ 7,360 = 4.89 micrometres per sensel (pixel) side.
The Nyquist frequency is half the sampling frequency. The sampling frequency is the pixel density. So two pixels (sensels) side by side must cover no more than one line pair or there will be aliasing and false image data created.
Two sensels span 2 x 4.89 = 9.8 or 10 micrometres. This is less than 12.5 micrometres per line pair. This is good.
Thus, it seems to me, even the best Nikkor lenses are good enough to challenge the sensor with no AA filter, but provide enough blur to act as the AA filter.
In practice, there is some resolution at less than 30 % MTF and thus some small amount of signal (image) will get aliased. But it will generally be overwhelmed by stronger signals of bolder image data or will be weak enough that the aliasing will not be visible under conditions that would cause aliasing with weaker sensors.
In practice, there may not be much difference between the D800 and D800E images. Where there is a difference it is likely to be unfavourable (jaggies and moire and aliasing artifacts).
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