Out-resolving issues

[Eric Borgström]

Could someone please explain what lens out-resolving the sensor does to the image.
With new mega pixel sensors we might have the opposite, sensor out-resolves the lens. That probably gives different issues with the image.
And perhaps in the center of the image the lens is out-resolving but in the periphery the sensor might win out.
Who knows about this?

[Bjørn Rørslett]

Basically you get increased moiré or spurious resolution. Or both.

Spurious resolution makes strange artifacts when you shoot say a ruler. Some of the division tics will appear dislocated.

[Eric Borgström]

Thank you Bjørn.

[Les Olson]

Spurious resolution is due to image defocus, not sampling frequency.  There is a good example and lucid explanation at http://toothwalker.org/optics/spurious.html 

[Bjørn Rørslett]

Aliasing generates spurious resolution.

[Les Olson]

Aliasing generates spurious resolution.

No, aliasing is when high frequencies are reconstructed as lower frequencies because of under-sampling - "moire".  There are elegant simulations at http://micro.magnet.fsu.edu/primer/java/digitalimaging/processing/samplefrequency/index.html and http://micro.magnet.fsu.edu/primer/java/digitalimaging/processing/undersampling/index.html

Spurious resolution is quite different.  It was observed long before digital imaging, in aerial reconnaissance where variations in altitude cause de-focus, and explained in the early 1980s.  There is a simple demonstration in Figure 1 of https://www.researchgate.net/publication/253579540_Correcting_spurious_resolution_in_defocused_images_-_art_no_64920O

[Bjørn Rørslett]

The phenomena are clear, the terminology perhaps not. If you wish to reserve 'spurious' for one particular kind of false resolution it's fine with me. As I'm not a native English speaker I bow to the better informed.

I tried to avoid 'moiré' as that concept so often is associated to colour artifacts while the aliasing concerns any [spatial or other domain] frequency not sufficiently sampled.

[David H. Hartman]

Spurious is English for Latin spurius meaning false.

Not being what it purports to be; false or fake.

Hope this helps,

Dave