Lens and Sensor Resolution

Started 7 months ago | Discussions thread
The Ghost of Caravaggio Contributing Member • Posts: 926
The Lens Is One Of Many Factors

I suspect any MTF90 deficit in lens performance compared to sensor capability is much smaller than other factors that determine perceived image sharpness.

Perceived image sharpness is complicated.

Imatest offers a useful document that serves as an introduction to the modulation transfer function, MTF as well as other methods to evaluate perceived image sharpness..

This blog post discusses the issues. The author provides evidence that MTF 90 rather than the commonly used MTF 50 is more relevant for human perception.

The MTF 90 (or 50) for a given image depends on every stage during the image creation process. Lens resolution is only one of these.

Pixel peeping is not real life.

The MTF 90 of the printer and printer paper can be the limiting factor in perceived image sharpness. The same goes for digital viewing options. A significant factor is: how do you expect people to view your images. Strangers viewing them on-line may never be able to take advantage of a high resolution if the the MTF 90 for their viewing device is low. For prints, viewing distance is has a mofiir impact and is uncontrollable.

Some of us rely on cropping to affect composition. In this case the lens MTF and sensor resolution become more important. However there unavoidable factors that degrade MTF 90 such as atmospheric distortion (heat waves) and haze. Lens flare is another variable. In some scenarios not using a lens hood could be the limiting factor in perceived sharpness.

Image rendering has a significant impact on perceived sharpness. Sub-optimal rendering parameters used for either in-camera or ex-camera rendering can degrade perceived sharpness. There are three types of post-production sharpening to consider:

  • Capture sharpening - restores detail lost in capture
  • Creative sharpening - local adjustment of sharpness
  • Output sharpening - adjusting for the output, like compensating for ink spread.

Illl-chosen noise filtering (a.k.a noise reduction) parameters are another rending error that could unnecessarily degrade perceived image sharpness.

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"The belief that ‘randomness’ is some kind of real property existing in Nature is a form of the mind projection fallacy which says, in effect, ‘I don’t know the detailed causes – therefore – Nature does not know them."

E.T Jaynes, Probability Theory: The Logic of Science

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