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Old Sep 20, 2009, 2:43 AM   #21
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The diffraction limit has nothing to do with the quality of a lens; it's a limitation imposed by the physics of light. Since most lenses are sharpest at around f/8.0, I referred to the diffraction limit of f/11 to give a lens a little leeway in its use. To be sure, the diffraction limit is only one obstacle in optics, but it's the only one that's insurmountable.
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Old Sep 20, 2009, 4:30 AM   #22
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The diffraction limit has nothing to do with the quality of a lens; it's a limitation imposed by the physics of light. Since most lenses are sharpest at around f/8.0, I referred to the diffraction limit of f/11 to give a lens a little leeway in its use. To be sure, the diffraction limit is only one obstacle in optics, but it's the only one that's insurmountable.
I said that if the lens quality is high enough, then the only thing limiting its performance is diffraction limiting. This is known as a "diffraction limited lens".

If the lens is high enough quality, then it can be sharper at a larger aperture, reducing diffraction, and increasing the ability to resolve detail.

In the case of digital cameras, this translates to the ability to resolve detail compared to the resolution of the sensor.

For F11, FF sensor, the diffraction will limit the resolution to less than 20Mpixel.
For F4, FF sensor, the diffraction will limit the resolution to around 120Mpixel.

This is what I meant by diffraction limited.

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Old Sep 20, 2009, 5:59 AM   #23
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But the SYSTEM is not diffraction limited. Improving sensor resolution, even in a system that is using a diffraction limited lens can still improves the overall quality at the end of the chain.
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Old Sep 20, 2009, 8:45 AM   #24
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For F11, FF sensor, the diffraction will limit the resolution to less than 20Mpixel.
The diffraction limited f-stop on the FF 24MP Sony A900 is f/19.0.
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Old Sep 20, 2009, 9:56 AM   #25
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But the SYSTEM is not diffraction limited. Improving sensor resolution, even in a system that is using a diffraction limited lens can still improves the overall quality at the end of the chain.
A "Diffraction limited lens" is the best quality lens, meaning that the limiting factor of the lens is diffraction only, not any other optical factor.

If the system has 24Mpixel full frame sensor, and the lens is almost perfect (i.e. it is diffraction limited), then diffraction limited F stop is around F9.
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Old Sep 20, 2009, 9:59 AM   #26
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The diffraction limited f-stop on the FF 24MP Sony A900 is f/19.0.
Your source obviously differs, because I make that about F9.
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Old Sep 20, 2009, 8:50 PM   #27
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"Full Frame" is a term thrown out a lot, as is diffraction limitation. A full frame sensor of 16x20 inches with a normal lens has a diffraction limit f/stop is something like F/128 or smaller.

And yes, 16x20 inch sensors do exist: it is called sheet film. Normally cut into 4 - 8x10" or 16 - 4x5" sheets and properly notch coded.
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