Sensor vs lens resolution Q or how many pixel needed to resolve 1 LP ?

Started Jun 13, 2012 | Discussions thread
Great Bustard
Forum ProPosts: 20,765
The question, as posed, is unanswerable.
In reply to Al_10D, Jun 13, 2012

Al_10D wrote:

The best Canon lenses resolve abput 60 lp/mm (according to DXOMARK) or 1440 lp per height and 2160 lp per width of FF sensor.

Like all "lens" tests, DxOMark's "lens" tests are system tests. That is, how well does a particular lens resolve on a particular sensor of a particular size with a particular number of pixels and a particular AA filter.

I wonder how many pixel needed to match the lens resolution?

An infinite number of pixels. Typically, system resolution is calculated as follows:

1 / (R system)² = 1 / (R lens)² + 1 / (R sensor)² + 1 / (R low bypass filter)² + ...

The system resolution is limited by the lowest resolution of the elements in the imaging chain. So, for the system resolution to match the lens resolution, the lens must be the lowest resolving portion of the chain, and the other elements in the chain have to be perfect not to result in less resolution still.

Is it 3 pixels per lp? If so, 28Mpx sensor resolution would be alredy limited by lens.

The question is not answerable unless we know the resolutions of all the elements in the chain.

However, the Canon 50 / 1.4 macro on a 5D2 (21 MP FF):

is resolving 3740 lw/ph in the center of the frame at 50% contrast with the processing (coversion) that PZ has applied to the photo, which is 78 lp/mm on the sensor, and 3.7 lp/mm on a 20x30 inch print.

Compare and contrast with the 50D (15 MP 1.6x):

where we have 2598 lw/ph in the center, and thus 2.6 lp/mm on a 20x30 inch print vs the 350D (8 MP 1.6x):

where it falls to 2064 lw/ph in the center, and thus 2.0 lp/mm on a 20x30 inch print.

So, on 1.6x, we see that an 87.5% increase in the pixel count resulted in a 26% increase in resolution, and a 60% increase in sensor width combined with a 40% increase in pixel count results in a 44% increase in resolution. At least, in the center, and at the sharpest aperture for the center.

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