more pixels are better!

Started Dec 14, 2008 | Discussions thread
ejmartin Veteran Member • Posts: 6,274
Re: To be more specific...

Ralf Ronander wrote:

Not to argue against your conclusions,
but the shots are too different for a meaningful comparison.
Different object sizes (50D downsampled image vs 40D), different
lenses and different exposure. Deeper shadows in the 50D image.
Different object placement (in the right hand part of the image).
Possibly the latter could be in fovour of the 50D (the scale better
placed in the focal plane) but the other factors are mostly in favour
of 40D.

The use I was making of the two images was mainly for a noise comparison; for that purpose they are eminently suited. If I had the two cameras in hand I surely would have made the exposures, lenses etc equal. But that is irrelevant for noise, so long as one chooses two patches of the image of equal tonality in the two images. I'm not sure why aesthetic factors such as object placement, tone curve etc should matter as long as one is comparing say a white patch of tonal value 200 in one image to a white patch of tonality 200 in the other for the purpose of determining the noise spectrum of each.

A different set of images (the IR multitarget shots) were used for a resolution comparison using Imatest, and showed that both cameras have a similar ratio of MTF50 to Nyquist. For this test it is important that the camera be properly focussed on the test chart; it seemed to be.

Once one has determined that the noise spectrum is identical at comparable scales and the resolution is close to the ratio of pixel pitches, I think it reasonable to conclude that

1. Both sensors have the same quantum efficiency, and therefore the higher resolution sensor is not noisier than the lower resolution sensor, since they are gathering the same number of photons overall in each part of the image.

2. The higher resolution sensor has the potential to deliver higher image resolution in proportion to the linear pixel count, ie the camera does not limit increase of image detail (though other factors such as lens diffraction, camera shake, poor light, etc might).

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