Patrick.C.F.Lee 於 2010 年 4 月 15 日 上載

Flying Bird

The first times to shoot a flying bird with reasonably good picture quality. I am really happy because a 3X optical zoom entry level DC can shoot a flying bird. Thanks to AGFA for offering shutter priority mode to this entry level digital camera, otherwise I cannot freeze the flying even using sports mode. Even though shooting at almost 9 mega pixels, the picture quality is not quite good because the aperture of the lens is too small so that the true resolution is about only 2.1 mega pixels for the green light due to the diffraction (The calculation is based on the Airy disk which assumes the aperture is a circle, however, the apeture of my camera is likely a polygonal (except at full open). Also one must remember the Bayer Array of CCD photosites on the image sensor: 1R + 2G + 1B. Hence, the green light reaches the diffraction limit earlier than the red light even though the red light has longer wavelength. The diffraction limit the resolution of red light to 2.34 mega pixels). Hence, once I crop the photo, the picture qualtiy degrades as the photo is watching at 100% size on the computer monitor.

Correction: The above popular conclusion, namely, green light limits the useful resolution for Bayer Array CCD, is actually incorrect. Now, I have studied the issue throughtly and disagree with the above popular conclusions. For the sensor of my camera, the resolution for the green light at f-number f/5.6 is 2.94 mega pixels. So the red light is still the light that limits the resolution of my digital camera due to diffraction.

The older AGFA Photo 1033m (which is also far cheaper than HK$ 1000) has a larger lens and can produce a better picture quality for this picture (This older camera will shoot at f/5.2 rather than f/5.6; so the diffraction will be significant smaller). Overall , my camera is really good (in particular, the colour is excellent) with only 2 major drawbacks:
(1) The lens is too small (although the quality of the lens is very good). A lot of 5 years old entry level digital cameras from various vendors have larger lenses.
(2) It is too complication to change the settings. The older AGFA Photo 1033m has a switch to switch among the Av, Tv and M mode so that it is much faster than my camera for shootings that require.changing the settings.

Anyway, I cannot complaint to much on my HK$ 499 digital camera.

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