Re: Canon 80D dynamic range: good news! (quick test with RAW ...
Let\'s be clear why f/8 AF has been problematic to start with. Phase detect AF works by looking at incoming rays of light from either side of the aperture. This is the baseline size and the bigger the baseline the more accurate the comparison of phase can be since you will have a bigger phase difference from these rays. Thus fast glass is always superior just for this reason alone. But alos think of what happens with smaller apertures in terms of the rays that can be accepted. The smaller the aperture the more paraxial the rays that can be focused by the lens, thus the phase difference will always be smaller on rays from either side of the aperture since they come from a much smaller region of object space. So even for the AF sensors that are in the centre they have to be more sensitive to be able to detect this smaller phase difference and why in the past only the high end cameras offered any AF at f/8 and even then only with the most sensitive dual cross-type centre point. As the AF sensor sensitivity improves and the signal processing power increases you can now have enough phase difference to analyze on AF points that are off-centre, but not too much so. The peripheral AF points are of course much more problematic as they rely on the phase difference in skew rays from further out from the lens centre and of course wider open these rays may suffer from vignetting which reduces their intensity and possibly other lens aberrations.
For Canon to achieve AF at f/8 with all points on the 1DX II is a truly impressive feat. For the 80D I presume it\'s a combination of less sensitive AF points and a lot less processing power for signal analysis, after all 1DX II has dedicated AF cpu and dual digic 6+, compared to 80D\'s single digic. As to why the 80D only allows of-centre AF at f/8 with two lenses is rather interesting. I can\'t see why say the 500/600 II + 2x would not work, but maybe it\'s to do with the final FL\'s of 1000 and 1200mm being just too paraxial since fov is only 1.7-2 degrees and maybe 800mm with FoV of 2.6 degrees allows just enough phase difference to be measured by the 80D. This is a small difference and maybe FW update down the track would change things.
Mar 24, 2016 at 05:28 PM
Previous versions of Pixel Perfect's message #13478608 « Canon 80D dynamic range: good news! (quick test with RAW images) »
