Zeiss "Batis" AF lens line to be released for FF E-mount
Tariq Gibran wrote:
The degree of interpolation required for the actual distortion correction as well as the amount required in the subsequent resizing process (since a lens with greater distortion will undergo more cropping) will mean the magnitude of optical lens distortion is directly related to resolution loss during correction. More correction and thus heavier interpolation results in more resolution loss. How the distortion is distributed throughout the image will also be a factor (if it\'s mostly off axis, the center will be less impacted than the borders/ corners). Another consideration might be what effect correction has on bokeh. For instance, we might get oblong shaped bokeh off axis (is this what we are seeing with this Zeiss 85 in the sample images?)
Unless they\'ve done it in a very lazy way the distortion correction and resize operation will be implemented as a single transformation, but the result is the same and you are right that the degree to which the centre of the image ends up being enlarged depends on how much of the image area is lost which in turn depends in part on the magnitude of the distortion. It also depends on the type of distortion, pincushion distortion correction does the opposite and makes the image larger so no loss occurs.
The bokeh, compression artifacts and everything else will be distorted in the corners by the corrective transformation. Whether you will really see an impact in the bokeh I don\'t know, as the bokeh will be non-circular in the corners of a fast 85mm lens anyway due to viewing the entrance pupil from an angle (resulting in hard vignetting from the lens barrel).
alundeb wrote:
The magnitude of the resolution loss is 13% in the center while correcting less than 4% distortion. I discussed this with Roger when he published the blog post, and he agreed that the resampling itself contributes more than the stretching.
This is absolutely correct, Tariq\'s point was just that the amount of resizing depends on the distortion thus a 4% distortion lens loses more resolution in the centre than a 2% distortion lens, even though the distortion correction itself (the straightening of curved lines) is not the principal cause.
Re: Zeiss "Batis" AF lens line to be released for FF E-mount
Tariq Gibran wrote:
The degree of interpolation required for the actual distortion correction as well as the amount required in the subsequent resizing process (since a lens with greater distortion will undergo more cropping) will mean the magnitude of optical lens distortion is directly related to resolution loss during correction. More correction and thus heavier interpolation results in more resolution loss. How the distortion is distributed throughout the image will also be a factor (if it\'s mostly off axis, the center will be less impacted than the borders/ corners). Another consideration might be what effect correction has on bokeh. For instance, we might get oblong shaped bokeh off axis (is this what we are seeing with this Zeiss 85 in the sample images?)
Unless they\'ve done it in a very lazy way the distortion correction and resize operation will be implemented as a single transformation, but the result is the same and you are right that the degree to which the centre of the image ends up being enlarged depends on how much of the image area is lost which in turn depends in part on the magnitude of the distortion. It also depends on the type of distortion, pincushion distortion correction does the opposite and makes the image larger so no loss occurs.
The bokeh, compression artifacts and everything else will be distorted in the corners by the corrective transformation. Whether you will really see an impact in the bokeh I don\'t know, as the bokeh will be non-circular in the corners of a fast 85mm lens anyway due to viewing the entrance pupil from an angle (resulting in hard vignetting from the lens barrel).
Apr 30, 2015 at 07:36 AM
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