It\'s difficult to compare two MTF charts in two separate PDFs when the scaling is different. I\'ve put them together for reference (the grid has been aligned so they should match). The red is the 21.
So the reading of this is that the 21 starts off sharper but the 25 takes over up until about 17-18mm (tangential) with a variation as to when the 25 takes over depending on resolution. As for tangential, they are identical at low resolution but the 25 significantly deteriorates at the two higher resolutions.
The conclusion that I draw here is that the main difference is in the tangential direction for medium and high frequency patterns. In short they are pretty much matched (the 21 being slightly better in the center and corners and the 25 being slightly better in mid frame) as far as the sagittal component is concerned as well as the low resolution tangential component. There is however a significant difference in the higher tangential radial components - meaning that the 21 can resolve finer detail.
As for comparing the 21 @ f/2.8 to the 25 @ f/5.6 - that\'s just silly.
Rather than talk about and interpret what others may or may not have said, first hand use of the lens may prove useful for you. Use it for its intended use, landscape, and for \"unusual\" or \"interesting\" image quality close up. Then form an opinion of the lens.
I prefer tests to anecdotal evidence - even if that evidence is my own. Having said that I really couldn\'t care less about the 25. Not interested in it the slightest. That was pretty much my point from the start but you and some others took offense at Lloyd\'s review which I referred to. Hence this discussion.
This specific topic of the sharpness follows Herb\'s claim that the 25 is sharper across the frame than the 21, which is to say the least a pretty controversial statement. I have been trying to find support for it and apart from the diffraction theory that I put forward I have not found anything - including the MTF charts - that would support it.
It\'s difficult to compare two MTF charts in two separate PDFs when the scaling is different. I\'ve put them together for reference (the grid has been aligned so they should match). The red is the 21.
So the reading of this is that the 21 starts off sharper but the 25 takes over up until about 17-18mm (tangential) with a variation as to when the 25 takes over depending on resolution. As for sagittal, they are identical at low resolution but the 25 significantly deteriorates at the two higher resolutions.
The conclusion that I draw here is that the main difference is in the radial (sagittal) direction for medium and high frequency patterns. In short they are pretty much matched (the 21 being slightly better in the center and corners and the 25 being slightly better in mid frame) as far as the tangential component is concerned as well as the low resolution radial component. There is however a significant difference in the higher resolution radial components - meaning that the 21 can resolve finer detail.
As for comparing the 21 @ f/2.8 to the 25 @ f/5.6 - that\'s just silly.
Rather than talk about and interpret what others may or may not have said, first hand use of the lens may prove useful for you. Use it for its intended use, landscape, and for \"unusual\" or \"interesting\" image quality close up. Then form an opinion of the lens.
I prefer tests to anecdotal evidence - even if that evidence is my own. Having said that I really couldn\'t care less about the 25. Not interested in it the slightest. That was pretty much my point from the start but you and some others took offense at Lloyd\'s review which I referred to. Hence this discussion.
This specific topic of the sharpness follows Herb\'s claim that the 25 is sharper across the frame than the 21, which is to say the least a pretty controversial statement. I have been trying to find support for it and apart from the diffraction theory that I put forward I have not found anything - including the MTF charts - that would support it.
Jun 09, 2010 at 11:28 PM
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