RF24-70 & RF15-35 Reviews

Michael Clark

Now we see through a glass, darkly...
Apr 5, 2016
1,274
632
But that leads to one question:
If you are right here (R&D on field curvature), why do the RF primes look so well on flat field?

I would assume that Canon R&D would take the same primary IQ goals (field curvature sharpness) for lens design, even though primes and zooms are designed differently.
A well-recognized authority far more knowledgeable than I goes into fairly great detail to explain field of focus at the link in my above comment.

As to why RF primes look so well on flat field:

Because the makers of practically every new lens for the last half decade or so have sold their souls to the gods of the flat test chart. Why? Because most of the masses buying the majority of lenses on the market these days are too ignorant to realize that "sharpest" shooting a flat test chart does not always mean "best" for real world usage.
 

Larsskv

EOS 7D MK II
Jun 12, 2015
790
217
A well-recognized authority far more knowledgeable than I goes into fairly great detail to explain field of focus at the link in my above comment.

As to why RF primes look so well on flat field:

Because the makers of practically every new lens for the last half decade or so have sold their souls to the gods of the flat test chart. Why? Because most of the masses buying the majority of lenses on the market these days are too ignorant to realize that "sharpest" shooting a flat test chart does not always mean "best" for real world usage.
I agree! I for one love the images I get from the EF 50L and the EF 85LII. They make subjects look good in a way few other lenses can.

I sold my EF50L after getting the RF50L, but bought another one after a few months. I absolutely love the RF50L, but it hasn’t made the EF50L obsolete in my camera bag.
 

Joules

EOS 7D MK II
Jul 16, 2017
481
423
Hamburg, Germany
Buse most of the masses buying the majority of lenses on the market these days are too ignorant to realize that "sharpest" shooting a flat test chart does not always mean "best" for real world usage.
To be fair though, it is not just the people who have a hand in this. Reviewers could go through the trouble of finding the focus distance for points away from the center and measure the edge sharpness with subjects at these distances. Than they could publish edge sharpness and curvature measurements that are comparable... But at much higher effort. And is that effort worth it?

If I have subjects that stretch across the frame, like a tree or a group of people, there tends to be a single plane of focus that I would like to be sharp. I wouldn't want the tell the people that they have to align in some half circle, making some of the appear bigger and more important, just so that they don't get blurry.

Do we have an idea of how big the compromise between blur quality and focus flatness is?
 
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Michael Clark

Now we see through a glass, darkly...
Apr 5, 2016
1,274
632
To be fair though, it is not just the people who have a hand in this. Reviewers could go through the trouble of finding the focus distance for points away from the center and measure the edge sharpness with subjects at these distances. Than they could publish edge sharpness and curvature measurements that are comparable... But at much higher effort. And is that effort worth it?

If I have subjects that stretch across the frame, like a tree or a group of people, there tends to be a single plane of focus that I would like to be sharp. I wouldn't want the tell the people that they have to align in some half circle, making some of the appear bigger and more important, just so that they don't get blurry.

Do we have an idea of how big the compromise between blur quality and focus flatness is?
A well-recognized authority far more knowledgeable than I goes into fairly great detail to explain field of focus at the link in my above comment.

He has also published modified MTF charts for lenses in which the sharpest position (on his lab bench) is used for each position, rather than the position of the lens when the center is sharpest. In fact, he has included such tests and placed them side by side for the same lenses (he rarely tests fewer than ten copies of a particular lens model in order to reduce the influence of random lens-to-lens variation, and he tells us when he has used test results from less than ten copies of a lens model) in the article linked above.

 
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Michael Clark

Now we see through a glass, darkly...
Apr 5, 2016
1,274
632
To be fair though, it is not just the people who have a hand in this. Reviewers could go through the trouble of finding the focus distance for points away from the center and measure the edge sharpness with subjects at these distances. Than they could publish edge sharpness and curvature measurements that are comparable... But at much higher effort. And is that effort worth it?

If I have subjects that stretch across the frame, like a tree or a group of people, there tends to be a single plane of focus that I would like to be sharp. I wouldn't want the tell the people that they have to align in some half circle, making some of the appear bigger and more important, just so that they don't get blurry.

Do we have an idea of how big the compromise between blur quality and focus flatness is?
To be fair, though, if you "have subjects that stretch across the frame..." you may not want the same characteristics in a lens as folks who do not have subjects that stretch across the frame, but rather occupy one specific part of the frame and are more concerned with how the out of focus areas of the rest of the frame look than how sharp the lens is at the corners/edges when there is nothing but empty air in the corners/edges of the frame at the distance from the camera to which the lens is focused.
 
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navastronia

EOS RP + 5D Classic
Aug 31, 2018
293
322
To be fair though, it is not just the people who have a hand in this. Reviewers could go through the trouble of finding the focus distance for points away from the center and measure the edge sharpness with subjects at these distances. Than they could publish edge sharpness and curvature measurements that are comparable... But at much higher effort. And is that effort worth it?

If I have subjects that stretch across the frame, like a tree or a group of people, there tends to be a single plane of focus that I would like to be sharp. I wouldn't want the tell the people that they have to align in some half circle, making some of the appear bigger and more important, just so that they don't get blurry.

Do we have an idea of how big the compromise between blur quality and focus flatness is?
Great points, all of them.