Stellar lens, no weak spots

FingerPainter wrote:

Sittatunga wrote:

FingerPainter wrote:

gimp_dad wrote:

FingerPainter wrote:

Well the edges (not even corners) at f/4 and f/5.6 at 100mm are so weak I certainly would be forced not to use this lens for certain shots.

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I’m not seeing softness near the edges at 100mm with my copy of the RF70-200/4LIS. FingerPainter, can you share your examples of this phenomenon? I wonder if you have a bad copy.

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Check online reviews that actually measure lens sharpness.

I'm confused. Wouldn't it be easier to present the results of your own tests for this, or for field curvature at a number of subject distances than to tell people to check unspecified online reviews?

Of course not. Doing a proper set of tests requires certain equipment and adherence to a rigorous process. It is much easier to rely on people who have proven over time that they know how to conduct tests than it is to acquire the equipment, and develop the expertise to conduct tests oneself and then to spend the time actually conducting a thorough test.

I think most people who conduct and rely on their own tests foolishly overestimate their ability to produce tests that give meaningful results. I'm not so foolish to think I can do as good a job as certain review sites.

But you haven't named one of them or given any specific references that we can check. Until you do, it's the word of someone who makes no claim to actually having used the lens against the word of someone who has lived with it for months.

Relying on other people's impressions

I'm not relying on "impressions". I'm relying on a more methodical approach than I am able to follow myself. The OP and subsequent admissions show why one shouldn't rely on "impressions". and why trusted sources of properly conducted tests are more reliable than the observations or "tests" conducted by amateurs.

Is this why you didn't answer gimp_dad? Again, you should quote chapter and verse if you don't want people to think you're scaremongering.

means you can't criticise the OP for not testing for these criteria.

I don't see why not having been foolish enough to think one can properly conduct a test oneself bars one from observing that somebody else hasn't conducted the tests that would provide a proper basis to make the statements OP made. One doesn't have to be a concert pianist to notice that a performance of a piano sonata left out the entire second movement.

You're saying "Prove it" while not proving your own assertions.

I have no proof to offer,

Quite, but you were criticising the OP for making sweeping statements.

other than to point to the proof made available by sources more reliable than myself or most of the other posters in this thread, including OP.

Again, it would be constructive if you pointed to the relevant bits of these sources, if you have no direct experience of the failings of this lens. As my grannie used to say, if you can't say something nice or useful, don't say anything at all.