I'm not sure what you mean by "ad driven tabloid". Do you mean the DxO website? That's where I got my information about their scores.
Okay, so you raise an interesting question about burden of proof. Who has the burden of proof? As a *general* principle, it is with the person making the claim. If someone claims that DxO marks are meaningless, that is a claim and they shoulder a burden of proof for that claim. So there is nothing wrong with me asking people for evidence for such claims - i'm placing a burden of proof on the shoulders of those who make that claim. As I'll argue below, this general principle, however, cannot be extended universally, on pain of radical skepticism.
What burden of proof do *I* have? *At most*, I have a burden to provide reasons for only those claims that I have made. Me asking those who have claimed, for example, that DxO marks carry no information, for grounds for their claim, does not result in any burden of proof for me to establish anything.
But I have made some claims. My first claim was that DxO gave the scores that I said they do. I could provide you with links, but I'm going to assume that that is not your concern. I think what you are asking for evidence for is for my assumption, later made explicit, that DxO marks carry some information (and are therefore not meaningless). Here is my response:
All reasoned argument has to start somewhere with premises (not always explicitly stated, of course) that are not ultimately subjected to further questioning. (In order to get anywhere in an argument, you have to start somewhere.) If you express a belief I *could* ask you for a reason for that belief, then a reason for your reason, and then a reason for your reason for your reason, and so on ad infinitum. The result of demanding that reasons be provided for *any and all* beliefs is to demand something that *cannot* be given and leads to radical philosophical skepticism. (Which is bad!)
Our premises almost always include someone saying something (something on the internet, in a newspaper, on tv, on the news, in Pentaxforums, in a peer-reviewed scientific paper, etc.) The vast majority of the things that we humans believe are based ultimately on the testimony of others, and that requires a large degree of *trust*. Without trust there is almost nothing we could learn about the world. For example, I believe that gold atoms have 79 protons in its nucleus. I believe that only because lots of sources that I trust have said that. I haven't got any personal experience that corroborates that, and neither have even the vast majority of scientists. I certainly have not experimentally tested it. This does not make our beliefs irrational however, for reasons that I'll try to make clear.
The challenge lies in deciding where to place our trust.
In the case of lenses, people here have pointed to, for example, Lensrentals as a source of information about lenses or to MTF charts sourced on the internet. To use those as sources of information requires some trust. One could equally ask the same question there: where is your evidence that Lensrentals actually carried out the tests they say that they did? Where is your evidence that, even if they did carry out those tests, that their instruments work or are well-calibrated? Etc. If one were to adopt such a radical skeptical approach then no one has any reason for anything if it is based on the testimony of someone else - which almost all of what we believe about the world is. I take that kind of radical skeptical approach to be coherent, but also very corrosive for the general enterprise of critical enquiry. In other words, I take it that at some level we have to trust others if we are to have informed opinions - as we desperately need to have - that extend beyond our own immediate and very narrow personal experience.
So I believe that the *default* should be that a speaker sincerely expressing a declarative statement raises the probability of the statement being true. In the absence of grounds for thinking that the statement is either a) false, or b) without epistemic warrant (i.e., without rational justification), it is then reasonable to believe that the person's statement carries information. This is *not* to say that the statement is true - it is simply to say that it raises the probability of the statement being true. (This is related to what is sometimes called the principle of credulity, or principle of epistemic charity.) Very roughly speaking, without getting into to much detail, we should give epistemic credit to testimony *unless* we have grounds to think that the testifier is lying, stupid, or ill-informed. Without that principle we could not learn anything from anyone giving testimony. Since I think we *can* and *do* learn things from testimony, I endorse that principle. I think pretty much everyone does, implicitly.
So far, I have no reason to think DxO are lying, no reason to think that they are stupid, and no reason to think that they are ill-informed, when they make statements about, say, the sharpness of the lenses they test. The same goes for Lensrentals, or ePhotozine, or Optical Limits or Lenstips, etc. I therefore give them epistemic credit and treat their statements as carrying some information. There are, of course, many factors that modulate the reasonableness of crediting their statements with carrying information, and many factors that modulate the amount of information their testimony is likely to carry (such as the number of lenses they say they test), and I strive to take those factors into account.
For analogy, suppose I want to know what the time is and I ask someone and they say: "it's nearly ten". I take it that I now have some reason to believe that it is nearly ten. It may well be that there are better and more accurate sources of information about the time out there, but it would be unreasonable for someone to simply *assume* that the statement carried *no* information about the time without some reason to do with, say, the person's poor sight, their high alcohol levels, their propensity to lie, the recent operational failures of their watch, etc. In other words, they would need some reason if their dismissal of the statement is to be reasonable.
None of this means that DxO marks *are* worth anything. BUT, it does mean that if someone claims that they are not worth anything, then it is reasonable *for me* to ask for the reasons for thinking that.
---------- Post added 08-27-19 at 02:18 AM ----------
Then the test would be worthless. I could equally ask: What if the apparatus LensRentals used was badly calibrated? Then their tests would be useless. How do such possibilities show that the DxO mark should be ignored? Have you grounds to believe that it was not in focus? Have you reason to think that DxO folks don't know how to focus a lens properly? I have no such reason to think such things.
 Quote: A real test like the camera companies or Roger Cicala does is in a rig just for the lens: Lens Rentals | Blog
Otherwise you're not testing the lens, you're testing that individual copy of the lens, the camera body, the software algorithm, the subject setup and lighting, and the skill of the individual photographer. It's called controlling variables. You are testing the lens, but you are not testing *just* the lens. That is, differences in the lens makes a difference to the marks, but it is not the only thing that makes a difference. Claiming, with justification in my view, that Lensrentals is a *better* source of lens information than DxO marks is something I would certainly agree with. But it does absolutely nothing to show that DxO marks should be ignored. All you are saying is that there are other factors that we need to control for before interpreting the marks from any source as a measure of the lens' properties.
Right. And again, none of that shows that the DxO marks carry no information or should be ignored. Have you any reason to think that the DxO testing also used a decentred lens? Could they have? Sure!
Yep, and again....
What you possibly can tell me concerns your experiences of your particular copies of those lenses. Your testimony carries information, but it does nothing to show that DxO marks should be ignored, rather than, say, showing that Pentax lenses vary in their sharpness from one copy of a lens to another.
I love that Pentax lens as well. And those are some good reasons to prefer the Pentax lens over the Sony, imo, all else being equal. What they are not are reasons to dismiss or ignore DxO marks. That there is a lot more to deciding which lens will be best for oneself than DxO marks (or MTF charts, for that matter) is not something I have remotely disagreed with.
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