If anything, there is no shortage of info related to Canon EOS gear on the web: the sites like DPR, Fred Miranda, POTN, to name a few, are veritable beehives of contributors sharing their own as well as popular know-how, from factual to fictional, from frivolous to speculative....questions, answers and in-betweens. Some useful in a direct way, some misleading, much of it of mild utility.
The subjective nature of image IQ assessment is compounded further in some cases by uniqueness of gear specimens, e.g., those dreaded substandard 24-70 lens copies.
Thus, one should take much of that info with a grain of salt, do a sort of plausibility/reliability test of the data before embarking on a major purchase guided by the collected reviews and tips.
One can also often find what I like to call systemic or common mode fallacies which really amount to a perpetuating sort of a myth or misguided folklore. Now, the way subjectivity enters is that while I would consider those to be "fallacies", someone else would take them for "factual descriptors"....that's the very nature of these issues.
So, in here I'd like to list a few equipment characterizations relatively well entrenched on the fora, which I consider to be myths of some sort. However, you might not. Moreover, your myth list could be different from mine.
So let us hear it !
Lastly, please try to maintain a degree of lightness and humour in your views , I do not want this to start a war of words, nor "my copy is sharper than yours and so am I" discussion type.
Petkal's Favourite Gear Forum Folklore and Myths:
(1) AF is too slow on lenses: 85L, 100 f/2.8, 180L.
(2) 180L is not very sharp for general telephoto use.
(3) Non-L lenses build and finish is inadequate.
(4) All L lenses are made of metal.
(5) The sharpest Canon lenses are 200 f/1.8 and 300 f/2.8 IS.
(6) L lenses are made to take rain and dust without any caveats.
(7) Prosumer cameras are fragile.
(8 ) The longer FL of a birding telephoto, the better.
(9) The 400 f/5.6 is the best in-flight birding lens.
(10) The 100-400 is soft at 400mm.
(11) The 100-400 pumps dust into the camera.
(12) The EF-S 17-55 f/2.8 IS USM is overpriced because it's not L.
(13) The L lenses are designed to meet a defined "L IQ standard".

..
