Hmm. The post here largely duplicates
@martink111's
thread for the 7.5 with the thread and the post making somewhat different statements about the lens's behaviour. So I have some questions over the accuracy and repeatability of the test procedure.
Those aside, I've recently been testing effective apertures across a set of lenses from f/5.6 to f/1.7. The two f/1.7s in the test behave exactly as expected compared to the other lenses, including an f/2.8. I've also had at various other times an f/1.4, two f/1.8s, and an f/2. Based on this data set I would say a two thirds stop difference in central area brightness would be anomalous. The Lenstip review this thread includes a
vignetting report so, if the effort here is to refer to vignetting/falloff/fourth power cosine, one can presumably expect any number from 0 to 3.3 stops just by looking at the review. Without a more precise statement of what the two thirds stop measurement in question is measuring I don't know that it's possible to disambiguate from well known behaviour of the lens.
It also depends what one means by telecentric. Formally, an image space telecentric lens has an exit pupil at infinity, a object space telecentric lens has an entrance pupil at infinity, and a bi-telecentric lens has both pupils at infinity. In any of these cases the lens's angle of view in the relevant space is therefore zero---meaning formally telecentric lenses are ultimate telephotos and cannot be wide angle by definition---and the field of view is no larger than the pupil. A corollary of the latter is field of view cannot exceed the size of the optics. The closest thing to a wide angle, object space telecentric lens is low magnification one, which is necessarily big, heavy, and expensive. See, for example, the
Thorlabs 0.051x. Optical requirements are reduced for image space telecentricity but in most photographic circumstances there's limited need for it. The beam angle reaching sensor pixels is little different between an exit pupil at infinity and one at 100-200mm.
In the weak sense of telecentricity, where it's used to suggest an (ultra)wide is designed for digital sensors by having an enhanced exit pupil distance, I would suggest this is largely a marketing claim as retrofocal designs are associated already with long exit pupil distances (
Cicala 2014b). Actual MTF increases are more likely to be associated with lens aberrations introduced to cancel aberrations created by the sensor stack, particularly for m43's comparatively thick stack (
Cicala 2014a,
Cicala 2014c), and increased use of aspheric elements in more recent designs. Potentially more relevant to this discussion, another shift in recent utlrawide design is to accept greater levels of falloff and correct them in software.
One can certainly also get substantial falloff with short exit pupil distance rangefinder/Biogon type lens designs but, from what I can tell the, m43 mount specification effectively requires rear elements be about 15+mm from the sensor. The Laowa 7.5 appears to conform to this, suggesting it's therefore necessarily a retrofocal design.
I've never used my Oly 9-18 narrower than f/5.6, but that's because I 
