It's a 300mm F4 that takes pictures like a 600mm F8 on FF. Toss on a 1.4TC and you're at 840mm F11.2.
If you want to go that route, get one of those cheap Canon F11 800mm lenses and be done with it. It's lighter and less than a third of the price of the Olympus option, while offering you greater room to grow with bodies and lenses.
High-end (read: expensive) M43 only looks like a good choice if you're stubborn and ignore math.
Silly comment. Based on a very strange criteria of logic of cheaper lens = identical results
The 'logic' in place here has been that the cheaper Olympus 300/4 produces identical results to the much more expensive Nikon, Canon and Sony 600/4 lenses. It clearly doesn't. On the other hand it's very likely indeed that the Canon 800/11 will produce better results on a Canon R camera than the Olympus 300 f/4 with a 1.4x TC will on an Olympus camera. For a start, the Canon lens is cheap for a whole range of reasons other than optical. It doesn't have an aperture diaphragm, for instance, and it's pretty much all plastic, but that hasn't a lot to do with the optical performance.
The ePHOTOzine review of the Canon shows it to yield just shy of 3000 lw/ph at it's only stop of f/11. The same reviewers
review of the Olympus 300/4 shows that at f/4 it gives about 2750 lw/ph, and that will be reduced by the TC. So I think that it's clear that the results, if not identical, will give the advantage to the Canon, cheap though it is.
The new Nikon Z 800/6.3 is only about twice as expensive as the Olympus, and that gives an extra 1000 lw/ph,
according to this reviewer . Its peak is at f/8 and it is already diffraction limited at f/11, giving just over 3500 lw/ph.
