[thxbb12]

Of course it isn't. The size of the hole is the same as with a FF 600mm f8. The cone of light gathered is the same too. So how can it gather more light?

 

f/4 on MFT meters the same as f/4 on FF. Similarly an f/4 lens on APS-C or medium format would meter the same. The sensor size is irrelevant.

Relative to the sensor size, the amount of light hitting the MFT sensor is the same as a f/4 would be on FF. Consequently, the exposure time is similar.

This is what I meant to say.

 

What really matters is that a 300mm f/4 MFT lens acts as a 600mm f/4 FF equivalent lens in terms of exposure and f/8 in terms of DOF. That makes it for a hand hold-able system which is not the case when considering FF.