By popular request, well a couple of people asked, I thought I would attempt to answer a question that I quite often see discussed online that is “How much better is the image quality from the Olympus M Zuiko 300mm f/4 Pro than the Olympus M Zuiko 4-150mm f/2.8 Pro with the MC20 2x teleconverter ?”
The 40-150 f/2.8 Pro is, I think, one of the best loved of Olympus lenses and rightly so because it covers a very useful range, is fast at f/2.8 right through the focal range and is sharp.
For me there are three downsides to this lens which I live in hope that Olympus will remedy with a second version.
The first is that the lens does not have OIS, now whilst this is not a massive issue when the lens is used bare because of the fantastic IBIS on the Olympus cameras it does become an issue when you put the MC20 on the lens. As a general rule the longer the focal length the less capable IBIS becomes and the greater the need for OIS takes over, better still to have both and this of course is where the 300mm F/4 Pro really scores in my opinion.
Leaving image quality aside if you want to shoot alot of images at 300mm or longer (with the MC14 or MC20) in my opinion, if the budget will stretch, the 300mm is worth getting just because of the image stabilisation. With the 300mm I can hand hold down to shutter speeds as low as 1/20 of a second and whilst you cannot always do this because of subject movement what it does allow you to do is to keep the iso as low as you can which of course on any m43 camera is always the best way to acheive the highest possible image quality.
The second downside to the 40-150, for me, is that the lens foot is not arca swiss compatible meaning I have to attach an additional plate, not a huge issue but they can work loose and frankly its just a pain when compared with the 300 where the lens foot is arca swiss compatible.
The third downside, and a well known issue with this lens, is the lens hood. It is far too complex and may as well be made of cheese for how robust it is, I really don’t know what Olympus were thinking when they designed it ! Again the 300 doesn’t suffer with this problem.
All that said the 300 cannot of course replace the 40-150. The 40-150 is a great lens and an ideal focal length range for certain tasks, for safari for example, where when photographing bigger mammals the ability to zoom is essential.
So the question I am trying to answer here is simply, if you want to shoot at 300mm (600mm FF equivalent) is it worth getting the 300mm in addition to the 40-150mm ? or can you “make do” with using the MC20 ?
So all that said lets take a look at what really matters the image quality of these two options.
So adopting the same methodology as in my test of the MC teleconverters here are my results.
NB: images are unsharpened RAW and click to view larger.
Firsly here is the full 300mm image so that you can see the extent to which the susequent images have been cropped. As an aside the the 40-150mm plus MC20 gives an image that is slightly wider than the 300mm, perthaps more like 290mm.
Here is the Olympus 300m bare lens (Full Frame equivalent 600mm) wide open at f/4, heavy crop
Next we have the 40-150mm @ 150mm with the MC20 wide open i.e f/5.6 – as expected there is no contest really, the 300mm clearly shows more detail and is noticably sharper.
Does stopping the 40-150mm plus MC 20 combination dow make any difference ? – well here is that combo stopped down one stop to f/8 and yes it does improve things quite a bit, still not as good as the 300mm bare but much better than wide open.
Conclusion – It is no surprise to me that the 300mm outperforms the 4-150mm plus MC20 combo, there was never any doubt that would be the case, a prime against a zoom with a teleconveter is always going to be a non contest really. For me the 40-150mm plus MC20 combo is too soft wide open, for bird photography sharpness is absolutely key else feather detail is lost and stopping down is just not an option since that almost inevitably entails using a higher iso which is far more impactful on image quality than the gains from stopping down.
As always my views are based on my copy of the lenses and for my type of photography – your mileage may well vary.
A Good Place to Stand 
I agree with your findings. I have both lenses and both the MC-14 and MC-20 TCs. The 40-150 and MC-20 makes a hellishly easy package to haul along for general shooting, though.
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A very good comparison, I have 40-150mm lens but thinking of buying 300 mm f4 for bird photography and it has helped me to go ahead and buy it, although it may be heavier.
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