One of the beauties of the Olympus system is that you can adapt almost any SLR lens ever made onto it via adapters (with the notable exception of Canon amongst a few others). Note Sigma have announced a Four Thirds mount version of their lens so we can have 50mm f/1.4 in AF if we really need it – although unfortunately, its still a lens designed for full frame and not specifically for Four Thirds.

Thus it is interesting to compare a few of the available 50mm lenses:

• Olympus ZD 50mm f/2.0 macro – see test here
• Sigma 50mm f/1.4 EX DG HSM – see test here
• Nikon AF-Nikkor 50mm f/1.4D – see test here
• Canon EF 50mm f/1.4 USM – see test here

When looking at the MTF charts make sure you have chosen the APS-C or DX chart for the non-Olympus lenses, and select f/2.0 for the aperture.

If you wish to use the excellent Sigma on Four Thirds, to take into account sensor size difference, the site suggests you need to multiply the MTF results by 0.87 and ignoring data past 81% of image size as this will be cropped.

Now, I use such lenses for 2 main purposes – portraiture at f/2.0 or macro at f/5.6-8.

Only the Olympus has great macro performance but that is not surprising as its the only macro lens listed there.

So let’s summarise performance for portraiture at f/2.0:

The clear winner is easily the Olympus ZD 50mm macro – it has the advantage of being designed for a smaller image circle, and it has superb performance even at f/2.0 wide open. The corners are almost as sharp as the centre and aberrations are extremely well controlled.

So if you can afford this lens, buy it – as they say on the site – no Four Thirds dSLR owner should be without it, it is that good (apart from some annoying focus issues – hopefully Olympus will make a SWD version with a focal range limiter switch and change the manual focus to that on the 50-200mm SWD, and perhaps add a magnification indicator for macro work).

The Sigma clearly outperforms the Canon and Nikon at f/2.0 – the Canon starts to get soft a third out from centre on an APS-C camera while the Nikon starts getting soft half way from centre on a DX camera. If used on a Four Thirds, the results of these would be even worse, although you crop out some of the worse performing corners at least.

What they have not tested are the manual focus legacy lenses such as the Olympus OM 50mm f/1.4, but I would expect similar results to the Canon or Nikon.

Of course, all these lenses do allow use of f/1.4 aperture which the ZD macro does not, but at a substantial cost to sharpness (use the slider on the MTF charts to see what effect different apertures have on sharpness) and aberrations as well as CA and lens flare. The OM lens certainly appears soft with substantial purple fringing on my tests when used at f/1.4 – you really need to use it at f/2.8 for reasonable results.

Bottom line – buy the Olympus ZD 50mm f/2.0 macro if you can afford it – it’s worth every bit of the money and is good enough to work well with the Olympus EC-20 2x teleconverter