My friend Josh Ginter totally knocked this one out of the park. He makes a great case for zoom lenses in general, and this one in particular:

Yet, somehow, the Olympus 12-40mm f/2.8 Pro makes next to no compromises at all. From build quality, to image quality, to ergonomics and handling, this lens is the most uncompromising lens I could have hoped for. I prepared myself mentally to be let down in numerous aspects of the lens, but every time I turn my head, I’m continually surprised with the results.

Sure, there are some compromises which can’t be overcome. The Micro 4/3 sensor physically can not produce the same depth of field as a full-frame sensor, and this can rear its head when shooting portraits with unfriendly backgrounds. Physics are physics.

But that really is the limit to the 12-40mm f/2.8 Pro’s compromises. This lens is fit and finished with professionals and enthusiasts in mind. And it delivers. It would be my absolute favourite lens if I hadn’t already picked it up its big sister, the 40-150mm f/2.8 Pro.

Josh is of course right that Micro Four Thirds cameras don’t have the same ability to blur backgrounds as Full Frame cameras, but the fact that Micro Four Thirds cameras have greater depth of field for a given F-number is not always a disadvantage.

In any situation with poor lighting conditions — concerts, interior scenes, etc. — the usual way to maintain high-enough shutter speeds to freeze movement without raising your ISO setting is to shoot at wide apertures. The problem is, on a Full Frame system and with a fast lens, shooting wide open will yield an extremely narrow depth of field, so most of the scene will be out of focus. That’s great for creating artistic effects in controlled environments, but if we’re trying to capture a group scene with plenty of movement, it may become a problem instead. The only way to keep things reasonably in focus with a Full Frame camera in these conditions is to use moderate apertures like f/5.6 and beyond.

With a Micro Four Thirds camera, on the other hand, we can shoot wide open while keeping more of the scene in focus and still enjoy all the other benefits that come with fast lenses. In this case, we could shoot at f/2.8 and gather two full stops more of light than a Full Frame camera while achieving the same depth of field. That means we can keep our ISO setting lower for longer, or use significantly higher shutter speeds, both of which could very well mean the difference between getting the shot or missing it.

This just goes to show, having greater depth of field is not always a compromise, and in fact can be one of the greatest assets of the Micro Four Thirds system in the right conditions. As ever, the important thing is to be aware of the capabilities of our tools, and use them to our advantage.

The Olympus 12-40 Pro lens is an extraordinary piece of glass in every way, and the fact that it doesn’t render the same depth of field as a Full Frame lens does not make it inherently better or worse, simply different.