With Photokina behind us and comparatively few surprises (Sigma DP1 and Fujifilm X100 were highlights for me) I thought I'd take stock and have a think about where we might go from here.
My premise is that with the new breed of mirrorless cameras we've seen the last major innovation in the large (APS to APS-C) sensor interchangeable lens camera market. There'll be refinements and new players will enter the market but no more revolutions. The problem, if you can call it that, is that
- Interchangeable lens camera bodies are already as small as they can comfortably go before holding them securely becomes an issue
and in any event
- Regardless of sensor size, if you want to achieve shallow depth of field then lens diameters can't go smaller
Here are three of my favourite mirrorless cameras, the Leica M9, Olympus E-P2 and Sony NEX-5, displayed approximately to scale:
The standout camera in terms of size is, in my personal opinion, the Leica because it's the only one to support a full-frame sensor but, of course, it's a rangefinder and doesn't do autofocus. While it is possible to argue that the space currently used by the rangefinder mechanism could be used by another manufacturer to house an electronic viewfinder (EVF) there's still a gotcha
in terms of lens size. The Leica M-series lenses are pretty compact in terms of their maximum diameters because they don't house complicated electronics and motors to drive the iris and focus mechanisms. As an example the Leica SUMMILUX-M 50 mm f/1.4 ASPH has a length of 52.5mm and a maximum diameter of 53.5mm. By comparison the Canon EF 50mm f/1.4 USM has a length of 50.5mm and a much larger maximum diameter of 73.8mm. Looking at cutaway drawings of both lenses leaves a definite impression that the Canon's extra size has nothing to do with glass.
I'll return to lens size in a moment but first there are the Olympus E-P2 and Sony NEX-5 to consider. The E-P2 was used for illustration but size wise it's pretty much the same as the Panasonic GF1 and the Samsung NX100. These are all APS-C cameras though, surprisingly perhaps, the NEX-5, with the smallest body, also sports the largest sensor (same size as that in the NX100). I'd argue that the NEX-5 probably marks an end-point in terms of miniaturisation of the body as anything smaller may be difficult to hold securely, especially with a large lens stuck on it.
So back to lens size. It's well established that the larger the sensor the shallower the depth of field is for a given f-number but, as I tried to explore in my thread Full-frame Sensors Are Better - Fact or Fiction?
, once one factors in the different focal length needed to achieve a given field of view it's a fact that Depth of Field (DoF) is, to a first approximation, determined by the diameter of the entrance pupil into the lens for a given subject. Some quick numbers can illustrate this. Using the DoF calculator here
we can see that a camera with a crop factor of 2 such as the E-P2 has a DoF of 2.42m when used with a lens of 50mm at f/2 and a subject 10m away. But with a full-framer such as the M9 we'd have to use a lens of 100mm focal length for the same field of view and to get the same DoF for a subject at 10m we would use f/4. The entrance pupil of a 50mm lens at f/2 is 25mm and, oddly enough, the entrance pupil of a 100mm lens at f/4 is also 25mm. So DoF is dependant on the size of the entrance pupil regardless of sensor size
Sorry to labour the point (especially for those of you who are already very familiar with this) but it is important in this context because it says that if you want to achieve a shallow depth of field for those artistic shots then the laws of physics dictate that lenses can't go any smaller and so, by implication, neither can the cameras they are attached to.
So we really have reached a limit now. The Sony NEX-5 is a marvel but there's absolutely no point in making a smaller interchangeable lens camera unless one is prepared to compromise artistically. Indeed if one wants a few extra knobs and dials the body could usefully be a little larger, especially if one wanted to incorporate an EVF.
That's my take on this but views differ so I'd be interested to hear what you think. Particularly if you think I've got it wrong.