Lens and format size
Bob Newman ponders the future of smaller format systems and niche markets
With the release of two new full-frame mirrorless systems and Panasonic joining in with Leica’s L-mount, the aficionados of the existing, smaller format systems may wonder whether their systems are in danger of becoming obsolescent. The answer to this question is, in all probability, ‘no’. While the specialist photographic market is decreasing in size, it is unlikely to disappear. It will remain in a different form, possibly consisting of specialist niches. We have seen new niche photographic markets open up over the last few years, such as, for instance, action cameras.
The more pertinent question for any user of a camera system worried about its future is whether there is a viable niche that it will fill. The question about the mirrorless camera market is whether it consists of one niche or two, differentiated by sensor size. That question boils down to whether the difference in sensor size confers particular advantages, enough to ensure survival into the future. In general, there are two major advantages put forward favouring the use of a small sensor, which are cost and size – with the associated weight advantages. Here, we will consider the latter.
As far as camera body size is concerned, both the smaller sensor mirrorless (Micro Four Thirds and APS- C) and full frame seem to be subject to the same major constraint, the size of the human hand. In the case of the smaller examples of both, there are reported problems with usability for people with larger hands. This we might conclude that camera body size does not give a major differentiator between the systems, which leaves a consideration of the lenses.
Lens size
Lenses for the smaller formats tend to be smaller than for the full-frame cameras, but often not especially so. Sony has just released a ‘compact’ 24mm f/1.4 lens for its FE system. This lens is just a few millimetres larger than the Olympus 17mm f/1.2 lens. Clearly these lenses are different in both parameters, which poses a question as to which parameters are important with respect to this kind of comparison.
While camera markets tend to focus on sensor size, in a very real sense it is a secondary issue. A photographer really needs to be concerned about what goes into the front of the lens and the end result. A few months ago (AP 17 March 2018) I published a piece showing that depth of field can be entirely calculated in the object field (in front of the lens) from the subject distance, the angle of view and the aperture diameter. Similarly, the light energy that makes up the photo, and therefore how much noise there is (given that the major source of noise depends on the number of photons, quanta of light energy) can be determined from those two parameters plus the scene luminance. Therefore, when comparing lenses for different sized sensors, it makes sense to do so with reference to those two parameters, angle of view and aperture diameter.
To compare ‘normal lenses’, a sensible comparison would be a Micro Four Thirds 25mm f/1.4 with a full-frame 50mm f/2.8. These lenses, on the cameras for which they are designed, would yield the same angle of view and present the same aperture diameter. So, which would be larger? One other specification worth making is that the two lenses should yield similar image quality. The complexity of a well- corrected lens design increases as the f-number decreases, thus it is probable that the 25mm f/1.4 lens will be more complicated than the 50mm f/2.8. The classic designs for these are the double Gauss symmetrical design for the f/1.4 and the four- element Tessar design for the f/2.8. Thus it appears that the advantage is with the larger sensor. However, since the Micro Four Thirds lens has half the focal length, it is likely that it will extend less far from the focal plane, and this still be more compact. Even this, though, is not inevitable. The Tessar, by strengthening its front element and making the rear double negative in power becomes a ‘tele-Tessar’, with a length shorter than its focal length. Thus, it is quite feasible to make these comparable lenses comparable in size, despite the difference in sensor dimensions.