<disclaimer> Before you send me hate mail please note that I’m fully aware that all-else being equal larger sensors do generally provide better image quality in the form of lower noise, better dynamic range and higher resolution. My point here is that today’s m4/3 and APS-C sensors are better than the FF sensors from just a few years ago and are more than good enough for most people’s purposes. I contend that given that the quality is plenty good enough for most of us amateurs (and some pros), that other factors like bulk, weight and cost have a negative impact on our photography and our enjoyment of it, that the quality difference is mostly relevant to pixel-peepers and that expensive gear isn’t going to make anyone a better photographer. </disclaimer>
The very fact that we call 35mm-sized sensors “full-frame” (FF) implies that anything smaller is somehow less than “full”. Therefore, FF must be better and it must be something that all photographers should look up to and aspire to “upgrade” to some day. But what does FF really mean? Where did that name come from? Many who have never shot 35mm film or who were not around during the early days of digital might not understand this.
So I’ll start with a bit of history. What we call FF cameras today have sensors that are the same size as a frame of 35mm film, (135 format, i.e. 24mm x 36mm). But there was nothing “full” about the 135 format. In fact, it was the ubiquitous, affordable, small, usable film format that everyone could use, it was in fact the “lesser” film format. There was nothing special about it and photographers who wanted the best in print quality would use medium-format or even large-format cameras: 8″ x 10″ negatives, now that was full-frame! You could achieve a very shallow depth-of-field (DOF) with a medium format camera. 35mm wasn’t as good for shallow DOF but in most situations the increased DOF of the 35mm was actually an advantage! See where I’m going here? Here’s a very funny video by Zack Arias on this very subject:
So let’s go back to the 1990s, when digital photography was in its infancy. It was (and still is) very difficult to make large sensors. Sensors are complex chips and the larger the chip, the more likely it is to have defects that render it unusable (rejects). So the first digital cameras had very small sensors to keep the cost down. That was kind of OK too because as in anything else digital, smaller size is one of the main advantages people are looking for (think iPod vs Walkman, iPhone vs analog cell phones, etc.).
But as soon as sensor-sizes started approaching the size of 35mm film, the likes of Nikon and Canon started releasing DSLR cameras that could leverage their extensive catalog of 35mm lenses and this opened the digital market to the millions of photographers who had invested heavily in lenses. But since it was extremely difficult and costly to make a sensor the same size as 35mm film, these camera makers settled on a still expensive (at the time) but more feasible format called APS-C, which was based on a smaller film format that is 25.1 × 16.7 mm. The APS-C film format was used for cheap point-and-shoot cameras so no lenses existed for this format, hence the reason Canon and Nikon used their 35mm lens mounts.
But when photographers started using their 35mm lenses on APS-C cameras they noticed that the effective focal length changed and so did the angle-of-view and the DOF. This is when we started talking about the crop factor that needed to be applied (1.5 for Nikon and 1.6 for Canon) in order to tell us how a lens would really behave, but again, this is because most photographers were used to 35mm format so this became the defacto frame of reference. And from this, it was a short step to talking about “crop” sensors and later “full-frame” sensors when the first 35mm-sized sensors began to appear. But the photographers who were used to their 35mm lenses behaving a certain way were not very happy about using their lenses on “crop” sensors. This was aggravated when the pixel densities of APS-C sensors started to rise significantly and it became evident that many of their beloved 35mm lenses weren’t that sharp after all. Also, because of that 1.5x factor those beautiful wide-angle lenses they loved so much weren’t very wide at all anymore. They (myself included) started dreaming of cameras with a FF sensor so they could restore the natural order of things and they paid fortunes for them when the first ones started coming out.
To this day, Nikon, Canon and Sony Imaging (which came out of Sony’s purchase of Konica-Minolta) have not taken an APS-C system approach for their APS-C cameras. Their optical departments invest mostly in FF lenses, where the money is. They only pay lip service to the APS-C format by releasing cheap kit lenses and zooms but no serious, well built, fast primes or pro quality zooms specifically designed for APS-C. They want us to buy the more expensive FF lenses and they hope that we will upgrade from APS-C cameras to FF some day. The results of this are that while the APS-C DSLRs from Canon and Nikon and the APS-C mirrorless cameras from Sony are smaller than their FF counterparts, the lenses are not any smaller and so the size-benefit of the smaller sensors are never realized and most people don’t even think about this. Another result of this fact is that people can only see disadvantages to “crop” sensors and so they are all hoping to upgrade to FF some day.
But let’s quickly look at two systems that are completely optimized for smaller sensors.
Fujifilm came out with their X-System cameras which uses a clever X-Trans sensor that is APS-C sized. Not only are their cameras relatively small, but they have also developed an impressive array of lenses designed specifically for this format. These Fujinon XF lenses are all very high quality and about 2/3 the size, weight and cost of the FF equivalents. This allows you to build a kit that is quite a bit smaller and lighter than a FF kit and you have access to some beautiful wide-angles and many smallish primes. Because the lenses are designed for the smaller sensor and the mirrorless architecture, they can be smaller and provide excellent image performance.
The other such system is the Micro Four-Thirds system which has a sensor that is 18mm x 13.5 mm and has a “crop-factor” of 2 in relation to 35mm (FF). So a 25mm lens on the m4/3 system is equivalent to a 50mm on FF. This system is being marketed by both Olympus and Panasonic and several other brands make lenses for it. This has resulted in a system with a very wide array of lenses. The lenses are generally 1/3 to 1/2 the size of their equivalent FF lenses, creating a system that is very light and compact. They have beautiful and really high-performance zooms, superb wide-angles and incredibly small telephotos.
Now it is true that all else being equal, a larger sensor generally provides better image quality (although not always, the Fuji X-Trans sensor beats some larger sensors in terms of noise, dynamic range and colour rendering), mainly because of the larger pixels and/or higher resolutions (now up to 42 or even 50 Megapixels). However, the image quality of the m4/3 and Fuji X systems is now better than traditional 35mm film (some argue even medium-format) and it is better than the FF cameras of just 5 years ago. More importantly, the image quality is more than good enough for 99% of us. As many others have shown, a 16 Mpixel “crop” sensor is capable of easily producing high-quality large 24″ x 30″ prints, something the vast majority of us will never do. Sure if you are a pixel-peeper you will always find advantages in the larger sensors, but then why stop at 35mm format? Why not go to a medium-format? The reason is obvious, for cost and size. But I contend that the same reasoning can and should be applied to the FF systems: the disadvantage of size, weight and cost of FF systems far outweigh the image quality benefit, which you will not see at web-sized images or at the print sizes you are likely to make.
Yes, FF makes it easier to achieve shallow DOF, which is one of the main reasons people cite for going FF. But the reality is that you can quite easily achieve shallow DOF with APS-C system and even with a m4/3 system. Since the lenses are smaller and cheaper, you can buy yourself lenses with wider apertures. For example, you can buy the awesome Fujinon 56mm f/1.2 (equivalent to 85mm on FF) for about the same money as an 85mm f/1.8 and at maximum aperture the Fuji lens will give you the same DOF as the 85mm f/1.8 on a FF camera. As a bonus, that wider aperture also allows you to shoot at a lesser ISO setting, compensating for the 1-stop of noise disadvantage of the smaller sensor. I find it curious that so many photographers focus on this shallow DOF advantage of FF when the reality is that unless you are a portrait photographer, wider DOF is actually an advantage in about 80% of circumstances. Even for a portrait photographer, you don’t really want your DOF to be so shallow that the nose or even one eye is out of focus.
So by moving to a system with a smaller-sensor you can save a lot of money which you can then use to either buy more or better gear or buy yourself entry to a photo workshop, something that will truly improve your photography (hint: a FF sensor will not make you a better photographer and will most likely not result in significantly better photos). It will also result in a smaller kit that you are far more likely to carry with you. In that sense at least, you will take more and better pictures. It will also allow you to go street-shooting or nature-hiking without breaking your back and you will actually enjoy yourself more. As a bonus, you will not draw attention to yourself and not be as obvious to your street subjects and less likely to get mobbed for your gear.
I say chose a system based not on ultimate image quality, but one that has good image quality but also the size, weight, pricing and features that best suit your style of shooting. Leave the really expensive, bulky and heavy stuff to the pros. As I always say: the best camera is the one you actually have with you.