Which camera sensor should you choose: Micro Four Thirds, APS-C, or full frame?

When you’re thinking about buying an advanced camera with interchangeable lenses, the question of camera sensor size quickly becomes unavoidable. Before the rise of mirrorless cameras, DSLRs dominated this category and mainly offered two sensor sizes: APS-C and full frame. Since 2008, another format has gained ground with some mirrorless cameras: Micro Four Thirds. It is a little less popular and tends to sit outside the classic APS-C/full-frame debate, but it has real advantages and definitely deserves its place in the hierarchy.

Before we go any further, let’s quickly remind ourselves what a sensor actually is. To put it simply, it is the light-sensitive surface that captures the light sent through the lens. With digital cameras, sensors brought a huge amount of flexibility: the ability to raise ISO more easily than with film, shoot both photos and video, and recover digital files directly from the camera or on a computer. A sensor is made up of photosites, which are basically light-sensitive cells and, to simplify, correspond to the number of pixels. Depending on the size of the sensor and the number of photosites, those cells will be more or less large, which has a direct impact on image quality. We’ll come back to that later in the article.

The sensor is one of the most important parts of a camera—if not the most important. It affects many characteristics of the final photo, as well as how much you can enlarge or crop an image. On that subject, you’ll also find an article on megapixels on the blog. Sensor size, price, performance, and resolution all play a role when choosing a camera. Not all sensors are equal, although sensors of the same size can usually be grouped together when they are not separated by several generations of technology. The biggest differences are mainly found between different sensor sizes. Let’s start by looking at what defines each format.

If you want to get started in photography or upgrade to a new camera, make sure you also check out our guide to the best cameras of the year!

Micro Four Thirds sensors are 17.3mm wide and 13mm high. Their particularity is that they use a 4:3 aspect ratio, a ratio also found in medium format. The width is 1.33 times the height, producing 4:3 images. This is one of the things that separates them from APS-C and full-frame sensors, which generally use a 3:2 aspect ratio.

The Micro Four Thirds standard was introduced in 2008 by Olympus and Panasonic, the two main brands behind this format. From the beginning, these brands chose to design mirrorless cameras for these sensors—in other words, cameras without a mirror or prism, and therefore without an optical viewfinder, unlike DSLRs. Today, if you are looking at a recent camera from OM System (formerly Olympus) or Panasonic’s Lumix G range, it will use this type of sensor. Panasonic’s Lumix S range, on the other hand, uses full-frame sensors.

By the way, I’ve also put together a full guide to help you choose your Micro Four Thirds lenses, depending on the kind of photography you practice.

APS-C sensors are 23.7mm wide and 15.7mm high in most brands. Canon’s APS-C sensors are slightly smaller, at 22.3mm wide and 14.9mm high. As mentioned earlier, they use a 3:2 aspect ratio, meaning the width is 1.5 times the height. They therefore use the same ratio as full-frame sensors.

The APS-C format originally existed in film and was introduced in 1996. Digital APS-C sensors are slightly smaller than the film format, which measured 25.1mm by 16.7mm. However, the film version was not especially successful, to the point that in the early days of digital photography, many people associated full frame with film and APS-C with digital. Initially offered in DSLRs by long-established brands such as Nikon, Canon, and Pentax, APS-C later expanded to Sony. Today, the format is also widely available in mirrorless cameras from Fujifilm, Canon, Leica, Sony, and Nikon through its Z DX line.

Full-frame sensors have the same dimensions as 35mm film: 36mm wide and 24mm high. This was the dominant format in the film era, and it also uses a 3:2 aspect ratio.

The 35mm format appeared at the end of the 19th century and became a photographic standard in the 1920s, when it was still known as “small format.” Some brands later adopted it in digital cameras, partly to keep using lenses designed in the previous century. Today, among interchangeable-lens cameras, full frame is one of the formats with the broadest manufacturer support, with Nikon, Canon, Pentax, Sony, Panasonic, and Leica all offering full-frame cameras. Nikon and Canon initially offered full-frame bodies mainly as DSLRs, while mirrorless systems have since made the format even more widespread.

Different sensor sizes require a little mathematical juggling to compare the field of view of lenses. Basically, a smaller sensor does not cover the entire field of view of a larger sensor. The same focal length will therefore give a different field of view depending on the sensor size. That is why we use conversions. Since calculating exact angles of view is not very practical in everyday use, we usually convert focal lengths as follows:

1. Full frame is the current reference format, so the focal lengths written on lenses are considered “real” focal lengths when used on a full-frame sensor. A 50mm lens is therefore a 50mm lens on full frame (that’s one reason people like full frame: fewer calculations to worry about, haha!),
2. APS-C has a diagonal about 1.5 times smaller than full frame (43.3/28.4 = 1.52), so you multiply the focal length by 1.5 to get the full-frame equivalent. A 50mm lens on an APS-C body therefore gives a field of view equivalent to a 75mm lens on full frame (50 × 1.5 = 75),
3. Micro Four Thirds has a diagonal about 2 times smaller than full frame (43.3/21.6 = 2), so you multiply the focal length by 2 to get the full-frame equivalent. A 50mm lens on a Micro Four Thirds sensor therefore gives a field of view equivalent to a 100mm lens on full frame (50 × 2 = 100).

In reality, these conversions are conventions, and if you have never used a full-frame sensor, they may not mean much at first. Just remember that the shorter the focal length, the wider the field of view, and vice versa. Still, it is useful to understand this equivalence because you will find plenty of articles online recommending a 50mm lens, for example. That advice mainly applies to full frame, so you need to transpose the same idea to a 35mm on APS-C or a 25mm on Micro Four Thirds. Also, don’t be fooled when you see some large-aperture lenses in the Micro Four Thirds format.

Remember: the focal length written on the lens does not change. Let’s take a 50mm lens as an example. It does not matter whether it was designed for APS-C or full frame: the focal length remains 50mm. What changes is the field of view, depending on the size of the sensor behind the lens.

Sensor size has a major influence on several aspects of an image, and the first one that often comes to mind is ISO performance. As mentioned in the introduction, photosites are larger when the sensor is larger. The larger the photosites, the better they capture light and the better the signal can be amplified. I’ll spare you the technical details, but increasing ISO mainly means amplifying the signal, and like any amplification, this also degrades it, which reduces image quality. So, the larger the sensor, the larger the photosites, and the better they generally handle that amplification. As a rough rule, to get equivalent ISO performance, you divide the value by two each time you move down one sensor size. If an image is still acceptable at ISO 6400 on a recent full-frame camera, you would generally avoid going beyond ISO 3200 on APS-C and ISO 1600 on Micro Four Thirds.

Another key aspect when choosing a sensor size is depth of field. Contrary to popular belief, a larger sensor does not directly reduce depth of field by itself. What actually happens is that, to get the same field of view with a smaller sensor, you either need to use a shorter focal length, move farther back, or combine both. That is what gives the impression that a larger sensor reduces depth of field. Even if the shortcut is not technically perfect, we can still say, in practical terms, that a larger sensor makes it easier to create shallower depth of field and stronger foreground or background blur. Here again, you can use equivalence through the aperture, the famous “f/” number. The depth of field obtained on full frame corresponds roughly to one stop wider on APS-C and two stops wider on Micro Four Thirds. So, for the same framing with an equivalent focal length—35mm on APS-C to match the field of view of 50mm on full frame, for example—if you want the same depth of field as f/2.8 on full frame, you will need to open your 35mm lens to f/2 on APS-C. On Micro Four Thirds, with a 25mm lens equivalent to 50mm full frame, you would need to open it to f/1.4. Here’s a little story to make it clearer.

Another highly sought-after aspect of a photo is sharpness. Again, a larger sensor can help you get more out of the same lens than a smaller one. Because the photosites are larger on a bigger sensor, they capture light more efficiently, and therefore preserve more of the details that make up the image. That said, it is still possible to get excellent sharpness with Micro Four Thirds, APS-C, or full frame, because sharpness also depends heavily on lens quality. Since the photosites are smaller on smaller sensors, the lens needs higher resolving power—in other words, it must be able to distinguish finer details. To get the same level of detail on APS-C as on full frame, you may therefore need a more demanding lens. This is also why high-resolution full-frame sensors are often paired with high-performance lenses. You can also apply equivalence to megapixels, but this time it is even more significant than with the diagonal because it takes the total sensor area into account. For example, a 16MP Micro Four Thirds sensor is equivalent to a 64MP full-frame sensor (16 × 4), and a 24MP APS-C sensor is equivalent to a 54MP full-frame sensor (24 × 2.25). So, if a 36MP or 50MP full-frame sensor is generally expected to be paired with very high-end lenses, this should be even more true for 24MP APS-C sensors and 16MP Micro Four Thirds sensors.

The last important aspect linked to sensor size is dynamic range. Sensors have a limited ability to reproduce a full range of light tones—from the darkest shadows to the brightest highlights—and that range is more limited than what our eyes can see. It also decreases when ISO sensitivity is raised. Although the gap has narrowed over time, a larger sensor is still generally better at delivering greater dynamic range. Color reproduction can also be better on a larger sensor, but modern sensors, including Micro Four Thirds sensors, are already so good in this area that the differences are often difficult to see in practice.

Because full frame has been a popular sensor size for such a long time, you have access to a very large number of lenses. Since many manufacturers have historically prioritized this format, that will probably remain true for years to come. Thanks to compatibility between APS-C and full frame in most systems, APS-C users can also benefit from many of these lenses. However, these lenses are designed for full frame and, as mentioned above, APS-C can be more demanding on optical quality. You may therefore get weaker results than with lenses designed specifically for APS-C, unless you buy high-end full-frame lenses.

Micro Four Thirds benefits from compatibility between OM System/Olympus and Panasonic. You can mount Olympus lenses on a Panasonic Micro Four Thirds body, and Panasonic Micro Four Thirds lenses on an Olympus or OM System body. As with APS-C, you can also adapt many full-frame lenses to current mirrorless cameras using the appropriate adapters, although I would still recommend choosing lenses designed for the sensor format whenever possible. APS-C and full frame have the advantage of existing in DSLR systems since the beginning of the digital era, with many different bodies and ranges. Mirrorless systems are newer, but their lens catalogs have grown considerably.

Still, it is not very useful to compare only body types and sensor sizes to know what your real options are. Not all full-frame cameras are DSLRs, not all mirrorless cameras are Micro Four Thirds, and not all brands offer the same range of bodies or lenses in every format. Broadly speaking, the widest historical choice in full frame is still on the Canon and Nikon DSLR side, while Fujifilm is very strong in APS-C mirrorless and Panasonic/OM System remain the main players in Micro Four Thirds. Full-frame mirrorless lens ranges have also expanded significantly and will continue to grow. On the other hand, the compatibility of full-frame lenses on APS-C bodies does not necessarily encourage Nikon, Canon, or Sony to develop as many dedicated APS-C lenses. In Micro Four Thirds, it is unlikely that many brands beyond Panasonic and OM System will push the format as strongly. This does not mean that Micro Four Thirds and APS-C are not worth considering, but depending on the format and manufacturer, your options will be more or less extensive.

For a long time, people tended to say that full frame cost much more, Fujifilm APS-C offered good value for money, and Micro Four Thirds was the format for small budgets. In reality, when you compare equivalent capabilities—especially ISO performance and depth of field—full frame is only slightly more expensive, and Micro Four Thirds is not necessarily more budget-friendly than APS-C (or even full frame, if you know where to look for good deals). Full frame has a reputation for being expensive because bodies are generally priced above $1,000, but that is mostly because manufacturers rarely make truly low-end full-frame cameras. You can look as much as you want: no full-frame mirrorless camera or DSLR is really equivalent in range to a Canon 4000D, Panasonic GX80, or Fuji X-E3.

So, once you decide to buy an interchangeable-lens camera, you should expect to spend a fairly substantial amount of money, regardless of sensor size. For entry-level cameras, Micro Four Thirds and APS-C will generally be more accessible formats simply because they offer more entry-level bodies, whereas full frame usually starts at expert or semi-pro level. When it comes to lenses, the choice can be just as interesting in full frame as in APS-C or Micro Four Thirds. Once again, it is mainly in the low-end range that you will find affordable options in APS-C and Micro Four Thirds, such as an 18-55mm f/3.5-5.6 or a 12-32mm f/3.5-5.6. We talked about it earlier, but keep focal length and aperture equivalence in mind. An 18-55mm f/3.5-5.6 on APS-C would roughly correspond to a 24-85mm f/5-8 on full frame, while a 12-32mm f/3.5-5.6 on Micro Four Thirds would correspond to a 24-64mm f/7-11—lenses that would probably be quite affordable on full frame… if they existed!

Thanks to some third-party brands, you can also find lenses in every sensor format—especially full frame—that are generally more affordable. For example, if a Panasonic 12-35mm f/2.8 costs around €850 and a Fuji 16-55mm f/2.8 around €1,000, you can also find 24-70mm f/2.8 lenses from Tamron or Sigma for Nikon/Canon DSLRs or Sony full-frame mirrorless cameras in the €1,000-1,200 range. You can even find the very good Tamron 28-75mm f/2.8 for Sony mirrorless cameras at around €750. Also keep in mind that, at these prices, you get an f/2.8 zoom in each format, but with equivalence, f/2.8 on Micro Four Thirds corresponds to f/5.6 on full frame, and f/2.8 on APS-C corresponds to f/4 on full frame. So it is not exactly the same thing.

One point that is generally true, however, is that if you do not take equivalence into account, an f/2.8 zoom for Micro Four Thirds will be smaller and lighter than its f/2.8 equivalent for APS-C, which in turn will usually be smaller and lighter than its f/2.8 equivalent for full frame. The 12-35mm, 16-55mm, and 24-70mm illustrate this difference between sensor sizes: the first weighs 300g, the second 650g, and the third 900g. This is true for many lenses, although there are exceptions, such as the recent Canon RF 70-200mm f/2.8, which weighs about 1kg, just like the Fuji 50-140mm f/2.8 for APS-C.

The explanation is simple. For the same focal length, a smaller sensor covers a narrower field of view and therefore requires a shorter focal length and a physically smaller aperture to achieve equivalent framing. That makes it possible to design lenses better suited to shorter focal lengths and smaller sensors. Using a larger-format lens on a smaller sensor—such as a full-frame lens on an APS-C body—removes this advantage, because the lens keeps the same physical dimensions whether you mount it on APS-C or full frame.

As mentioned in the budget section, Micro Four Thirds and APS-C are often more attractive for small budgets because they have more entry-level options. Once you move upmarket, the three formats become much more comparable, and you can even find interesting full-frame deals on the second-hand market. Because full frame has been so widely used, and because cameras and lenses are renewed frequently, it is often possible to find relatively recent, high-performance gear for far less than its original launch price. You can sometimes find cameras such as the Nikon D810, Canon 5DIII, or Sony A7II around €1,000, even though they cost several times more when they were released and still remain capable cameras today. Of course, this argument also applies to APS-C and Micro Four Thirds DSLR or mirrorless gear, but again, the biggest savings are usually found when choosing entry-level equipment.

The same applies to lenses. Between third-party brands and the second-hand market, you can find very good lenses at much lower prices, especially in full frame. For APS-C and Micro Four Thirds lenses, particularly in mirrorless systems, the second-hand market can be smaller because many lenses have not been renewed as often. For example, Fuji XF lenses such as the 56mm f/1.2 can be hard to find second-hand at attractive prices, even though it is an excellent lens. This is simply because there has not always been a newer high-end replacement, so many owners keep theirs. The same general idea also applies to Sony APS-C, as well as to the newer full-frame mirrorless systems from Nikon, Canon, and Panasonic, although third-party support has expanded significantly in recent years.

Still, keep in mind that entry-level interchangeable-lens cameras can remain fairly expensive and may sometimes be less interesting than an advanced compact camera, depending on your needs. In fact, I’ve written an article on this blog to help you choose a compact camera. You’ll see that, for the price, if you are not especially looking to build a full lens system, they may be more than enough for most uses, with performance and features that can rival—or even exceed—some entry-level mirrorless cameras and DSLRs.

Once again, reality is usually simpler than fantasy. You’ll find plenty of blogs and YouTube videos claiming that “you don’t need full frame,” “APS-C is enough in most cases,” or “Micro Four Thirds will disappear.” Sometimes these opinions become very strong and not very relevant, with claims like “full frame is for portraits,” “you don’t need shallow depth of field for landscapes, so full frame is useless,” and other statements suggesting that each format belongs to a specific type of photography. For the record, I once read that last comment about landscapes on a blog, only to see the same person say a few minutes later that, for landscapes, “he needed more dynamic range, so full frame was better.” Talk about saying one thing and its opposite at the same time, haha.

To put it simply, there is not really one format designed for one type of photography. In the film era, when full frame was the most common format, people shot portraits, landscapes, wildlife, and almost everything else with the same format. There is no reason you cannot do the same with APS-C or Micro Four Thirds. Basically, you do not NEED full frame, APS-C, or Micro Four Thirds. You need a camera that fits your budget, quality expectations, ergonomics, weight constraints, lens choices, and many other criteria. Sensor size is only one element—an important one, yes—but it does not create any obligation. Shooting with Micro Four Thirds does not prevent you from taking photos at night, full frame does not prevent you from doing street photography, and APS-C is not only for wildlife photography.

A larger sensor gives you better ISO performance, greater dynamic range, and shallower depth of field, but it is mostly a matter of comfort. That comfort mainly concerns image quality and the ability to create more “artistic” blur, often at the expense of compactness and lightness. It is therefore up to you to decide what level of quality you need, for what size, and within what budget. With cameras using sensors of these sizes, moving to a larger sensor is more a matter of preference, desire, and means than absolute necessity. Smaller sensors can even be an advantage for long-distance photography, such as wildlife, because focal length equivalence gives you a tighter field of view with the same focal length. A 400mm lens on full frame is often considered barely enough for wildlife, while on Micro Four Thirds it gives an 800mm “equivalent” field of view, so a much tighter frame. Full frame can also have an advantage at very short focal lengths, because designing ultra-wide lenses—such as 14mm or 20mm lenses—is complicated in every format. On full frame, they remain “true” 14mm and 20mm lenses, while on Micro Four Thirds they become equivalent to 28mm and 40mm. To get the same field of view in that format, you would need 7mm and 10mm lenses, which are even more difficult to design.

So, understand this: whatever format you choose, you are not making a mistake. Most cameras and lenses today, whether mirrorless or DSLR, are highly capable and will let you take almost any photo you dream of taking. What will really make the difference is your practice, knowledge, and experience. Moving up to a higher range or larger format brings extra comfort, but it will not revolutionize your photos by itself.

Once you’ve chosen a format, you’ll still have many other decisions to make: brand, range, grip, ergonomics, features, battery life, viewfinder quality, screen, build quality, weight, dimensions, and, finally, one equally important element: your camera lens. So don’t spend too much time wondering which format to choose. Choose one, then practice. Many techniques—such as HDR, using a flash, or simply improving your composition—will often make a bigger difference than choosing a camera with a larger sensor.

I hope this article helps you choose your camera more confidently. Remember that today’s cameras are all very capable and cover most needs, so make sure you really master your camera, whatever it is. Don’t feel frustrated or deprived because you don’t have full frame, and don’t look down on smaller formats if you do. You sometimes hear APS-C users mention the disdainful way some professional photographers look at them. In the end, that says far more about those photographers’ snobbery than about the talent of APS-C users, doesn’t it?

Good luck finding the right one for you!

See you soon,

Written by Sylvain PONS

I've been passionate about photography since 2010, learning as I went along. Today, I dedicate myself to guiding others in their choice of camera gear and sharing a variety of tips to improve their photography skills.

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