Sensor Size Differences as a Wildlife Photographer

As interchangeable lens cameras have evolved, camera sensors have settled into three common sizes: Micro Four Thirds (MFT), APS-C, and Full Frame. Especially for the novice photographer, the sensor sizes can be confusing. Even for advanced photographers, not all the differences are straightforward. Since I am primarily a bird photographer, I have always wanted to do a practical comparison between these three sizes from a wildlife photographer’s perspective. I’m happy to say that my wish came true, and in this article, I will explain the differences between these three sensors from my real-world tests.

Sensor Size Overview

Micro Four Thirds

This is the smallest of the three most popular sensor sizes for wildlife photography. These sensors measure 17.4 x 13 mm. The biggest manufacturer of these cameras is OM System (formerly Olympus), while Panasonic is their main competitor.

The smaller sensor makes it possible for Micro Four Thirds cameras to be smaller. (Many of their lenses are smaller as well, but that is less true of telephotos.) Another result is that the crop sensor is, quite literally, like cropping an image from a larger camera sensor. This has pros and cons – more on this later – but for wildlife photography, it has the potential to assist with the goal of putting as many pixels as possible on a distant subject. In specific terms, Micro Four Thirds has a 2x crop factor. This means, for example, that a 400mm telephoto lens on Micro Four Thirds will match the framing of an 800mm lens on a Full Frame camera (apart from the slightly different aspect ratio of the sensors).

APS-C

These sensors can be found in cameras from most major camera companies. They are larger than Micro Four Thirds sensors and measure approximately 23 x 15 mm in size. (Canon’s APS-C sensors are a little smaller than this, and most other companies are a little larger, but the disparity is slight.)

As with MFT cameras, the biggest theoretical advantage for wildlife photographers is the smaller size and weight compared to Full Frame cameras (and potentially lower price). However, the weight advantage for APS-C is often smaller than expected, mainly because there aren’t very many dedicated APS-C supertelephoto lenses for wildlife photography. Most APS-C photographers choose to attach Full Frame lenses instead, which tend to be a little heavier.

The crop factor for APS-C cameras compared to Full Frame is about 1.5x. Again, more on that in a moment.

Full Frame

Full Frame has been with us longer than any of us can remember – well over 100 years. It began as the “35mm format” of celluloid film, and today, 36 x 24 mm Full Frame digital sensors can be found in cameras from at least nine brands. In modern photography, Full Frame has always been something of a benchmark and an established gold standard.

But is there a practical reason for the popularity of this format, or is the main reason for its widespread adoption simply inertia and adherence to tradition? The biggest arguments in favor of Full Frame are the high image quality, the control over depth of field, and the huge range of lenses and other accessories. By definition, it has no crop factor apart from 1x.

Is Bigger Always Better?

To introduce the pros and cons of each camera sensor size, it helps to do a short thought experiment. Consider three photographers, all shooting with cameras that have the same resolution and all using lenses with the same nominal focal length and aperture.

This is not just a hypothetical. For example, three well-known cameras representing these three sensor sizes – the OM System OM-1 Mark II, the Nikon D500, and the Nikon D5 – all have a resolution of about 20 megapixels. And for all three cameras, it is possible to purchase a 300mm f/4 lens (the M.Zuiko 300mm f/4.0 IS PRO for Micro Four Thirds, and the Nikon AF-S 300mm f/4E PF for both APS-C and Full Frame). What will be the differences between these systems?

First are weight and size. For these particular cameras and lenses, the weights the photographers must carry are as follows:

• Micro Four Thirds – 2074 grams (4.57 pounds)
• APS-C – 1615 grams (3.64 pounds)
• Full Frame – 2205 grams (4.86 pounds)

Interestingly, it is APS-C and not Micro Four Thirds that is lightest this time! It goes to show the importance of lens selection – the Nikon 300mm f/4 PF was designed to be as lightweight as possible, whereas the OM System 300mm f/4 PRO is a little on the heavy side. However, on average, Micro Four Thirds lenses are smaller and lighter than lenses for APS-C and Full Frame.

But more importantly, what about the photos these three photographers will get? Let’s share these cameras between three photographers and tell them to photograph the same subject with the same camera settings. Say, a bird sitting on a rock in the middle of a stream – and make sure they are the same distance away from the subject. Try to think how these three images will turn out. I will reveal after the photo.

First, the image on Micro Four Thirds will have the bird filling more of the frame. The photo is likely to have more visible noise than the photos from the other two cameras.

Second, the image on APS-C will have a little more environment around the bird. Noise will be less visible by comparison, but there most likely will still be some.

Finally, the photographer with the Full Frame camera. This time, the bird will be by far the smallest in the frame. (If it took up the entire photo on Micro Four Thirds, it will only fill 1/4th of the photo on Full Frame). There will be more environment in the photo. And the photo will have the least noise of all three photos.

What about depth of field? Well, the background will have the same level of blur in all three photos. This is because each smaller sensor’s image is like a crop from the larger sensor, and cropping does not change depth of field.

And what if the photographer with the Full Frame camera decided to crop the image to look the same as the APS-C or Micro Four Thirds photo? It would be possible, but at the expense of losing a lot of pixels! The images would look mostly the same, but cropping to an APS-C level would reduce the resolution from 20 megapixels to about 8.5 megapixels, and cropping to a Micro Four Thirds level would reduce the resolution to about 5 megapixels.

What is the lesson here? With the same sensor resolution, focal length, and distance from the subject, the photo with Micro Four Thirds will place the highest number of pixels on the subject (resulting in the most detail). So much for the larger camera sensor always being better!

In practice, the situation would probably be somewhat different. For example, most Full Frame cameras nowadays have more than 20 megapixels. If you shoot with a 45 megapixel Nikon D850 or Nikon Z8, then you can do some serious cropping and still keep a lot of resolution. Even more so with a 60+ megapixel Full Frame camera like the Sony a7R V. The highest resolution APS-C camera has about 40 megapixels, while the highest resolution Micro Four Thirds cameras has about 25 megapixels.

Also, photographers tend to stand wherever is needed to take their photos. Stand closer with Full Frame, or farther back with Micro Four Thirds, and you can get whatever framing you want. The photographer with the OM-1 (Micro Four Thirds) would probably be several meters back from the photographer with the Nikon D5 (Full Frame). Or perhaps the Full Frame photographer would use a longer lens, like a 600mm, to match the desired composition.

As soon as you introduce different lenses and different camera-to-subject distances, other variables arise between the different sensor sizes. For example, getting closer to your subject results in a shallower depth of field. So does using a longer focal length lens. As a result, if two photos have the same framing despite different camera sensors, the larger sensor will have less depth of field. (This assumes all camera settings are kept identical across cameras, and no cropping is done to match the compositions.)

In fact, you can use the crop factor to find both the equivalent focal length and the equivalent depth of field between two camera sensors. Want to match a Micro Four Thirds camera with a 300mm f/4 lens, and you have a Full Frame camera? Recall that there is a 2x crop factor between these systems. So, as long as you don’t move forward or backward, you can shoot with a 600mm lens at f/8 on Full Frame to get a comparable framing and depth of field.

An important practical difference is which lenses are available for which systems. In theory, it is nice that you could always match the composition and depth of field between two systems – just multiply or divide by the crop factor. But camera companies only make so many lenses. A 200mm f/2 lens on Full Frame could only be matched by a (nonexistent) 100mm f/1.0 lens on Micro Four Thirds, for example.

Generally speaking, Micro Four Thirds offers more choice for lighter-weight supertelephoto lenses. Full Frame offers more telephotos with shallow depth of field and bright apertures. (APS-C photographers usually just use Full Frame lenses, except for Fuji shooters who have more dedicated APS-C options.)

However, “generally speaking” only matters if you’re still not sure which lens to buy. Every company makes some unique lenses. And if you don’t like the native options, it may be possible to adapt a lens or find a third-party lens that suits your needs. You may also be able to use a teleconverter to change the focal length and maximum aperture of a lens, such as turning a 400mm f/2.8 lens into an 800mm f/5.6 with a 2x teleconverter.

Now, what about image quality?

It is true that larger sensors have an advantage here. Especially if we go back to the example of three 20-megapixel cameras, and then imagine shooting all three at a high ISO value and cropping or doing heavy post-processing to the images. The Full Frame photo will be cleaner than the APS-C photo, which will be cleaner than the Micro Four Thirds photo.

However, the image quality advantages to Full Frame go away if you need to crop the photo extensively. If you crop it to match the field of view of an APS-C camera, you will get APS-C image quality (or a little better or worse, depending on how much resolution you started with, and on individual camera sensor differences). And cropping to a Micro Four Thirds field of view gets you Micro Four Thirds image quality at best (in reality, most likely worse, because there are no 80 megapixel Full Frame cameras that would allow you to retain 20 megapixels after cropping so extensively).

Since wildlife photographers often crop their photos, this is a big argument in favor of smaller camera sensors. If you were already going to crop your Full Frame photos so much, then you could have simply used lighter, less expensive equipment and gotten the same results.

In fact, the biggest image quality advantages of Full Frame only occur if you’re prepared to limit how much you crop! And unless you’re mainly shooting animalscapes, this often means a longer focal length lens will be necessary on Full Frame, potentially in combination with getting closer to your subject. This results in a higher expense and a heavier kit, and sometimes a higher chance of scaring away your subject.

Ultimately, Full Frame does have some clear advantages – but you often need to pay more, and you definitely need to optimize your techniques, or you won’t see them. Given that smaller camera sensors still are capable of great image quality, you can see why APS-C and Micro Four Thirds remain popular for wildlife photography.

Small Sensor, Big Noise?

I’ve explained how larger camera sensors have the potential for better image quality. If you don’t crop your images, and you use the same camera settings, the improvements are (very roughly) one stop of noise performance for APS-C over Micro Four Thirds, and one additional stop of noise performance for Full Frame over APS-C. All else equal – which it may not be, depending on the noise performance of each individual camera sensor – a photo at ISO 1600 on Micro Four Thirds will have similar noise as a photo at ISO 6400 on Full Frame (representing two stops of difference: ISO 1600 to ISO 3200 to ISO 6400).

However, noise reduction software has improved greatly over the years. It allows us to use ridiculously high ISOs without dramatically reducing the quality of the photos. So even though larger sensors have a clear advantage in low light on paper, post-processing can make most images taken in reasonable light look good (as well as many images taken in unreasonable light)!

Even with Micro Four Thirds, I found myself able to use ISOs around 5000-6400 and sometimes higher, if the subject required it. And these weren’t “break glass in case of emergency” ISO values; I used them regularly and without fear, knowing that it would be possible to reduce the most objectionable noise in post-processing.

So yes, the advantages still persist (about one stop better noise performance as you jump from Micro Four Thirds to APS-C, and roughly one additional stop when you jump to Full Frame). But if you’re able to stick to ISO 6400 and lower, then you can convincingly get away with any of these three sensor sizes today.

Is the Micro Four Thirds System Lighter?

For most photographers, the immediate answer to this question is “yes, of course.” But is it really the case?

I have hinted at this question already, when I showed that the Micro Four Thirds kit with the OM System 300mm f/4 was heavier than the APS-C kit with the Nikon 300mm f/4 PF. Now, I can find plenty of examples where the Micro Four Thirds kit comes out ahead. But most of the obvious benefits of Micro Four Thirds for size and weight occur with non-telephoto lenses, like a wide-angle or normal prime lens.

The unfortunate fact is that, if your main photographic interest is wildlife, your back and shoulders will suffer similarly, regardless of sensor size. This is because a good supertelephoto lens is often many times heavier than the camera it is attached to. A long focal length with a bright maximum aperture – considered ideal for wildlife photography – is always going to be heavy.

Remember that if you want the same framing and depth of field between camera systems, you need to multiply both the focal length and the maximum aperture by the crop factor. A (hypothetical) 400mm f/5.6 lens on APS-C may be super light and seem like a great choice, but multiply that by the crop factor of 1.5, and you see that you can match it with something like a 600mm f/8.4 on Full Frame. Something like Canon’s 600mm f/8 would be close enough, and that lens is already nice and light, so the hypothetical 400mm f/5.6 on APS-C might not be as appealing as you first thought!

I am still inclined to say that the answer to this question – “Is the Micro Four Thirds system lighter?” – is yes. However, it is a very conditional answer that depends much more on the specific camera and lens you choose.

(For the record, I would say the same thing about mirrorless versus DSLR. Speaking as someone who uses an adapted 500mm f/4 F-mount lens on my Nikon Z9, I am quite confident that my mirrorless kit is heavier than my old DSLR kit!)

Conclusion

I spent three beautiful mornings photographing the White-throated Dipper family, during which I had the opportunity to observe and photograph these exceptional birds (by the way, there are only five species of dippers in the whole world). The pair I photographed had built their nest in one of Prague’s parks, in an unusually busy spot, under a boulder next to a stream. As a result, they were accustomed to human presence and paid no attention to the fact that I was sitting in “their” stream for long hours.

This allowed me to shoot them with not one, or even three cameras, but four. I had two Full Frame cameras (Nikon D850 and Z9), one APS-C model (Nikon D500), and even probably the best Micro Four Thirds combo for wildlife, the OM System OM-1 Mark II with a 150-400mm f/4.5 lens. My goal was to try three different systems on the same subject so that you could compare how the different sensor sizes would affect the resulting photos.

My goal wasn’t to pick a winner, as every photographer has their own specific needs. In fact, my main feeling is that it’s really hard to make a bad choice these days. Regardless of sensor size, all four of the cameras were capable of taking great, detailed photos. With careful processing, even the dreaded Achilles heel of small sensors – noise at high ISOs – was not a substantial problem.

If I had to name one practical benefit of Full Frame, it may not be one that you would expect. My answer isn’t the high ISO performance or even the wider range of lens options. What I found the most beneficial was the greater freedom in cropping photos in post-processing. Yes, I already discussed how too much cropping on Full Frame negates the benefits, and that’s true – but cropping too much on APS-C or Micro Four Thirds is worse. Rather than simply negating the benefits, you could end up with an unusable image if you try to crop too far.

This, however, is something that can be overcome with good technique and discipline in the first place. It simply means that you need to frame your subjects more carefully on smaller sensors so as not to require extensive cropping in post-processing. Perhaps this is even a benefit in the long run; a Full Frame camera lets you be a little lazy with your framing, and that can hurt your photography skills.

It reminded me how much more important it is to know your camera and set it correctly than to chase after a particular sensor size, or even to chase after a particular lens.

A Final Exercise

At the very end, I have 10 sample photos taken with three different sensor sizes. Can you tell them apart?

I hope you enjoyed this article! Camera sensor sizes and equivalence can be controversial topics, so I request that if you leave a comment, let us be civil and remember that there is no reason to talk badly about a photographer’s choice of gear.