I am thinking about either buying a Nikon d3400 (APS-C or an Olympus OM-D EM-10 mkii (M4/3).
In principle I would prefer the Olympus, as it is much smaller and could fit in a jacket pocket. However I am concerned this lack of size may come at the cost of image quality due to the smaller sensor size. So how noticeable would the difference be?
I'm sure you've heard the old saying, "The best camera is the one you have with you."
Some of my favorite photos are shots I've taken with my three-year-old Samsung Galaxy Note 4, a phone with a decent camera but not a spectacular one. But it's in my pocket all the time, and when there is only a moment to grab a shot, there it is.
You can certainly get some fine shots with a Micro 4/3 camera. Here's one I like:
Pumpkin Brownie
(Olympus E-P5, Olympus 75mm f/1.8 lens, crop of JPEG straight from the camera.)
One thing I would ask yourself, especially for mountaineering, is what kinds of lenses you plan to carry. Do you plan to bring several prime lenses, or just one zoom or two? Even more than the sensor, the glass is what will make the difference.
And what's your tolerance for extra bulk and weight vs. convenience and light weight?
One nice thing with Micro 4/3 is some of the specialty lenses you can get for it that are both light and compact and inexpensive too. The Olympus 60mm macro is a real treat to use, as is the Samyang fisheye (also sold under a few other names; mine is Rokinon) that sells for less than $300.
I would even consider going a notch smaller. You can get some very nice compact cameras like the little Fujis or Sony RX100 series that fit into a tiny case and take great photos. I have an RX100M2 that I use a lot - great little camera with a not so great menu system. For example you have to dig around to get to the place down in the menu where you can aim the camera at a gray card and shoot it to set the white balance - something I do all the time.
You may want to try renting some equipment so you can really give it a good workout and see how you like it. BorrowLenses.com and LensRentals.com are a couple of reputable rental outfits (they do rent cameras as well as lenses).
A great deal here depends on when you (generally) take pictures.
In particular, with bright light, a smaller sensor makes little or no difference in quality. As the light level drops, however, a large sensor (generally) gains a greater advantage.
So, if you're mostly taking pictures of the view from a mountain top in broad daylight, chances are that the Olympus will work beautifully (and even the much smaller sensors in most cell phones will also work quite nicely).
On the other hand, if you were to take some pictures at night by the light of a camp-fire (to give only one obvious example) the differences due to sensor size will be much more noticeable--quite possibly to the point that you want to think hard about the larger sensor.
If it were up to me, I'd think hard about a mirrorless camera with an APS-C sensor. For one example, the Sony A6300 has an APS-C sensor, but is still very close to the size and weight of the Olympus (12.7 ounces vs. 12.4 ounces for the Olympus).
As a disclaimer: no, I'm not really trying to push Sony in particular--as it happens I own a Sony camera, so I'm a little more familiar with what they offer than the other brands. Canon and Nikon (for the two most obvious possibilities) offer mirrorless cameras as well. I believe the Canons use an APS-C sensor (though Canon's version of APS-C is a bit smaller than everybody else's) and the Nikons use one that's substantially smaller (even smaller than four thirds).
That does translate to smaller size and weight though--for example, the Nikon 1 series bodies are around 11 ounces apiece. If you shoot (at least primarily) in situations where a smaller sensor will work well (and given that size and weight are at an extreme premium for you), it might be worth considering something even smaller than four thirds.
In practice this is not a concern unless you have very demanding needs.
Now I would preface this by saying that my view of "image quality" is that many people, particularly beginners, tend to make the mistake of thinking of that in terms of pixel level quality or technical tests of particular parameters (like ISO performance).
In practice an "image of quality" is a result of knowing how to take a good photo. The best photos are about using light, available and artificial, using the right shutter speed and aperture, using the right focal length and framing. It's generally not about pixels - people don't look at pixels, they look at complete images.
So if you want good photos, learn the basics of technique.
But even in terms of technical capability, the gap between ASP-C and m4/3 sensors is not particularly large these days. In fact the capability of any current m4/3 sensor is better than most of the ASP-C DSLRs I have used over the years.
The m4/3 sensors are, in practice, large enough to provide good high ISO and modern ones have good dynamic range. They are not quite as good in terms of allowing very strong out of focus shooting, but in practice they are very good (and far, far better than any ordinary compact). Most beginners to large sensor systems will find the m4/3 a shock to the system in terms of having to deal with narrow depth of field as a potential issue when shooting - all that out of focus blur is a double edged sword !
And there are pros using m4/3.
I do a lot of mountaineering, and a small camera would be a big advantage.
Either system will work, but I'd edge the m4/3 if your aim is mountaineering, not because of the camera size, but because the lenses tend to be smaller on average than equivalents on the APS-C. This is because lens size scales with sensor size - bigger sensor, bigger lens. If all you ever use is a kit lens, then this is not an issue because the Sony APS-C MILCs have compact and reasonably capable small kit lenses. However for more serious work, this becomes an issue.
There is without a doubt a noticeable difference. The smaller sensor size, as you mentioned, gives a Micro Four-Thirds camera a disadvantage when it comes to low-light performance. The real question is: How much is this difference?
Let me preface this by saying that I have seen and reviewed nearly every Micro-Four Thirds cameras on the market, as well as most APS-C offerings from entry-level ones such as the D3300 to the latest D500 (plus Full-Frame DSLRs and one Medium Format System), so I know what the difference is by experience. You will find most of my reviews on my own Neocamera, although I also review for third party websites and print publications.
What I have been observing, regarding Micro Four-Thirds vs APS-C, is that the performance has been closing until about a year ago when high-end APS-C DSLR took a significant leap. This means that the difference between an Olympus OM-D E-M10 Mark II and a D3400 is less than between an E-M1 Mark II and a D500. Here is an image illustrating the point:
On the left you have the current top-of-the-line Micro Four-Thirds camera, the Olympus OM-D E-M1 Mark II, in the middle the Nikon D5500 which entry-level DSLR and, on the right, the top-of-the-line Nikon D500. As you can see, the first row is taken at ISO 200 and noise levels is very similar. The E-M1 Mark II has a tiny bit more than the others but it would not be noticeable on a typical print. The next row is taken at ISO 1600 where you can see that both the E-M1 Mark II and D5500 become visibly noisy, although you can make out details better on the D5500. On the other hand, the D500 still looks nearly impecable. The final row is taken at ISO 12800 where it is easy to see that the Olympus is way behind the rest. The D5500 got softer which is Nikon's way of hiding its noise. There is some of this on the D500 but its image remains much more usable.
There are different aspects to image-quality and certain circumstances show issues more than others such as handheld low-light photography which requires high sensitivities. When it comes to noise, the current crop of Micro Four-Thirds camera behave similarly to APS-C ones at low sensitivities, showing virtually no noise until ISO 400. As ISO is increased, both sensor sizes start adding noise but APS-C cameras really manage to keep noise low much longer. Once in a while, I do a comparison just to see where the systems are at. Here is an interesting one - although slightly outdated - pitting the Fuji X-T1 (APS-C mirrorless) against a Panasonic GH4 (Micro Four-Thirds mirrorless).
Dynamic-range is always an issue. The top-of-the-line Micro Four-Thirds cameras are still about 1 1/2 stops behind in dynamic-range compared to even older APS-C cameras. This will be a problem when shooting highly contrasting scenes.
The point is that there is a difference and a clear advantage in terms of image-quality of APS-C digital cameras but there are also great advantages to a Micro Four-Thirds camera, most notably size and weight. For the ultimate in image-quality you will need a larger sensor (even Full-Frame) but if image quality from Micro Four-Thirds cameras is good enough for your needs, you might as well consider all the advantages you are getting.
Feel free to read my review of the Olympus OM-D E-M10 Mark II and do check out its gallery. It has full-resolution images at all ISO taken right from the camera. The images will speak for themselves.
lg(0.586) = -0.77. Your calculations are in perfect agreement with Mark's.
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Commented
Jan 23, 2018 at 15:20
Since most of the answers here are kind of the general "trade-offs related to sensor area" type, I'm going to add something that I haven't seen mentioned: the difference in the aspect ratio might not be an insignificant consideration, depending on what you want to shoot. If you like the native 3:2 ratio of APS-C, because you shoot a lot of landscape or just because you like the look, you might be better served by that format, since cropping a 4:3 shot down increases the disparity in sensor size between the two systems.
On the other hand, if you like a native 4:3 ratio, maybe because you like to take a lot of portrait-oriented shots that are just too narrow in 3:2, or just like composing in something a little closer to square, it's worth noting that cropping an APS-C sensor to 4:3 decreases the difference. I've attempted to visualize this in the graphic below:
Relative dimensions of FF, APS-C 1.5/1.6, and 4/3, with aspect cropping lines.
Yes, there is a difference in image quality. If I want the ultimate quality, I don't use my m43 kit - or my DX/APS-C either, I use full frame. The m43 has slightly less dynamic range, slightly worse low light performance, slightly harsher colour, slightly less sharpness (though, in fairness, my m43 glass mostly isn't as good quality as my SLR glass).
Note the slightlys that pepper that though. And note that, even though I've got bigger chip gear, I still keep and use the m43 as well.
The best camera is the one you actually have with you. My m43 kit is smaller and lighter, and goes with me almost everywhere because of that. My SLRs come out to play when I expect to need them and don't mind hauling the weight. APS-C mirrorless is slightly smaller than an SLR kit, but not that much with lenses.
You mention mountaineering. My sport's cycling, and I'm much happier riding with m43 kit than big chip - the weight and size difference is very noticeable.
You also mention 'entry level'. In my experience, the entry level kit from all brands is now quite good enough for the likely uses anyone getting started will put it to - there are differences, sure, but they're so small as not to be worth worrying about until you start pushing the system more than you're likely to for a little while.
If it were me, I'd buy the camera I'd happily sling in a bag without thinking about it, which is the m43 (and look at the tiny Panasonic GX800 as well as the E-M10 III - it's got less physical controls so slower to use, but it's significantly smaller and lighter) - it'll get you decent results and you'll take it with you more. If you find it's a limiting factor later, you can always upgrade then with more knowledge of what you actually need from the experience.
More examples of what you can get from (now quite old) m43 and a kit lens - https://www.flickr.com/photos/gpwebb/16421348901/in/album-72157629207953363/ https://www.flickr.com/photos/gpwebb/8964546310/in/album-72157629207953363/
I have the Olympus E-M10 Mark II, and a Canon Rebel T5 (probably not exactly fair, the T5 is a bit older)
Image quality with the indoor lighting is definitely comparable.
I've tried an outdoor night shot, side by side. Olympus with my Panasonic 25mm f/1.4, Canon with the 50mm f/1.8. I tried keeping everything the same, ISO, aperture (f/1.8) and shutter speed (at around 1/50s). The Olympus turned out better with the IBIS, where as Canon didn't have IS, and it became tricky with my overcaffinated hands.
I've had other shots where I did better holding the camera steady, and there wasn't that much difference.
For certain kinds of low light shots, you could use image stacking to average out the noise. Overall, at least with the two cameras that I have, I don't find that the Canon APS-C blows the Olympus out of the water at all.
The previous answers are all good, but I'd like to add another information.
If you are interested in the finest details, always remember that the smallest detail in the sensor is limited by diffraction and the spot has the same size, in microns, of the aperture value. So if you shoot at f/2.8, the smallest detail is 2.8 microns on the sensor. This is valid with perfect lenses.
Now, smaller sensors have typically smaller pixels: my APS-C D7100 has 3.9 microns per pixel, a D750 has 6 microns and a micro 4/3 OM-DEM-10 has 3.9 microns. Medium format may have bigger pixels.
In your case both with APS-C and micro 4/3 you can "fully exploit" (theoretically!) the resolution of the sensor when shooting at f/4 or brighter. Full frames can freely shoot at f/6 without loss of details.
Of course, producing small lenses with shorter focal lengths is more difficult, so the lens could be the limiting factor on micro 4/3 compared to APS-C.
I don't think the difference would be that great, but, there are few things to consider:
Olympus has only its m4/3 system, so there's no moving from there if you ever feel the need to move to FF for instance. You'd have to switch brands. Also, Olympus has a smaller selection of accessories and lenses available for their cameras to choose from.
In my opinion Nikon is still a more versatile option as long as you don't necessarily need the compactness of a mirrorless camera. You can naturally progress to higher end bodies and you can 100% rely on the tool if you ever go pro. Don't get me wrong, I think Olympus has some nice tech, but if you're aiming for the best image quality, versatility etc., traditional DSLRs are still the way to go. One day the story will be different, but right now mirrorless is really mainly for people who need a compact body and even that isn't completely true, because as you get closer to features of a DLSR, the size and weight grows considerably. When my friend came over with his mirrorless camera to my place last year, funnily enough, my 6D with an L-lens was lighter and smaller than his Olympus...
some image quality. Go through some online photo galleries to see the example photos, but I don't think you would notice any huge difference unless you know what to look for. If you need a compact camera and you're fine with Olympus' downsides, go for it :) (Mind you this is a very opinion based question/answer and as such isn't really fit for the format of this site.)
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The area of a Nikon APS-C sensor is 384 mm2, and the area of a Micro 4/3 sensor is 225 mm2. The ratio is 1.7, which you can convert to stops with log₂ yielding about 3/4 of a stop. Not a huge amount if the sensor technologies are equal, and for modern cameras I'd assume they're extremely close. This is less than the difference between full frame and APS-C.
If you can get a 1-stop faster lens on the micro 4/3 you should be able to use half the ISO of the APS-C and find there's no IQ penalty at all.
The Nikon is a DSLR, Olympus is a mirrorless camera.
Mirrorless is far smaller and (I firmly believe) is the future. If cameras had been invented today, no-one would enineer a moving mirror.
While you focus on image quality, consider the number of shots not taken. Because you didn't carry your camera. Because is was too big.
Buy a camera that fits in your pocket, and you'll be much happier. If you want an APS-C, don't go for a DSLR but buy a Sony a6xxx. I have the Olympus myself, but the Sony is a very nice and good and popular camera - and even slightly smaller.
