Does sensor size always matter in all situations?

Question

I recently bought a Canon SX720 camera which has the sensor size 1/2.3". It's probably the smallest sensor size. Some good camera smartphones such as Apple's 7 Plus has got 1/3" sensor. Does that mean my camera will always produce better pictures?

The benefits of a large sensor as I have noted can be:

• Better image quality in low light.
• Lower ISO required.
• Shallower depth-of-field (more background blurriness).

If I take pictures in bright light however, would the sensor size still matter i.e. bigger is always better? If that is the case it seems that my camera will always be better than any smartphone as it has a little more bigger sensor.

PS: I am not a professional photographer, just a hobbyist / aspiring student interested in photography of every day life.

Answer 1

Asking whether sensor size matters is like asking whether physics works. Of course it does.

A bigger sensor will always catch more light, require a longer lens giving lower depth of field, and will in general have higher resolution (this does not hold always, as technology improves over time). But does this mattering matter?

Remember it is not the camera who makes the picture. You do. As Ken Rockwell put it succinctly, Your Camera Doesn't Matter. Or Dorothea Lange more eloquently :

The camera is an instrument that teaches people how to see without a camera.

A lot can be done with an iPhone, or your Canon SX720. Lack of expensive gear is no excuse for crappy pictures

The implication is that you can not buy your way into better photography. Which is not necessarily a bad thing, when you think about it :)

Answer 2

I completely agree with the sentiments above - the primary difference determining the quality of the photo taken with an iPhone 7 Plus and another taken with a Canon SX720 will be the skill level, imagination, and dedication of the person pushing the button. However, there are measurable differences due to sensor size so I'll focus on those.

Let's break down the effects of a larger sensor into four categories:

1. Size of the individual photo sites on the sensor
2. Lens mechanics
3. Photographer ergonomics and other secondary effects
4. Post-procesing capabilities in-camera

Larger Photo Sites

A larger sensor will generally - although not necessarily! - have larger photosites, which means more photons are hitting the sensor for each individual pixel (in the bayer array). An APS-C camera has a diagonal which is 1/1.6th the length of a full frame sensor, which means an area which is 1/2.56th or about 0.4 of an area. Thus, we would expect a full frame sensor with the same pixel density as a APS-C crop to have 2.56x as many megapixels. So, the pixel density of a 22MP full frame sensor is roughly equivalent to an 8.6MP APS-C camera. Conversely, the full-frame equivalent to a 24MP APS-C (ex, Canon 80D) would be 61.44MP.

Obviously talking across different generations of sensors this doesn't hold true. Each generation the interstitial distances between photosites on the sensors have decreased, the base sensitivity of the sensors has increased, and the various sources of noise have decreased.

The size of the photo sensor allows, with an identical lens, more (or less) light to hit the sensor in a given amount of time. If more light is hitting a photo site then you have a more accurate representation of the brightness at that photosite; if you are getting only 10 photons hitting your photosite then if one or two do not you have a 10-20% darker photosite reading than you should; if 100 photons are hitting your photosite then if one or two do not you have a 1-2% darker photosite. At the same time, the sensor is an electronic circuit which is subject to electronic noise which can increase/decrease the reading of each of these photosites by a very small amount, which amount is the same if the "signal" is 1 as if the "signal" is 100.

These readings then get "amplified" in circuitry to the point where they can be discernable when output, so another way of saying the same thing is the more "gain" you have to apply (represented by a higher ISO rating) the more obvious the noise will be. You will "need" a higher ISO (more gain) to get a viable picture in a smaller sensor camera (or you can apply gain afterwards out of camera, but then the low-signal image is subjected to more sources of noise before it is output, so generally getting the ISO right "in camera" is key; there are some Sony sensors [Nikon bodies] which are said to be "ISO-invariant" within certain ISO ranges, which essentially means that they have controlled pipeline electronic noise introductions so well that amplifying the signal all the way in Lightroom is essentially equivalent to amplifying it in-sensor with ISO sensitivity).

Now, looking at the 20MP in 1/2.3" (Canon SX720) versus 12MP in 1/3" (Apple iPhone 7 Plus main camera). The crop factor there is 1.3x, which yields 1.7x in area. The number of pixels is 1.67x, which to my eye is vanishingly close (within the limits of measurement) identical. So, the Canon's sensor has no photosite size advantage despite being larger. It just has more pixels around the edges.

Lens Mechanics

There was an important caveat above, which is that all of that is true with an identical lens. For instance, take a Canon 5DmkIV and a Canon 80D and put any EF lens on them both, and the math around how much light gets to each photosite is absolutely true.

However, if you had a "larger" front element lens, that lens will have more "light gathering" power. This is to the square of the diameter of the front element (assuming no additional losses in-lens), so a lens 1.4x as large at the front will gather 2x the light to start transmitting down to the sensor. Think of a simple magnifying lens and lighting kindle on fire; if you have a little small magnifying glass, you might get the kindling just warm, but if your magnifying glass is larger you might get it hot enough to catch fire.

However, such a lens will also need to do much more "bending" of that light to get it projected down to the sensor size. And this is the crux of the issue: bending light introduces inefficiencies where light is lost (especially around the edges of the image circle), and the only way to combat those inefficiencies is to use more expensive lens systems with heavier elements, or to extend the length of the lens system.

If that "bending" doesn't happen perfectly, then light which should end up in one photosite instead hits another photosite, leading to poor focus.

The end result here is that with a different "lens mount" specification, you can drastically change the image quality possible with reasonably-constructed lenses. Talking specifically about phones and point-and-shoot lenses, there is no "lens mount" since they are designed for a single lens system, but the same principles apply.

Okay, all that said, you are comparing a fixed "prime" lens on an iPhone 7 to a "40x zoom" lens permanently attached to your SX720. A zoom lens almost by definition will have lower image quality than a prime lens. So, if you are trying to take an identical picture with the Canon as with the iPhone, you are likely to be disappointed because the iPhone's prime lens will likely far outshine the zoom lens zoomed out to ~20mm equivalent.

Ergonomics

A great photographer can get a great photograph with a toy camera, and a bad photographer will not get much benefit from the best camera. Good ergonomics help a photographer be better with the camera - how sturdy is it to hold the camera, how easily can the settings be manipulated with good feedback to the results, how likely are they to have the camera with them or pull it out of its bag in the first place? Ergonomics won't rescue a miserable camera nor a miserable photographer, but it can make the photographer make better use of the equipment.

Generally, the layout of buttons on a good point-and-shoot, especially a larger one like the SX720 will help the photographer a lot compared to the flat rectangle of any phone. But, with a phone's touch screen a lot more control can be more optimally organized (again, though, point-and-shoot cameras are tending towards touch screen controls in addition to basic button controls as well).

A larger sensor requires a larger lens to feed it light. Lenses are heavy. If you were talking about a DSLR, then you also have the heft and bulk of the flipping mirror, pentaprism, and lens mounting system. If you were talking about an interchangeable lens mirrorless, strike the mirror and pentaprism, but all the rest is still needed. It is a lot to carry around, so generally such systems don't get carried around except when there is known to be a need for them.

Point and shoots are obviously on a different scale than a DSLR, but given that almost all of us would scarcely imagine leaving home without our phones, the bulk of a point and shoot (and the SX720 is far from svelte) will keep you from taking it just the same as the DSLR. Doesn't mean it is a worse camera, just that it is one you can't rely on being there all the time.

Most of all, if you don't have your camera with you, the photos that day will completely suck. But, if you have multiple cameras to choose from, choose the one which gets the best results for you. When I'm going out somewhere where I expect to be taking pictures, I'll take my DSLR with me. That won't stop me, however, from whipping out my iPhone to take pictures where i didn't expect.

Finally, back to the zoom lens which I touched on above, this section is where the SX720's 40x zoom shines. You will get a much better picture of a lion with the SX720 than you are likely to survive getting with the iPhone 7 Plus. No question. Zoom lenses are popular because they allow us to take pictures much more easily, frame them far more precisely (rather than cropping after the fact, which essentially further decreases the effective sensor size), and stay alive to complete the post-processing. That is a major ergonomic win.

Post-Processing

Since you are looking at an Apple iPhone as one example, you need to take into account the very advanced logic Apple puts into its phone (and Apple is not alone here obviously, but generally the phone makers have a lot heavier reliance on post-processing computing power than any of the point-and-shoot manufacturers, because that processor is already there for them to use).

With a point-and-shoot the post-sensor electronics are generally minimal, just enough to apply the needed effects like white balance and noise reduction before outputting a JPEG image. Canon's Digic line, for instance, applies rote processing to each photo but has a primary characteristic of how quickly it can commit the image to storage (and with as little battery power consumption as possible). With an iPhone, the camera frameworks (software) are taking a lot more into account to improve your photographs. The processor is one more powerful than personal computers a decade ago, and the battery is sized to keep a large screen and wireless transmitters going for the day so processing a photograph is just a drop in that bucket. So, the iPhone can detect faces more accurately and micro-tone so that the skin tones it finds are kept natural while retaining the blues of the sky and greens of the grass, etc.

Now, this all seems nearly sacrilege to a dedicated RAW photographer - I want as little done to the sensor data as possible until I get it into Lightroom, so I can make and fine-tune those decisions to my own eye. But if you are ending up with a fully-baked JPEG anyway, a camera with a strong software processing unit and flow will generally give astoundingly better results than you would expect with the hardware being used.

tl;dr summary

They both look to be excellent cameras. I wouldn't worry about which will give you better photos in and of themselves, but if I had to choose between having one or the other, I'd choose the one I am more likely to be carrying when I need it.

Answer 3

A camera is a tool. Tools come in different shapes and sizes. Some are better suited for using one way for certain tasks. Other tools are better suited for using other ways to do other tasks.

In general larger sensors allow the possibility of better image quality, but they in no way guarantee it. Sometimes the difference in quality will be incremental and hardly even noticeable. Sometimes it will be quite obvious. Often the other things needed to allow using the larger sensor to get that quality means spending a lot more money on things such as lenses in addition to the higher initial cost of the larger sensor.

Where larger sensors have greater advantages:

• The magnification needed to view the image, as projected onto the sensor, at a specific size is smaller for a larger sensor compared to a smaller one. This means the flaws projected by the lens aren't as magnified when the image is viewed. To get the same sharpness with a smaller sensor, the lens must also be sharper.
• Since exposure is measured as the amount of light per unit area, larger sensors collect more total light for the same exposure value. This tends to make larger sensors less noisy. The age of the sensor's technology can also affect this to a significant degree. But if two sensors from the same manufacturer use the same generation of technology the larger one will almost always be less noisy when shooting the same scene with the same settings and then viewing both at the same size.
• Larger sensors tend to have larger photosites which are also known as pixel cells or sensels. Because a larger photosite has more surface area, it can collect more photons before it reaches full well capacity. This gives sensors with larger photosites more dynamic range. DR is the difference between the brightest value a sensor can record and the dimmest value that can be recorded and still be discriminated from noise. This is one reason why larger sensors are less noisy than smaller sensors.
• Since lenses of the same focal length will give a wider angle of view when used with a larger sensor, it is easier and less costly to make wide angle lenses for larger sensors.

Where smaller sensors have greater advantages:

• The magnification needed to view the image, as projected onto the sensor, at a specific size is larger for a smaller sensor compared to a larger one. This means a lens with a specific focal length will give greater "reach" with a smaller sensor than a larger sensor. Things the same distance from the camera will appear larger with a smaller sensor than on a larger one when the same focal length is used with each and the respective images are then viewed at the same display size.

• Since aperture is expressed as a ratio of the focal length to the diameter of the entrance pupil, shorter focal length lenses can achieve the same exposure or f-number with a smaller aperture diameter than a longer focal length lens. If a larger sensor needs a 100mm focal length for a certain angle of view and a smaller sensor only needs a 50mm focal length to give the same angle of view, the smaller lens can have an entrance pupil half as wide and give the same f-number as the longer lens.

• Since lenses of the same focal length will give a narrower angle of view when used with a smaller sensor, it is easier and less costly to make telephoto lenses for smaller sensors.

In the end, the quality of a tool is only as good as the skill of the one who is using the tool. Only when the tool is limiting the skill set of the user will a better tool make a difference.

Answer 4

Somehow you answered yourself.

There are specific situations where it always matters, as you pointed out.

But Photography is more about light, is more about composition, it is more about been in the right place at the right moment; the right gear helps, but it is better to have something than nothing.

If portability is also a feature, then it is better to have a small camera that not having a camera because as it was bulky it stayed at home.

Stop worrying about someone else's approval on what gear you have and go out and take pictures.

The limitations will show, but you will notice them when you are ready. Then with this experience, you will know what to do about it.