Camera Lens and Sensor Specs Explained

There are so many smartphone on the market, almost each one has its own unique camera. Let’s admit it, we all want to have the best camera. But what is exactly the best camera and what we need to look for when reading the specs? In this guide I want to answer this question in-depth by talking about two of the most important camera parts: the Sensor and the Lens. After you finish reading this guide, you’ll have a better understanding of what each spec means and what to look for when buying a new smartphone.

Intro

Mobile phone cameras have replaced the conventional compact digital camera a long time ago. Now everyone can carry a camera in his pocket, and this camera goes everywhere you go. This is a huge advantage, because the best camera is the one that you can carry with you everywhere you go. This allows you to snap pictures and record videos no matter where you are and capture moments that otherwise you wouldn’t be able to.a

The ‘Best’ camera is the one that answers the demands of the photographer. We all have different budgets, and some cameras have more limited capabilities than others.  Most people might not pay attention to the fine details, but it’s important to understand those, because once you but a specific smartphone, that camera will probably your main camera for quite some time. This is why phone manufacturers pay so much attention to the camera and do their best to improve it in each new model. People love taking and sharing photos and they don’t want the camera to limit it. For example, if you enjoy shooting at night, you want the camera to be able to capture gorgeous photos in low-light situations. Some cameras do a better job, others don’t.

So let’s start by going over the key terms and features that you should be familiar with. This will help you out making a smarter buying decision the next time you shop for a new mobile phone.

Rear vs Front Camera

Sony Xperia Z1 camera G lensYou are probably already familiar with it. Many mobile phones have two cameras, one at the rear and one at the front. Some mobile phones feature a single camera. There are several reasons why most phones feature two cameras instead of one. The main reason is it allows phone manufacturers to optimize each camera for different uses.

The rear camera usually acts as the main camera and in most phones it has the most advanced hardware components. The main camera is designed for general use (an all-purpose camera) and it replaces the need to carry an additional compact camera in your pocket.

Because of that, it usually needs more space to carry out a larger sensor and bigger lens, and the best place for it is at the back and not the front. The front needs the largest amount of space for the touchscreen. This is why in most phones you’ll find a smaller camera, which employs a smaller sensor and smaller optical complexity.

The rear camera might incorporate more advanced technologies like an optical image stabilization, more advanced AF system, an optical zoom mechanism, a bigger and stronger flash, greater lens elements to improve its optical performance — all that adds to the extra space needed to incorporate those features.

Take the Samsung Galaxy K Zoom Android smartphone for example. It features a 10x optical zoom lens at the back.

Samsung Galaxy K Zoom
Samsung Galaxy K Zoom from the side, showing its rear retractable lens extended

Of course the K Zoom is an exception, but it shows use that advanced lens optical design needs more space.

Some phone companies try to innovate in this field. For example, Oppo came up with a unique idea. Its N3 smartphone has a single motorized rotating camera. You can swivel the camera making it point to each direction and it can rotate up to 206 degrees. It brings several advantages over the conventional camera design, including the ability to shoot panoramas in up to 64-megapixels and be able to shoot very high-quality images without giving up on image quality in the front camera, because there isn’t a front camera, you can rotate it to either side.

So to sum things up. You might encounter phones with a single camera or more cameras. Some phones might have just a single camera at the back, other are more versatile. This is why it’s important to read the specs of each camera.

The Camera Image Sensor

The image sensor plays a significant role in any camera. This is the device that actually captures the light that goes through the lens. The sensor size plays a significant role in the overall camera performance and capabilities.

It is said that the larger the sensor the better the image quality. But that not always the case. Larger sensors can incorporate more advanced technologies, which might not be possible to implement those in smaller sensor due to miniaturization limitation. Sensor technologies have come a long way, and sensor manufacturers have developed new technologies to overcome some of those limitations.

One of the thing you should look at when reading the specs is what sensor technology is used, what is its maximum resolution and what is the pixel pitch (the pixel size).

Sensor Technology — there are various type of sensor technologies that have a direct effect on the image quality and the camera low-light performance.Back-illuminated sensors (BSI) are the most familiar and most used ones (compared to Front-illuminated sensors / FSI). This technology utilizes a unique sensor design that allows to increase the amount of light captured by the sensor, without getting into more complex details. This vastly improves the sensor sensitivity to light, which results in better low-light performance.

A mobile phone like the Nokia Lumia 1020 uses a BSI sensor, but uses PureView technology which has 41MP resolution. However, it is backed up with proprietary sensor and software that allows up to 3x lossles zoom at the expense of image resolution. It uses a technology called “oversampling” which reads data from seven individual pixels to form one “superpixel”. This allows the camera to have more light and color data to construct each pixel in the image. The result is an image with higher dynamic range, better color accuracy and low noise in higher ISO sensitivity.

Pixel Size — the larger the pixel, the higher the amount of photons of light that each pixel can gather. This allows the sensor to make a better translation of color data and this gives the image processor more accurate data on how to render that specific pixel. This has a direct effect on many image quality attributes. You should prefer a camera that has larger pixels, which in most cases will result in better color reproduction, improved high ISO performance, more accurate colors, higher dynamic range  and better signal-to-noise ratio.

Pixel size comparison: 1.4 microns vs 1.12 microns
Pixel relative size comparison: 1.4 microns vs 1.12 microns

HTC has chosen this path when it designed the UltraPixel camera for the HTC One M8. This lead to a vast improvement in low-light performance. The downside was that they use a 4MP 1/3″ sensor. So each pixel was relatively large (2µm pixel size), but that performance camera at the expense pf image resolution. So that was a trade-off, but for many people it was worth it.

The pixel size can be roughly calculated (if the manufacturer doesn’t provide this info) by dividing the width of the sensor in mm by the  maximum image resolution width in pixels and multiply it by 1000. This will give you roughly the size of each pixel in microns.

1/2.3-inch vs 1/1.2-inch sensor size comparison
Nokia 808 PureView sensor vs Samsung Galaxy S4 Zoom – 1/2.3-inch vs 1/1.2-inch sensor size comparison

Sensor Size — there are different type of sensor sizes. You can view a list of the popular sensor formats and sizes here on Wikipedia.  I usually search for camera with a large sensor, but as I mentioned, what you should be looking is the pixel size.  In interchangeable lens camera the sensor size would be more significant, because the lens is sold separately from the camera body and because some lenses can be mounted on both Full frame and cropped sensor cameras, this can result in change in the field of view.

That said, cameras in mobile phone come as a complete package, a lens and sensor.  So yo don’t need o mass yourself up with more information.  Although the specs are important to understand, nothing beats lab-test image quality tests.  This is what it’s recommended to read reviews and see the image quality yourself. You can also check DxOMark that do extensive tests of the camera capability under various and same testing conditions.  Each phone gets rating for both video and photo shooting. For stills DxOMark measure exposure and contrast, color, autofocus performance, texture, noise, artifacts and flash performance. In video test the exposure and contrast, color, autfocus, texture, noise, artifacts and image stabilization performance – worth a look!

I know it’s confusing to remember the sensor sizes based on their current measurement in inches, so I recommend visiting cameraimagesensor.com which shows the size in mm for each sensor with a visual comparison.

So to sum things up: pay attention to the sensor size, but more importantly, search for the sensor size in microns. This will give you an initial understanding about the camera’s performance in low-light, but don’t just count on that information and lookup some image sample and online high ISO comparison tests. Also visit dxomark.com to see how the camera stands against other phone cameras in standard lab-test.

Camera Lens / Optics

The camera lens contains glass elements with a single purpose of directing the light onto the sensor. The lens has several lens elements inside it, which some of them move forward and backwards to maintain accurate focus and to obtain a different optical zoom effect.

Most of the lenses on mobile phones don’t have optical zoom – those lenses are referred to as “prime lenses”. The reason that most phones don’t have an optical zoom is because it requires a lot of space and more advanced optical design. If companies want to keep their phone nice and slim, they can’t use a lens like that of the K Zoom. In the future we might see technologies coming to the mass market with a miniaturized optical zoom mechanism, but as of the time of writing, prime lenses are the most common ones.

This obviously makes the camera much less versatile, as you need to move closer or away from the subject in order to frame it correctly. Almost all smartphones have “Digital Zoom”. This method is used to mimic the effect of optical zoom, by digitally magnifying the image and cropping it so it matches the original size. This have a negative impact on image quality, as the image is digitally resized and samples. Whether in optical zoom, the magnification is done optically, without manipulating the original image.

“Digital zoom” can be done on your computer using a photo editing software as well. I recommend not using it. But sometimes it’s easier to zoom in using the digital zoom then editing the image later on. It saves time, especially if you don’t care that much about image quality, like when sharing images on Facebook or Twitter.

Focal Length

The lens focal length is probably the most important spec you should look for. It is measured in mm, and it signified the distance of the lens’ first element and the image sensor. There is the actual lens focal length and the equivalent focal length.

In order for you now to be confused, you should look for the equivalent focal length (in 35mm terms). The reason for that is that the equivalent focal length changes based on the sensor size and the actual lens focal length. For example, a 20mm on a full frame sensor result in 20mm, but on a APS-C sensor (which is a smaller sensor), will give you 32mm equivalent focal length.

lens horizontal angular field of view
Lens horizontal angular field of view comparison: 26mm vs 28mm

The equivalent focal length tells us the angle of view of the captured image. For example, the iPhone 6 rear camera has a 29 mm equivalent focal length. This results in ~73.4 degrees field of view, which is quite wide. In comparison, the iPhone 5S has a 31mm equivalent focal length (4.12mm actual focal length), which is equivalent to ~69.8 degrees FOV, slightly less wide than the iPhone 6 main camera.

So what all this means. A wider angle lens means that more of the scene can be fit into the image frame.  You can look at it like having less reach. The higher the focal length, the closer the subject will appear in the photo. This is one reason why in many smartphones, the front camera has a wider angle (= smaller focal length / higher field of view angle number). It is optimized for video chat and selfies. So that camera can capture you face and the surroundings instead of only showing your face filling the frame.

Wide-angle lenses cam cause distortions, but in smartphones, those are handled and fixed by software, dedicated to correct optical issues for that particular lens.

Lens Aperture

The aperture is a hole from which the light passes  through. It is measured in f-stops (e.g. f/1.8, f/5.6). The larger that opening is, the more light that can come through. The smaller the f-number, the larger that lens opening is. So f/1.8 means a larger opening than f/2.8.

To keep things simple and without getting you confused, you should prefer buying a camera with a faster aperture, or in other words, with a smaller f-number. This has a direct implication on the camera’s low-light performance, because more light can reach the sensor, and therefore more data is available for the sensor to interpolate.

Aperture diagram
Different Aperture openings with their corresponding f-number values

Furthermore, a smaller f-number for a given same sensor size, also leads to shallower depth of field effect. The blurring effect that you get when subjects in front and at the back of the main subject appears blurry. This helps to put emphasize on the subject and blurry the look of disturbing objects in the frame.

Let me give you an example.

The iPhone 6 rear camera features f/2.2 aperture. The iPhone 5 rear camera has a f/2.4 aperture. The Samsung Galaxy S6 edge has a f/1.9 aperture. So among the three, the Galaxy S6 edge has the faster aperture. The aperture signifies the largest opening possible for that particular lens. So the S6 edge lens allows more light to pass through compared to the iPhone 5 and iPhone 6.

It doesn’t means that the Samsung Galaxy S6 will have overall better low-light performance than the iPhone 6. As I mentioned, it also depends on the sensor’s pixel size and sensor performance.

Low-Light Performance

The camera low-light performance is therefore the result of having a fast aperture lens, have better quality glass and lens’ optical design, large sensor pixels and advanced sensor technology. But this is not all. Some phones use advanced image processing algorithms to allow you to shoot great images under low-light conditions.

For example, some cameras might use oversampling, offer a multiexposure shot and have more advanced noise reduction algorithms. The flash also plays a significant role and allows you to lit the subjects and get good exposure under difficult lighting conditions. But the sensor and lens specs are the most important ones to understand.

So the next time you shop for a new phone, make sure you go over those important specs and know ahead what’s in the box.

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