Sensor and Lens Technical Specs Explained

camera lens with shallow depth of field  on a dark background

Welcome to Camera Phone Guide Part 3. If you haven’t read the other tutorials and your are a newbie to photography, I highly recommend reading Camera Phone Guide Part 1 (understanding the camera’s specs for beginners) and How to take better pictures Guide Part 2. The first two guides are for those who have non or little knowledge in the basics of photography and how to operate a mobile phone camera. This third guide is an advanced topics and here you will learn how to read and understand the phone’s camera sensor and lens technical specs.

We’ll take a closer look at the technical specs of the Samsung Galaxy S4 Zoom front-facing camera technical details. This will make it more interesting to read and learn. I am assuming that you don’t have prior knowledge and understanding of the camera and lens technical details.

Only the camera’s megapixel resolution is far from describing the camera’s performance, and many people fall into this trap due to lack of knowledge. I am here to help you out and after reading this camera phone guide, you will have much better understanding what the sensor and lens part of the specs means and what makes a camera phone like the  Samsung Galaxy S4 Zoom so unique among other phone cameras. This guide will give you knowledge that is useful for reading and understanding the sensor and lens specs of any camera, but I emphasize on mobile phone cameras, rather than burden you with details that aren’t relevant and are overkill for a single article.

We’ll start with a side by side technical camera specs comparison table, comparing the Samsung Galaxy S4 versus Galaxy S4 zoom – for both the front-facing and rear-facing cameras. This will give us a good starting point on which we will build our guide on.

 
S4
S4 Zoom
Rear-facing Camera
Sensor Resolution13.12-megapixel
13.1-megapixel (effective)

4208 x 3120 pixels (4:3)
4128 x 2322 pixels (16:9)
16.59-megapixels
16-megapixels (effective)

4608 x 3456 pixels (4:3)
4608 x 2592 pixels (16:9)
Sensor Size1/3.06" (4.69 x 3.52 mm)

1/2.33" (6.13 x 4.6 mm)

(some sources point to a 1/2.3")
Sensor Typebackside-illuminated (BSI)

model:
Sony IMX091PQ (4G Model)
Sony IMX135 (3G Model)
backside-illuminated (BSI)
ISO50 - 2000100 - 3200
Shutter Speed1/14 s - 1/10000 s16 s - 1/2000 s
Pixel Size1.12 µm (microns)1.3 4µm
Lens31m f/2.2

Largan Precision Optics

*35mm equiv.
24-240 mm f/3.1-6.3
Largan Precision Optics

*35mm equiv.
Optical Image StabilizationNo (only digital image stabilization)Yes (OIS)
Video RecordingFull HD 1080p30Full HD 1080p30 (MP4 / 17.2Mbps / Stereo)
FlashLED (3rd generation)

up to 2.4 meters
Xenon (3rd generation)

up to 6 meters
Front-facing Camera
Sensor Resolution2MP

1920 x 1088 pixels
1.9MP
Sensor Size1/6" (3.00 x 2.40 mm)1/6" (3.00 x 2.40 mm)
Sensor Typebackside-illuminated (BSI)

model: SAMSUNG S5K6B2YX03
backside-illuminated (BSI)

mode: SAMSUNG S5K6B2YX03
Pixel Size1.34 1.34 µm
Lens1.85mm f/2.4

4 Lens Elements, Plastic
1.85mm f/2.4

4 Lens Elements, Plastic
Display 5-inch Super AMOLED4.3" Super AMOLED
Weather-SealingNoNo
Focus Range7 cm - Infinity10 cm - Infinity
Dual ShotYesYes
Simultaneous HD
video and Image recording
YesYes
PanoramaYesYes
HDRYesYes

The tech spec table above shows the the differences between the cameras of the two smartphones.  In order to understand the actual differences between the two, we need to learn how to read the specs and understand what each line means. I will address the significant technical specs that are make the most significant implication on the camera’s performance and image quality. Those that photographers care for the most.

Sensor Resolution

There are many people that are sold by the camera’s resolution alone. The camera resolution is measured in megapixels. A megapixel is equal to one million pixels and can be written as ‘MP’ in short. Each of those pixels represent a single square dot in the final image that carries an RGB color value.  The higher the resolution , the bigger the image that you get.

In the specs (not always available in the official specs) you can find the sensor’s resolution. There are two type of data: the total resolution and effective resolution. The total resolution refers to the total amount of pixels on the sensor. The effective resolution refers to the amount of pixels that are actually used to produce the image, and that number is usually rounded up and present with a one decimal precision digit, so 13.57 MP can be written as 13.6 MP and some manufacturers even round it up to the nearest whole number, like 14 (MP).

The Samsung Galaxy S4 Zoom has an effective resolution of 16-megapixles. If you view the image resolution on your computer, you can see that it equals to 4608 [width] x 3456 [height] pixels. Multiply 4608 x 3456 and you get 15924248, now divide that number by million (1000000) and you get approx 15.92, and in the specs it’s rounded to 16 (MP) and this is the camera’s resolution, or better to say, the effective sensor resolution – approximately of course.

In some specs pages you can see the effective resolution for different image aspect ratios.  For the Samsung Galaxy S4 Zoom:

4608 x 3456 pixels – 4:3 aspect ratio
4608 x 2592 pixels – 16:9 aspect ratio

The aspect ratio of sensor can easily be calculated by dividing the width with the height (in pixels), and then multiply the width by a number that will give an Integer / whole number. Let me give you an example:

Calculating the Samsung Galaxy S4 Zoom sensor native aspect ratio

4608 [width] x 3456 [height] ← from the specs4608 : 3456 ← now divide the two numbers by the height (3456)
1.333333333333333 : 1 ← 1.33… is the representation of the aspect ratio as a decimal numberThe closest whole number that we can get using multiplication is 4, this is done by multiply the decimal number by 3, but we need to do that to the two numbers like so:1.333333333333333:1 x 3 ← multiplication4 : 3 ← result. This is the aspect ratio

You can apply this same formula to and sensor specs to get the aspect ratio of the sensor. Worth mentioning that some sensors have support for multiple aspect ratios. You can see that the S4 Zoom can result in images with either 4:3 or 16:9 aspect ratios. That doesn’t make the sensor a 16:9 aspect ratio. Other image aspect ratios are achieved by utilizing part of the sensor pixels instead of using all of them.

With the S4 Zoom you get 16:9 aspect ratio image because the camera will than utilize the whole width, but (3456 – 2592) 864 less pixels from the height. Some sensor do come in different aspect ratios like 3:2 for example, an aspect ratio that is widely used in DSLR cameras. A camera can therefore offer you aspect ratios like 1:1 (square), 16:9 (wide), 3:2, 4:3, and all that by utilizing different parts of the sensor pixel for the final image.

Sensor Size, Pixel Size & Pixel Density

The sensor size plays a significant role in the camera’s performance.  Two sensors can have the same resolution (e.g. 13MP) but come in different sizes. The size of the sensor is measured in inches and some vendors provides us with the height in size in millimeters. The size in inches like 1/3.06″ or 1/2.3″ doesn’t represent the diagonal length of the sensor area, but the outer diameter of the physical size of a vidicon tube sensor. The actual diagonal length is approx. two thirds of that length.

Here are the measurements for some known sensor formats and their crop factor.

Type
Diagonal (mm)
Width (mm)
Height (mm)
Crop Factor
1/10"1.601.280.9627.04
1/8"2.001.601.2021.65
1/6"3.002.401.8014.14
1/4"4.003.202.4010.81
1/3.6"5.004.003.008.65
1/3.2"5.684.543.427.61
1/3"6.004.803.607.21
1/2.7"6.725.374.046.44
1/2.5"7.185.764.296.02
1/2.3"7.666.174.555.64
1/2"8.006.404.805.41
1/1.8"8.937.185.324.84
1/1.7"9.507.605.704.55
1/1.2"13.3310.678.003.24
1"16.0012.809.602.70
35mm, full-frame43.2 - 43.33623.9 - 24.31.0

The Nokia PureView 808 uses the 1/1.2″ sensor, which measured 10.67 x 8 mm.  This is, compare to other mobile phones, a very large sensor.

Sensor size comparison, Nokia 808 PureView vs Lumia 920

Sensor size comparison, Nokia 808 PureView vs Lumia 920 (via cameraimagesensor.com)

A crop factor describes the size difference between a 35mm Full frame film or sensor and your camera’s sensor. A full frame camera like the Canon 5D Mark III, Canon EOS 6D or Nikon D800 for example (all full frame DSLR cameras) have a crop sensor of 1.0, because their sensor is a full frame sensor.

In other words, if you phone’s camera (or any other camera) has a sensor with a crop factor of 4, this means that the sensor is 4 times smaller than a full frame sensor. Furthermore, smaller sensors capture less of the projected image considering that we use the same focal length lens.  This result in an image that appears narrower, the same affect that we get when we zoom in. The crop factor helps us resolve the effective focal length of the lens and I will explain it in more details in the ‘lens’ section.

Probably the most important technical specs that you should concern about the most is the pixel size or pixel pitch. Two sensors can have the same size have pixel of different sizes. For a given size, the higher the resolution the smaller the pixels are.  We can have Sensor A that is larger than Sensor B, but Sensor A has much higher resolution than Sensor B, resulting with Sensor B actually having larger pixels, regarding its smaller size.

Pixel size is measured in microns (µm). A ‘micron’ equals to on millionth of a meter.

This can help you understand the why some cameras perform much better in low light than the others. Samsung Galaxy S4 Zoom has a pixel size of 1.3 microns, which is larger than the S4 1.12 microns. The Nokia 808 PureView pixel size is 1.4 microns, even larger. This is many times smaller compare to a pixel size of a DSLR camera. The Nikon D4 which is a Full Frame camera, each of its pixel measures 7.3 microns. This explains why DSLR cameras offer such better low light performance. Other cameras offers smaller or larger sizes, depends on the sensor size and resolution.

Another terms that you should be familiar with is called pixel density. A pixel density measured in Pixels per inch (PPI), tells us the amount of pixels per square inch can also be presented per square centimeter.  You are probably familiar with this term from display’s specs. This is very easy to calculate for sensors. You divide the sensor horizontal number of pixels by the sensor width in mm and you get the pixels/mm representation. You can than multiply that number by 25.4 (1 inch = 25.4 mm) to represent the pixel density in inches as PPI (Pixels Per linear Inch)

For example, let’s take a look how we calculated the pixel density for the Samsung Galaxy S4 Zoom

- 4608 horizontal pixels
– 6.13 mm sensor width4608 / 6.13 = 751 pixels/mmConverted to  pixel per centimeter (ppcm):751 / 10 = 75.1 pixels/cm or 75.1 ppcmConverted to pixel per inch (ppi):751 * 25.4 = 19075.4 ppi

Larger pixels result in greater dynamic range and better color accuracy.  Each pixel is actually a photodiode or photodetector. Each of these photos detectors that react to light photons. When a light photons reaches the photodiode, it excites an electron, therefore converting the converting the light to an electric charge, and this charge is than converted to a digital value using an analogue-to-digital converter or A/D.  Each pixel is than represented by an RGB value that that using a Bayer interpolation is used to constructed the final image.

Larger pixels will lead to better low light performance, allowing for each pixel to store more data / photons.

The sensor technology is also something that has direct implications on the camera’s performance.  I won’t open a whole section for that, but most of the cameras on mobile phones use a sensor technology called backside-illuminated or BSI. A BSI sensor has its wires behind the light sensitive area instead of the front compare to conventional CMOS sensors. This increase the amount of light captured and therefore improved the low-light performance of the sensor, some say up to two times in light sensitivity.

The Samsung Galaxy S4 use this BSI sensor, and most mid-range and high-end phones do.

Now you understand why more pixels can actually hurt image quality and lead to inferior light sensitivity, and result in more noise. This is why HTC has decided to go with 4MP  on its HTC One phone.

The Samsung Galaxy S4 Zoom has 16-megapixel resolution and use a 1/2.33″ BSI sensor. This is very high resolution that should have an impact on the image quality in some degree.  Many people don’t need that amount of resolution. I personally prefer having 6MP but have much better low light sensitivity, lower noise and higher dynamic range. Companies are selling us this lie for a long time and people are falling for it every time. This is why HTC took a big risk with its 4MP camera on the HTC One – not everyone understands the advantages of having a camera with 4-megapixel resolution.

Lens Focal Length and Aperture

Now that you know how to read the sensor technical specs, it’s time to move to the lens. The lens is the part of the camera that is responsible to for focusing the light onto the sensor plane.  The lens is called a ‘lens in singular, but it actually has a few lenses that when the camera focuses or zoom on a subject, one or more of those lenses actually move inside.

The most important technical specs that you should understand about the lens are focal length and aperture, but I will mention other later on.

Focal length

The Focal length the the distance in millimeters (mm) between the optical center of the a lens to the camera’s image sensor (or film) when the lens of focused at infinity.  A focal lens also tells us the angle of view and magnification. The longer the focal length (higher number), the narrower the angle of view. and the higher the magnification The shorter the focal length is, the wider the angle of view is and the smaller is the magnification.

Thumbnails of images taken with different focal lengths

Images taken with different focal lengths

Most of the camera’s on today’s smartphones are prime lenses, like the Samsung Galaxy S4 lens, and some phones come with a zoom lens, like the Samsung Galaxy S4 zoom. A prime lens is a lens with a single focal length, and it’s a non-zoom lens — you have a single field of view to shoot with it.

A zoom lens is a lens that can change the focal length, allows you to change the magnification, also referred to as “Zoom in” (higher magnification / longer focal length / narrower field of view) and “Zoom out” (smaller magnification / shorter focal length / wider field of view).

Lens with a focal length under 50 mm are referred to as ‘wide angle’ lens.  The Samsung Galaxy S4 uses  a 4.30 – 43mm f/3.1-6.3 lens for its rear-facing camera, it’s primary camera.  The part that I highlighted in red is the focal length and the part in blue is the aperture, which I will be talking about it in a a few moments.

The focal length of a prime lens has only on number. For example, the Samsung Galaxy S4 has a 31 mm f/2.2 lens, so it has only one focal length, one number as you can see, 31 mm.

A zoom lens has two numbers. The Samsung Galaxy S4 Zoom has a 4.30 – 43 mm lens. The left number is the lowest focal length of the lens, it’s widest angle (no necessarily a wide angle below 50 mm, but the widest possible on this lens), and the second number is the lens longest focal length, it’s narrowest angle (no necessarily a narrow angle, but the narrowest possible on this lens), also referred to as ‘tele-end‘.

With a zoom lens you can change the focal length from the shortest one to the longest one, choosing a focal length between those numbers, this operation is referred to as Zooming.

The lens optical zoom factor, usually written with ‘x’ after the number but some write it before it (e.g. 10x, 24x) is the difference between the longest focal length and the shorter focal length. To achieve the zoom of the lens, you divide the longest focal length number by the shortest focal length.

The Samsung Galaxy S4 Zoom primary camera has a:

43 / 4.3 = 10 ← 10x optical zoom

The Samsung Galaxy S4 has a single focal length and therefore is is said to have a 1x optical zoom and referred to as a prime lens or non-zoom lens.

What 35mm Equivalent means?

This section is very important so don’t skip it. The focal length of the Samsung Galaxy S4 zoom is 4.30 – 43 mm. This is the actual focal length of the lens. In the specs you might see it written as 24-240 mm – and yes, you are right, those are completely different numbers. The 24-240 mm is the 35mm equivalent. In photography, a 35 mm equivalent focal length indicates the angle of view of a specific combination between a lens and the camera image sensor.

If you remember, I’ve mentioned the terms crop factor earlier on, saying that a sensor with a crop factor of 4 is 4 times smaller than a 35mm full frame sensor.  The problem is with the original focal length measurement is that it doesn’t tell us what the angle of view will be because we might be using a camera with a sensor that is different than 35 mm.

Let me quote what I have written earlier:

… smaller sensors capture less of the projected image considering that we use the same focal length lens.  This result in an image that appears narrower, the same affect that we get when we zoom in. The crop factor helps us resolve the effective focal length of the lens..

So the size of the sensor has an affect on the image output, because only part of the projected light of the image actually captured on the sensor.

This means that we need to know the lens crop factor and the lens actual focal length to know the 35 mm equivalent focal length of the lens. This helps us keep track and compare the lens angle of view across many cameras that have different sensor sizes and different lenses.

The Samsung Galaxy S4 zoom lens’ focal length is 4.30 – 43 mm. The camera has a 1/2.3″ sensor with 5.58 crop factor.

How to calculate crop factor?

Given the original focal length of the lens and the 35 mm equivalent one. The crop factor is the division of either on of the 35mm equivalent focal length number to the original one. Make sure that you choose either the wide-end or tele-end number in a zoom lens (with single focal length it doesn’t matter) and divide it with its equivalent either wide-end or tele-end from the original focal length of the lens

For example, let’s calculate the crop factor of the Samsung Galaxy S4 Zoom:

240 mm (this is the 35mm equivalent) divide by 43 = 5.58 crop factor

or 24 / 4.2 = 5.58 crop factor

 

What you need to understand that we can have cameras with different sensor sizes and lenses with different focal lengths that can give us the same angle of view at the end, so we will see an image that covers that same area in front of us. OK, an example.

50 mm lens on 35mm (full frame) = 50 x 1 = 50mm ← Remember, full frame sensor has 1x crop factor
25 mm lens on Micro Four Thirds Sensor (crop factor of 2) = 25 x 2 = 50 mm ← Micro Four Thirds is a sensor that is used in Compact System Cameras

As you can see, two lenses with different focal lengths when mounted on sensors with different sizes result in the same angle of view if 39.6-degree, which is the horizontal angle of view for 50mm lens on a 35mm camera. You can check the lens horizontal angle of view using this lens angle calculator on isotton.com.

You should always search for the 35 mm focal length, because it will help you compare the lens angle of view compare to other devices, without troubling yourself knowing the crop factor of the sensor and the original focal length of the lens. Most phone manufacturers will provide you with this information, and if not, just Google it and you find it somewhere. It’s not always available in the official product page specs sheet.

The Samsung Galaxy S4 Zoom has a 24 – 240 mm (35mm equivalent) 10x optical zoom lens. Now you know what ’35mm equivalent means’ – Hooray!

Aperture

The second thing that you need to know about is the lens aperture. The aperture is a space / hole from which the light travels through.  In some cameras this opening can be controlled by the photographer (e.g. aperture priority, manual mode) and therefore allowing the photographer to have better control over the exposure. Some cameras control the aperture automatically.

Le’s take a look at the Samsung Galaxy S4 Zoom lens specs:

24 – 240 mm f/3.1-6.3

The highlighted part in red is the lens aperture. The first number 3.1 signified the maximum aperture when the lens is set to shoot at 24 mm, and the second number 6.3 is the maximum aperture when the lens is set to shoot at its longest focal length, 240 mm.

The maximum aperture tells us about the widest possible opening for a given focal length. So at 24 mm the largest opening / aperture is f/3.1 and for 240 mm the largest opening is f/6.3.  The aperture can of course be smaller than the maximum aperture.

aperture diagram

Different Aperture sizes (image credit: Cbuckley at the English language Wikipedia)

Now pay attention please:

The smaller the ƒ-number is, the larger the opening in which the light passes through is. The larger the f-number (aperture value)  is, the smaller the opening in which the light passes through is.

 

With zoom lenses the aperture changes when you zoom in (longer focal length, higher focal length number), and this is done automatically. Some lenses have a fixed aperture value like f/2.8. This means that even when you zoom in, you can still you the maximum aperture, the largest opening.  Those lenses usually are more expensive because they allow you to shoot with larger apertures even at longer focal length without resizing the aperture opening to a smaller opening.

Also a lens that has an aperture value below f/4 is referred to as a fast lens. In mobile phone, and that’s true to any lens, you should prefer having a smaller f-number / larger aperture diameter – this allows the lens to let more light to pass through it and therefore leads to better low light performance. Low light performance depends on other things rather than just the lens aperture opening. We already mentioned the pixel size and BSI sensor technology, both also help us getting better photos in low light.

f/1.4 is considered a very fast lens, because with larger apertures we can shoot at faster shutter speeds and still get a well exposed image. f/2 is a bit slower but still considered a very fast lens. the Samsung Galaxy S4 is pretty fast at the widest angle (24mm) but much slower at the tele-end (240mm).

On of the advantages that faster lenses is that the photographer can shoot at faster shutter speeds. The faster the shutter speed is, the less light that passes through. When you have a fast lens, you can shoot at faster shutter speeds and that helps to freeze fast moving subjects. For example, if you shot a car racing event with a relatively slow shutter speed of 1/60 sec for example, you probably get a blurred car, rather than a sharp image of the car when it drives through the lane.

The different between on aperture value to another is measured in f-stops.  An aperture of f/1.4 is one stop higher than f/2 and therefore said to be on stop faster. f/2.8 is said to be one stop lower than f/2 and said to be one stop slower than f/2. Opening the lens by one stop allows twice as much light to pass through.  So f/1.4 is twice faster than f/2, as the aperture opening of f/1.4 is twice the size of f/2 aperture opening.

Aperture is one of the things that affects the depth of field. Reducing the aperture size will increase the depth of field, increasing it will decrease the depth of field (DOF). The DOF calculated based in the aperture, distance from subject and focal length. The Depth of field is the distance between the nearest and farthest objects that appears in focus. Everything outside the this area will appear out of focus. This is one reason why many photographers are buying fast lenses, lenses with smaller maximum aperture, to achieve better control over the depth of field and be able to through the background out of focus while the subject or part of it is sharp.

The problem is that this is blur effect is very hard to achieve with small sensors. You usually see this effect in macro images when the camera is very close to the subject. The quality of the blur effect is referred to as Bokeh, which described the aesthetic quality of the blur.

 

Optical Image Stabilization

The Optical Image Stabilization (OIS) is a mechanism either inside the lens (lens-shift IS) or around the sensor (sensor-shift IS) that reduce the appearance of blurred images by compensating for the camera’s vertical and horizontal movements when shooting with your phone handheld (what you do probably most of the time).

Don’t be confuse with digital image stabilization. Digital image stabilization is another method that uses software technology to reduce the impact of the camera’s movement. This is used for video recording mostly and it’s done by shifting the image from one frame to the other to compensate for motion. The actual image is larger than the frame of the video, allowing the software to move the image without showing empty areas.

Another method use it elevating the ISO sensitivity when shooting stills, allowing the camera to shoot at faster shutter speeds and therefore reducing the occurrences of  blurred images. So this is more of a marketing description for automatic ISO increment, that of course leads to move noise.

The Samsung Galaxy S4 Zoom has an optical image stabilization. A necessary feature to have with a telephoto-zoom lens, especially when zooming all in and using the longest focal length. Image stabilization can also help you shoot photos at slower shutter speeds and still get a sharp image.  The Samsung Galaxy S4 Zoom has roughly 3 stops IS compensation, which means that you can shoot at shutter speeds that are 3-stops slower than what you would regularly shoot to achieve a sharp image. The Samsung Galaxy S4 (the original model) doesn’t have an optical image stabilization, only a digital image stabilization for video recording. That what makes the S4 zoom such an attractive camera for photographers.

The End

I won’t get into more technical details, but in the next guide I will provide you with much more in-depth explanation on how this actually works. This is the end of the third guide. In the forth guide I will explain how to read other relevant parts of the camera’s specs, so stay tuned.

If you find this article interesting and useful, please don’t forget to share it with others and LIKE. Thanks for reading and see you on the next guide.

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