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part II: comparison of sensors, pixel density and area of \u200b\u200bphotosite

In the previous post, see Sensors I , learn or review the following:
(one recommended having read the previous post for a better understanding of this)

.- recall the factors that involved in the quality of a photo.
.- Sensor describe the camera.
.- learned the meaning of Signal and Noise .
.- learned what the Signal to Noise .
.- remember how to set the ISO value .
.- learned what are the photosites.
.- We saw how it relates to the size of the photosites with signal to noise ratio.
.- We could see how it affects the ISO in some photos taken with a camera (point & shoot) small sensor, generating a tremendous amount of noise at high ISO values.
.- We learned that if we have sensors of the same resolution, size if it influences the quality, it has, the larger sensors, larger photosites (yellow graph).
.- We saw how, if a sensor of a given size will increase the resolution, the photosites should, logically, be smaller in order to put more items in the same area (blue graph).
.- not necessarily learned that a larger sensor always mean quality.

Well, industrially manufactured sensors of different sizes and for different uses, but basically we're going to have to deal with some of them, how such as "Full Frame" (full), APS C, (one of the most common sizes in DSLR cameras), or Four Thirds 4 / 3 (used by Olympus and Panasonic), and a couple of sizes used in cameras Point & Shoot and Brige Cameras (also called Prosumer).

Full Frame sensors have the same area as the film of 35 mm (36 x 24 mm.) And this size is against all comparisons are made and equivalents, especially to define the effective focal length ( LFE).

few exceptions (very few) Point & Shoot cameras and so-called Bridge or Prosumer share a sensor size of 1/2.3 cryptically called ". The following is a list of common sensors used in these cameras (small sensors).

Some of the more common smaller sensors

sensors in blue are most common in small chambers,

all measurements are in millimeters .

an exercise of reasoning to understand how to distribute the photosites on the sensor, and how to calculate its size:

An example, my wife has a Panasonic Lumix FZ 100 , this is a good camera category or Prosumer Bridge is among the best (or best) of its level, many interesting features and other fantasy, a zoom ranging from 25 mm. to 600 mm. Effective Focal Length (a very good 24x zoom), has 14.1-megapixel (a good decision!), y. .. a 1/2.3 sensor! ??

If we see in the table above, we have that the sensor has a size of 6.16 mm . x 4.62 mm. , if we multiply both measures an area of \u200b\u200b28.46 mm. square, looking at the specifications of the camera have their resolution is distributed in 4.320 3.240 pixels and vertical pixels horixontales .

If we divide the number of horizontal pixels between the horizontal dimension of the sensor, we obtain as a result the number of pixels per sensor that captures miliímetro horizontally:

4.320 pix. / 6.16 mm. = 701.30 pixels x mm. (In the horizontal direction)

Now do the same thing in the vertical direction:

3.240 pix. / 4.62 mm. = 701.30 pixels x mm. (In the vertical direction)

From these calculations we can assume that the linear density (pixels x mm.) Is the same both horizontally and vertically, in each linear inch this sensor is 701.3 photosites (pixels .)

have to know how many photosites on a square inch, multiply 701.3 x 701.3, with which we get that this sensor has 491.821 photosites per square millimeter. This is almost half a million photosites in each millimeter square.

But, all this display of calculations ... it good for? ... serves to give us an idea of \u200b\u200bhow small are the photosites or components of a sensor like this is more so now let's see how each measures so we can compare them with other sensor photosites bigger.

If we divide an inch between the number of photosites, we obtain the linear measurement of each photosite expressed in thousandths of a millimeter or micron (micron), ie millionths of a meter. Thus:

1 / 701.3 = 1.43 microns. (Each photosite measures 1.43 microns in diameter.)

We assume that the photosites are round or square area (it's round), but we need to calculate the area of \u200b\u200beach photosite needed to do comparisons.

The important measure is the area!

Because most area captures more photons.

area of \u200b\u200bcircle = radius squared multiplied by pi. (Remember?)

==> A = 0715 ^ 2 x 3.1416 = 1.6 square microns

Thus, a circular photosite of 1.43 microns in diameter, have an area of 1.6 microns square.

If we compare the size of a photosite of a small sensor (camera point & shoot and bridge) with a DSLR (reflex), we realize the size difference.

I have an Olympus E 30 from 12.30 megapixel Four Thirds sensor of 17.30 mm. X 13 mm. If we make the same calculations, we see that the photosites of the sensor measured 4.30 microns linear, which is much larger, and if we do the calculations to find the area, we think this is 14.5 square microns.

Making the comparison (by dividing the latter area between the former), we have the photosites of my camera are more than 9 times bigger than the sensor of the Lumix FZ 100.

Now we see why the image quality of an SLR camera is far superior to that of a small camera (for those who do not have interchangeable lenses).

Following the same line, the Canon EOS cameras, model 7D - 60D-T3i, for example, have photosites of 4.31 microns in diameter, and therefore of 14.58 square microns area.

In comparison with my Olympus, we see that virtually the same size, but comparison FZ sensor 100, are still enormous.

I hope I explained and demonstrated that the issue IS NOT sensor size, ES the size of the photosites or elements of the sensor, referred to the area size.

Basically when you know about this issue talk about the size of the sensor, talk about the difference between DSLR cameras and which are not., As a Four Thirds sensor measuring 17.3 x 13 mm. and Canon's APS C measures 22.30 x 14.90 mm, it is true that the sensor is bigger, but what really matters is the size of the photosites, and these are practically the same ... let me understand?

And when those who do not speak or have not investigated the size of the sensor, ONLY talk about it, regardless of anything else.

worth mentioning that there are some cameras point & shoot taking high quality photos, good, better quality than the other P & S, but never of the quality of a DSLR. They do this by putting a little larger sensors, and lower the resolution ... this is, if not the right way to grow the photosites, more area and less number of photosites in the area ... I mean?

Well some of these cameras are the LX5 Lumix and Olympus XZ-1, its photosites are 50% larger than those of normal small cameras, but their prices are also larger. We also have the Canon Powershot G12 and Nikon P 7000 with its sensors 1/1.7 "and 10.1 megapixels. I do not know if there are others in this category, I will leave that to your research.

Then I pass a link to a Microsoft Excel table I made for you, in this table is a list of different brands and models of cameras, at least the most representative in terms of sensor size in This table is the sensor size and the number of megapixels that this is, then comes a red zone with sensor data, and their vertical and horizontal measures, the same bias and its area in square millimeters.

Then, in the blue area are data from photosites (pixels), the amount both horizontally and vertically, the number of photosites per millimeter in both directions, the density in pixels per square millimeter, the size (diameter) of micron photosite and finally the most important figure, the photosite area in square microns, this is the one used for comparison.

And to go to extremes I have a bridge camera, which has the sensor with photosites of a smaller area, and a digital back medium format Hasselblad 39 megapixel.

hope that with these two articles for the sensors, make it very clear that the cameras P & S, the bridge or prosumer, much less cell phones can compete with a DSLR (reflex).

Ah, it is remarkable the size of the photosites of the Nikon D700, a camera with better signal to noise ratio, so you can realizr shots with very high ISO values \u200b\u200bwith little loss of quality.

EYE, the fact that a camera comes with the possibility of raising the ISO to stratospheric figures does not necessarily mean that those values \u200b\u200bare used in practice.

Here comes the Excel link box: SENSORS

Other links:

Sensor Sizes in DPReview

Sensor Sizes in Cambridge in Colour

NOTE: The sensor size is determinate to find the multiplication factor, and / or the effective focal length (LFE) , which is directly connected to its diagonal, but we'll see later

I hope I have exhausted the subject (here come my knowledge).

See you at the next post!

Bridal Shower Card Sayings

Sensors Part I: The sensor size is very important? The subject of the resolution, sensor size and quality of a photo. Pressing the shutter

The technical quality of a photo depends first and foremost of the lens, without a doubt the most expensive element of the camera; second sensor, the electronic component that converts the image captured by the lens into digital information on light and color, third camera processor (each brand has its own), which manipulates the sensor data according programming each brand and model are the factory, and finally the resolution (megapixels) and dynamic range .

blog In this article, we discuss the sensor, so make yourself comfortable because there are a lot of bread by slicing.

SENSOR: a light-sensitive element, is in the place that was previously the film, ie in the focal plane. The sensor is responsible for capturing the scene projected by the lens and turn it into a series of digital signals (ones and zeros), which will be converted into a photographic image by the camera processor.

The sensor is composed of many sub elements (photosites), for simplicity we will call them pixels, as in a sensor usually be millions of these sub items, the unit used is the megapixel. Each pixel is arranged in a particular RGB color pattern, such as BAYER (the most known and used, but not only), and each pixel has color information and brightness at that point.

A CMOS sensor

There are two types of sensors, the CCD (Charge - Coupled Device) and CMOS (Complementary Metal-Oxide - Semiconductor) each has its advantages and disadvantages , but we will not discuss these issues in this post.

The megapixels are a unit of quantity, not quality, so a camera with a 14-megapixel sensor is not necessarily better quality than one with a 10-megapixel sensor, although those who are responsible for the marketing of the cameras we want convince you otherwise.

It is very common to listen to vendors and customers to discuss the issue of points megapixel camera sales, but is more common to see how they make buying decisions based solely on this parameter, is some people argue that their cell 5 or 8 megapixel camera takes pictures of equal quality to a camera with the same amount of megapixels. Indeed

is desirable to obtain good resolution for better detail in the photos, high resolution is important when printing in large sizes and when you want to cut some photos to enlarge the subject. Obviously the resolution (megapixels) is important, but not the only factor we must look

Others have heard or read that the sensor size is critical to the quality of the photos, and only make decisions based on this parameter, and if there is a camera with a sensor 20 x 20 cm. would rush to buy it.

But everything has a practical limit, both the number of megapixels as the size of the sensor.

The real secret is not the quality or the amount of megapixels or the size of the sensor, found on the size of the photosites, of these sub elements that capture the pixels one by one, they determine the quality of information for each individual pixel, and thus the overall quality, ie photo.

There is a factor that depends directly on the size of the light sensor element, and is The Signal to Noise Ratio (Signal to Noise Ratio):

Signal: is all relevant information about what you want capture, either a picture, sound or any other information.

Noise: is any unwanted information that inevitably captures along with the signal, reducing its capacity to interfere with it.

This signal and noise are also some relative, if you want to hear the conversation between two people and there music something back with the volume up, the conversation is the sign and the music is noise, but if I listen to music and two people speak very highly and / or very near, the music will be the talk signal and noise ... I mean? (The noise is interfering).

For example, if you're in town and want to listen to your radio, tune your favorite station and you're done. But the receiver also produces some unwanted noise, due to its electronics, noise that is totally inevitable and inherent to their status transistorized computer, with chips etc. But one does not hear the noise because the signal (music) is very strong and need not rise much the volume to hear properly, in other words the signal is so high that in comparison with it the noise is very low ... has a high signal to noise ratio .

Another time, if one is somewhere away from the city and want to tune your favorite station, but the signal is very weak because of the distance, then you have to turn the volume up and realizes that his music is inevitably accompanied by a nasty hiss (noise) that noise is always present, what is happening now is that the signal is lower than the rise volume (amplify), noise can match and even surpass, that is we now have more noise than signal making it difficult or impossible to hear the music, the radio now has a low signal to noise ratio.

If I failed to explain properly on the concept SIGNAL / NOISE, please write me to mail the blog and try to do better.

Just as in the example above, each sensor element produces its own noise, and the higher the signal to noise ratio, the more will the resulting image quality, the secret is to keep the noise as low possible to improve the relationship. The only way to do this is: using larger elements (sensor design itself), and maintaining the ISO VALUE as low as possible. Fortunately

self-noise level of an electronic element grows very little to increase its size, but not to increase their signal amplification, the ISO value in the case of the sensor.

To understand how it influences the size of the sensor elements in the image quality, let me illustrate the process with some examples:

If you put in the rain some deposits of different sizes, which one would receive or would capture a greater number of drops and thus a greater amount of water? (Assuming all time remain the same in the rain).

What deposit will receive more rain drops?

Obviously the larger container will collect more raindrops, the same way a larger photosite collect as much photons (light particles). Thus, the fact that a sensor is composed of larger items benefits the quality of a photo.

But that is not the merits, we saw the issue of signal to noise ratio, since each component of the sensor always produces a certain noise level, see what are the advantages of larger photosites:

Signal to Noise at ISO 100

As noted above, the size of a photosite affects little noise it produces (all electronic devices produce), but their size helps us to improve the signal- noise. In the small photosite photons have 9 and 5 units of noise, our signal to noise ratio will be 1.8; in the medium photosite have one more unit of noise, but we have more than twice as many photons as the previous, so our signal to noise ratio will be 3.67, as we see is higher than in the photosite small, since although noise is a little higher, the number of photons that can be captured is much higher, and now we see the larger photosite, which has a signal to noise ratio of 7, far higher than the other two.

Signal to Noise at ISO 800

In this graph we see what happens when you raise the ISO value, the units are automatically increased noise, now changing the signal to noise ratio in the three photosites, but with much greater IMPACT affecting the smallest element, whose ratio is now 0.56 and there is more noise than signal in the intermediate size we now have 1.8 of SNR, and is that the signal becomes twice the noise, yet is less affected than the smaller element, and finally the largest is now 4.1, SNR, showing his ability to work without a lot of high ISO values impact on the quality of your information.

could say then that the signal to noise ratio is the relationship between useful information and useless. Just as the "noise" appears on a radio with an annoying sound that interferes with the music, in a photo appears as a series of dots or small spots that interfere with the sharpness of the picture.

NOTE: The values \u200b\u200bused are only illustrative, plotted the principle of signal to noise ratio with different ISO settings, but they do represent reality.

Then some pictures taken with a pocket camera (point & shoot) with a small 14-megapixel sensor, with very good light and using ISO values \u200b\u200bof 80, 400 and 1,600, how we affect the ISO to the quality of a picture:

So, at first glance did not notice the noise (digital), high amplification product of signal with high ISO values, but look closer and you will realize, how as the ISO value increases, the signal to noise ratio gets worse, becoming louder the noise and reducing the sharpness and detail capacity the photo

Whereas a camera point & shoot, is a photo

with a level of detail acceptable.

By raising the ISO to 400 there is already a noticeable loss of detail.

By raising the ISO to 1,600 loss of detail in this photo

is unacceptable for anyone.

Click on each photo to enlarge

Well, now understood as sensors with larger photosites achieve better images?; Be seen how the larger photosites take more quality values High ISO?, Note that I said the larger sensors, but those with larger items, not necessarily the same thing ... see:

The following graph we have three sensors imaginary three different sizes, all three have the same resolution (192 pixels), but differ in size from the smaller sensor has an area that is the sixteenth part of the sensor and the fourth largest of the sensor medium.

If we keep constant the resolution, then the size of the photosites is proportional to the areas of sensors, so the smaller sensor will have some photosites that will be the fourth of the sensor photosites medium, and sixteen vece smaller than the larger sensor.

Click to enlarge

Which of these three sensors have the elements (photosites) bigger? ... obviously the 8 x 6 cm., then a resolution equal the larger sensor will have a better image quality, better performance at high ISO settings, better signal to noise ratio and better dynamic range.

In this case a larger sensor achieves better image quality (because the photosites are larger).

Now let's see what happens when you increase the resolution of the sensor 16 times larger, we now have much higher resolution (more megapixels in real life), this is what pushed us to buy in stores and in advertisements ... but I will have more quality with higher resolution?

Click to enlarge

By increasing the resolution without changing the area, we have no alternative but to use smaller elements, which puts the larger sensor in the same situation that the smaller sensor, both have the same size photosites ... realize? ... clear that there are additional considerations, usually the larger sensors found in cameras reflex (DSLR), and these are best small camera lens fixed lens, whereupon the better part of a sensor basic point & Cameras shoot and / or bridge (prosumer) DSLR cameras additionally have more powerful processors, and better resources for digital filters and stuff, that's why we have achieved in a similar situation to get more out of its sensors, even when they do not have huge photosites.

Cameras Types

I hope I have clarified some doubts about the size of the sensors, the resolution (the famous megapixels), its impact on picture quality and ISO.

In the next post we will pursue the subject of the resolution and some real life figures obtained from the data of some camera manufacturers.

Until the next post!

UPDATE !!... Sensors Part II is released!