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Number of pixels

This Topic will focus on digital sensors, which are at the heart of modern cameras, by following the path of image formation. It will show the benefits and limitations of digital photography technology and help decipher the true meaning of the announcements made by manufacturers about the performance of their devices.

The number of pixels will have a direct impact on the definition of the image, that is to say on the finest details observable, thus on the maximum size of the enlargements that will be possible to make.

The minimum density of the printed dots to obtain a very good close-up image is 300 dpi (dots per inch, i.e. “dots per inch”) assuming that a printed dot is equal to one pixel.

Is the number of pixels important ?

Here is the approximate result for some classic formats:

10×15 cm = 2.10 million pixels;
13×18 cm = 3.264 million pixels;
18×24 cm = 6 million pixels;
20×30 cm = 9.5 million pixels.
For comparison, a 23′ (51×29 cm) wide LCD display uses only 2 million pixels.

Number of pixels and magnifications

This gives a good idea of the maximum size of magnifications that can be obtained depending on the definition of the sensor. However, this criterion of 300 pixels per inch must be nuanced, because for large-format enlargements intended to be seen at a certain distance, a smaller definition is generally acceptable.

It is therefore obvious that the number of pixels of modern sensors far exceeds the real needs of the majority of users, but we must not forget that there is a large category of amateurs who are passionate about quality photography and who produce images that many of them have nothing to envy to those signed by renowned artists or professionals. It is for these, mostly reflex users, that this parameter acquires real importance.

So the real limiting factor no longer resides in the sensor but in the quality of the lenses. However, quality lenses cost as much or much more than a case, which explains the advice often given: it is better to buy a case that is less expensive than the one that makes you want, but to offer a very good lens.

It is also important to know that there are for professionals digital backs with large size sensors adaptable on medium formats (genre Hasselblad or Mamiya), or even on photographic chambers of studio, but these accessories cost a real fortune, are complex to use and many can only be connected to a computer. That’s not going to happen here.

In reality, we will discover that this number of pixels is a fictitious value, which relativizes a little the previous calculations.

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