Important pictures? Not with a smartphone!

Important pictures? Not with a smartphone!

25 March 2022 0 By Oscar Giacomin

When advising clients about communication we often debate about the quality of pictures taken with smartphones, as I don’t think they are ideal for use in flyers or other printed media.

Photography is the handwriting of light and if the sensor is tiny, the working light too is limited. 

I am not among those who criticize a priori the cameras of the smartphone. I am aware that they do miracles, but at the same time I believe that smartphones were not conceived to take still life pictures intended for billboards or magazines, but rather they are ideal to take great photos to publish online or to print in small formats.

From this point of view, resolution may be the least important attribute, more relevant is to evaluate exposure, noise reduction and color rendering. There is still a lot of work to be done in this domain, although it in terms of the simple piece of aluminum, glass and silicon (in other words the phone and its components), we have reached the end of the line. Today, and not due to the absence of technological progress, the camera components inside smartphones have reached a point where it is difficult (if not impossible) to go even further, even for cost reasons. Mathematics says it, spaces say it.

When a manufacturer highlights the quality of the camera in a smartphone, it often refers to a larger sensor and the larger pixels capable of capturing more light and brighter lenses. But smartphones have a mandatory constraint, and we must start from this constraint to understand the choices that were made and all other numbers: the constraint is thickness. A smartphone today is about 7mm thick: the camera module, which includes sensor, lens and stabilizer, must fit in these 7mm.

In photography there is a number that acts as a reference for everything, and this number is the distance, or focal length: the focal length indicates the distance between the optical center of the lens and the sensor plane focusing on the image. When combined with a sensor of a certain size, the focal distance determines the field view’s angle, that is, the area that is framed. For this reason, it was decided to use a reference sensor, and the choice was a 35mm (24mm x 36mm) unit. This has the dimensions of the frames of the old film used in full frame cameras. If you mounts a 200mm lens on a full frame sensor, the distance between the sensor plane and the center of the lens is really 200mm, as 50mm is the distance from the sensor to the center of the typical lens for portraits.

Once the angle of view is fixed, if the size of the sensor is reduced, the focal distance is reduced too. In talking about smartphones, the focal distance is a sort of structural constraint: if the smartphone is 7mm thick, removing a millimeter for the screen and 1mm for the body will leave 5mm. Considering that the sensor has its own thickness and that there are the electronics in the middle and that the lens is not flat, the end result is even lower. The focal distance of an iPhone 8 Plus, for example, is 3.99mm: between the sensor and the center of the lens there are practically 4mm. They could have been 3mm, but this action would have made it necessary to use an even smaller sensor: this explains the lump on the back of smartphones, it might not be aesthetically pleasing, but it does provide the manufacturer with the 1mm extra that is needed. 

The game is simple: given the same angle of view, a larger sensor requires a longer focal length (and it would not fit in the body of the smartphone). On the other hand, a shorter focal distance would require a smaller sensor. 

The focal distance is obtained by analyzing the Exif data. These are metadata of the jpeg file that store shooting parameters and lens data. If we used any application to open a picture taken with an iPhone, we get a message “focal distance 4mm equivalent to 28mm.” The distance between sensor and lens would be 28mm if the sensor was a full frame, but since the sensor is much smaller, it is only 4mm. Same “shooting” angle, same captured portion of the scene but the numbers at play is much smaller.

Two other factors now come into play: resolution and lens. As far as resolution is concerned, it is easy to understand that if the sensor has a given size dictated by the calculation made before, the more megapixel we use the smaller these pixels have to be. Twelve megapixels is the resolution that today allows larger pixels, capable of collecting more light, and offering a perfect resolution even on 4K TVs. A 20 megapixels’ sensor with large pixels is larger and would require a bigger focal distance length. The Lumia 1020, with its 41-megapixel sensor, had a focal distance length of 6.6mm. As a result, the smartphone had a thicker body and camera lock protruding visibly.

It is therefore useless to keep on analyzing the shots at 100%: from this point of view, it is really difficult to improve, and with the sensor of a smartphone you can never get the cleanliness

and the sharpness of an SLR or an APS-C camera. In evaluating a picture taken with a smartphone, therefore, different parameters should be considered, such as dynamics, color rendering, management, exposure, and flash. These parameters would truly tell who has invested to improve the camera, versus those that simply focused on developing a good photo module.

 

Oscar Giacomin  / General Manager, Facto Edizioni

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