In combination with the Live View function camera displays allow compositing, capturing and filming a scene. Also a later assessment of the image and related adjustments are possible. The monitors vary in size, resolution and functionality, depending on manufacturer and model.
The stated size of a display normally refers to the diagonal of the screen and is given in inches. For converting the size into cm, just keep in mind that one inch equals 2.54 cm. Generally, the monitor diagonal of a camera display is 3" (inch). But also cameras exist, whose monitor is with 2.7" respectively 3.2", below or above that. While the one or another compact model represents the subject on a smaller screen, the display of some pricier system cameras sometimes turn out larger.
The resolution varies as the dimensions. Thus, on the monitor area there can be between 230.000 and 2.359.000 dots. But be careful, the indication “dot” is not “pixel”, but rather so-called subpixels. Thereby, three dots (RGB) usually build one pixel (see en.wikipedia.org/wiki/Pixel_geometry). In the following illustration, one pixel contains the three subpixels RGB
As example, a camera monitor with 921.000 dots, contains 307.000 pixels.
The more pixels the higher the display resolution, so far so good. But a high amount of pixels alone is not decisive for how detailed we perceive a display image. Additionally, the monitor size and viewing distance have influence on it.
For viewing an image that is well resolved and without pixel structure, the individual pixels should be appropriately small. Otherwise, these would be visible for the eyes. The size of a pixel results due to the screen size and the pixel count. For better understanding, we look at three equally large surfaces with different resolutions.
Thus, a higher pixel count seems better than a lower for viewing. Basically right, as long as the display size remains the same. If it varies, it also influences the size of the pixel. For this reason, smaller monitors get along well with a slightly smaller resolution.
Pixel density – ppi
However, the pixel amount itself is not decisive. The resolution is rather to set in relation to the monitor size. This is possible with the pixel density (ppi – pixel per inch) that indicates how many pixels are present on one inch.
Theoretically monitors can be well compared by the pixel density. But how high should it be so that we can benefit from a good preview? It is difficult to point out a precise value. As a benchmark, it is often referred to the resolution of the human eye. With this it can be described up to which grade the eye can differentiate fine details, thus two points can be perceived separately.
Resolution of the human eye
For the resolution of the human eye a value of one arc minute is given pretty often. This means that the eye can detect two points separately if the angle distance between those two points is at least on arc minute or if the two points have a certain distance to each other. Thereby the stated value of one arc minute refers to a normal sighted viewer (see en.wikipedia.org/wiki/Visual_acuity#.22Normal.22_visual_acuity).
Unfortunately, this specified minimum visual angle does not directly indicate if the pixel density of a monitor meets the requirements of our sight. For this reason, some mathematical calculations are necessary:
To find out, how many pixels our bare eyes can perceive on one inch, we can calculate the distance (a, b, c) that two points at least need to have to each other. However, this point distance depends on the viewing distance (A, B, C). The lower it is, the closer the points can be. In other words: with a shorter viewing distance the eye can resolve finer details.
By calculating the distance of the two points for a certain viewing distance, it can be determined how many pixels can be placed on one inch. For a better relation to the digital display, the indication points / dots per inch might be a bit misleading. A point correlates to a pixel and not to a dot / subpixel. Because of this, we replace the term “dots” per inch by “pixel” that is subsequently used.
Low pixel density
The above calculated values are based on normal visual acuity, where a visual angle of 1 arc minute is assumed. But the visual acuity of people may vary and also coincides with increasing age (see cms.augeninfo.de/uploads/media/PM_Mehr_als_100_Prozent_sind_moeglich.pdf). Therefore, the stated visual angle of 1 arc minute should be taken as reference.
For clarification: With a weaker eye resolution of an observer, the requirements to the monitors reduces. This is due to the corresponding minimum visual angle that enlarges with lower visual acuity. For example, if a lower visual acuity exists that is not corrected by glasses, a monitor with a lower pixel density also can give a good preview. But when monitor offer much less and bigger pixels, the eye will recognize them and the quality of the preview impression will be reduced.
High pixel density
So it seems convenient to prefer displays with high pixel densities. But here also the human eye and the viewing distance set natural limits. A high ppi value is not necessary beneficial, but can be. For clarification, we take the following scenario:
Looking from a distance of 11.8 inches (300mm) at one monitor with 300 ppi and another with 400 ppi, both would not differ for a normal sighted observer. The reason is that in this case the eye itself can only resolve up to 282 pixels per inch. Even if a display offers a higher pixel density, thus more fine details, the eye could not see respectively resolve them.
Now if observers have a better visual acuity, it is possible that they can see the individual pixels on both monitors. Here, a higher pixel density is definitely advantageous.
On the other hand the pixels could also be seen by a normal sighted person if the viewing distance is reduced. As already mentioned, the eye can perceive finer details with decreasing distance. If you would shrink the distance between eye and monitor, for example to 7.9 inches (200 mm), a normal sighted observer could resolve up to 437 pixels per inch at a reduced viewing distance of 7.9 inches. Thus, single pixel would be visible at both of our example displays.
Normally the camera display is not used at such short distances, even if it is possible due to a sufficient high pixel density.
The monitor of many compact and system cameras is movable. That means that it can be tilted, folded or rotated. There exist camera models, whose display can be folded out and tilted up to 180 degrees up- or downwards, for example. Instead other camera monitors can be flipped out and be rotated. Thus, due to a rotation of up to 270 degrees diverse shooting perspectives are possible. Additionally a display that can be rotated / tilted to the camera body, offers additional protection against damages.
What is the advantage of movability?
There are many advantages, depending on how flexible a monitor is. One concerns the handling while shooting from different angles. Take, for example, a cat that you would like to capture at eye level. With a rigid built-in display you have to knee or lie down, to bring the monitor parallel to the motive. Is the display agile and can be rotated / tilted 90 degree upwards, you only have to lower the camera position. The tilted / rotated monitor allows now viewing the monitor from above and an uncomfortable shooting position therefore is unnecessary. The same applies for huge or high subjects. A display that can be tilted / rotated to the bottom ease our shooting position, when we cannot move to a higher area. Some monitors are such flexible that even self-portraits can be recorded. However, the larger the device, the awkward a Selfie may be.
Another little advantage using a flexible display shows when the sun shines. Since reflections can disturb the display view, the incident light can be regulated a bit due to small changes of the tilt or rotation angle. However, in extreme sunlight often only the viewfinder allows a good representation.