SLR cameras show the image that will actually flow to the sensor in the viewfinder. They do this by using a mirror in front of the sensor and reflecting it in the viewfinder. The problem arises in the second reflection: we need to get a 90-degree rotation to get the image on the viewfinder, here comes pentaprism or pentamimar
Let's look at the principle behind this first, it will be easier to explain this with pentaprism, so we’ll talk in terms of pentaprism, and then explain the difference with that with regards to pentamiror.
Since this image shows that pentaprism does the work of turning the light 90 degrees. The internal reflection inside the prism turns the light into 90 degrees. The image from the lens is reflected by a mirror, which then falls on a prism that rotates it 90 degrees and sends it to the viewfinder. The work of the prism is as simple as it is explained. Remember that our interest is to find out how different pentamorrholes and pentaprisms are different and why these two exist and which ones to choose.
Now, depending on the form factor of the sensor, the amount of light that is reflected in the viewfinder changes as smaller form factors require less surface area and, therefore, less full light to reflect. In simple words, the reflecting mirror will be smaller, the amount of light is directly proportional. Thus, when using a smaller sensor, the light that we have to deal with is, first of all, smaller. Secondly, we must understand that the reflection of mirrors reflecting the reflection of air has a greater loss of light than the internal reflection in a good quality material.
In the system of mirror reflection, the arrangement of the mirrors does the work that the prism does, because here the reflection on the mirror with air as medium, the loss of light is greater. It is here that pentaprism is emulated by a series of correctly positioned mirrors. These mirrors, however, have air as the medium between this reflective design, but this results in a good amount of light.
Now why does the light lose such a problem? When we view the viewfinder, especially in low light conditions, if the image is not bright, it will be difficult for us to determine the focus correctly and other similar details. In addition, when using a smaller form factor sensor, the amount of light is inherently low, so there is an additional decrease in brightness. Another problem would be the difficulty in correctly defining contrasts.
If brightness is so important, why do we have pentamiror systems? This can be explained only by one word “cost”. Mirror-based design is much cheaper than a prism-based design, because prisms are expensive. Manufacturers are always trying to reduce costs to make their products more popular. They compromise quality to do it. An interesting fact is that, although there may be a brightness loss of 10–20%, the design of the pentamorrhoa has many important advantages over the design of the pentaprism.
The main advantage is that it is cheaper. Another advantage is that the design of the pentamiror is lighter, the reflex camera is a heavy piece of equipment that adds part of the lens to it, and everyone makes it quiet, so reducing weight is a good advantage.
Currently, pentaprism projects typically have a good viewing area of 95% or more, the viewing area is the percentage of the image area that falls on the screen, which can be seen through the viewfinder. This is important because when the percentage is lower, we do not see the edges of the image through the viewfinder.
Most of today's budget DSLR and downstream DSLR proximers use pentamirror to offer better prices and lighter bodies. If you are in low-light photos or need a bright viewfinder, you should look at the pentaprism model. In general, pentaprism is a sacrifice that you can make without much frustration regarding the price advantage.
