Motion pictures or movies started with capturing images on film, which used to be a 35mm film. This is the film that we see as negative, which is used to develop photographs. The 35mm film is actually a 36mm X 24mm film and this is known as full frame. Then technology advanced and sensors came into being. But the new and advanced digital cameras were not initially capable of accommodating the full frame size into the sensor, so this led to the development of crop sensors. The crop sensors were smaller in size and format than the full frame sensor. These are also known as APS – C sensors. These sensors are also based on a film format, known Advanced Photo System – Classic or APS – C. The size of these sensors is around 24mm X 15mm. It is thus, approximately 1.5 times smaller than the full frame sensor. Point and shoot sensors are even smaller and bigger sensors than full frame sensors are also available. These bigger frames are known as medium format sensors. Brands like PhaseOne, Hasselblad, Fujifilm etc. make such sensors.
How does the size of the sensor affect our photographs? For this, we need to understand what is image circle. We ought to be familiar with this fact that photographs are formed when light passes through the camera lens and falls on the camera sensor. The projection of the image created on the sensor is known as the image circle. As the sensor size changes, what changes is the focal length of the camera lens used in a camera. So, the full frame camera picture quality won’t be affected but when we consider crop sensors, then they’ll only be able to capture the central part of the image circle. This gives the illusion that we have zoomed in on the image. This is because the focal length of the lens has changed in case of the crop sensor. As we now know that crop sensors are 1.5 times smaller than the full frame sensors, this implies that the focal length for crop sensors is going to be 1.5 times larger than that for the full frame sensor. So, a 50mm lens would give out the illusion of a 75mm field of view, which is 1.5 times of 50mm.
Crop sensors are comparatively cheaper than full frame sensors, hence this cost reflects in the cost of cameras. However, this does not convey that crop sensors are inferior to full frame sensors. Each has its own strengths. Crops sensors are really advantageous for wildlife photographers as a 300mm lens for them will give out the illusion of a 450mm field of view. This allows them to capture really detailed photographs of the animals in their natural habitat, without disturbing them at all.
Keep in mind that sensors are not everything that determines the quality of a camera. The processor and colour science is also very important to determine the final output, i.e. the photograph.
It is known that more megapixels mean great picture quality, as in more details in the picture, but the more megapixels a sensor has, the chances of noise increase, especially at high ISO. Smaller sensors are prone to having more noise than bigger sensors. This is the reason why Nikon D5, the most expensive camera by Nikon, has only 20.8MP and Sony A7SII, one of the best low light cameras, has only 12.2MP.
Depth of field is also linked with sensor size along with the aperture. For instance, if we use a 50mm lens on a micro four thirds sensor, which is almost half of the full frame sensor size, then its focal length will be around 100mm. But if the aperture of 50mm is 1.4, then its depth of field will act similar to that of a 100mm/2.8 lens. Hence, the smaller your sensor gets, achieving shallow depth of field gets more difficult. Shallow depth of field would mean that the focus lies mainly on your subject, the background gets a bit blurred out. It might be advantageous in many situations like some portraits or in cinema, but for news coverage this is not at all significant. Small sensors can help achieve deep depth of field which can be an advantage for certain applications or scenarios.
Going into technical specifications, teaches us one thing that we need to experience it ourselves. There is no best or worst in such cases. You need to understand the situation and your requirements and choose accordingly. There are no rules when it comes to projecting your creativity. What goes best with what is up to you. As you get out there and shoot more and more pictures, use varied cameras, different lenses, you’ll eventually learn a lot about their pros and cons.