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Digital Reflex and Crop Factor

Depending on the reflex model used, the field angle may vary depending on the sensor model that our reflex mounts. The smaller our sensor, the smaller the field angle, with the same focus, it will be small. As mentioned above, focal measurements refer to film or a 35mm (full frame) sensor. Many reflex models use sensors smaller than the full frame, the most common and amateur-level use the APS-C model which has a multiplication ratio of 1.6x compared to 35mm. A sensor covers a closer view than the one captured by the lens, as shown in the figure, but the lenses are designed to make the most of a full frame sensor. Using an APS-C sensor we will cover a smaller surface area and proportionally reduce the field angle equal to the multiplication or crop ratio. This means that we need to recalculate the focal effect according to the crop factor of the sensor that mounts our reflex. In the case of APS-C sensors, a 50mm lens will be equivalent to an 80mm (50mm x 1.6) lens. The advantage of the crop factor of the APS-C sensors is definitely to decrease the field angle to the same goal on FF with the same effective Focal length (LFE). This can be an advantage in sports and naturalist photography in view of the fact that decreasing the angle of the field we have a magnifiing effect of the image. On the contrary, it is negative in photographs where you need to use the big angle. This inconvenience led to the construction of specific large-agonal optics for APS-C sensors with a focus equal to 10mm

How to choose the focal length to use.

There is no rule to say what is the right goal to be mounted to take a photograph, but we can give some important indications to make the correct choice for the shot of the photograph that we have in mind. By summarizing what has been said so far, we can see what are the main characteristics of the three macro categories of the focal.

  • GRANDAGOLI Wide Field Angle allows you to store a large amount of elements in the frame and has a wide depth of field.
  • NORMAL or STANDARD function. They provide a field angle similar to that of the human eye
  • THE TELESORS. Narrow field angle, reduced field profodity. In addition, the telephoto lenses crush the image by reducing the distances between the various planes of the photograph.
Knowing the unique characteristics of the various types of lenses helps in deciding which one to use to make our shots.
In this paragraph we mentioned the depth of field that we will see specifically in the dedicated chapter.

Two exercises to see in the field the differences that you have using different focal points on the same subject:

1. Shoot a subject from the same distance using a wide-angle, standard focal, and a lens.

2. Fill the frame with the same subject as you approach or move away from the subject and using a grand-agolare, standard and telephoto lens optics.

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