Lens Focal Length:
Understanding Lens Focal Length And Crop Factor – Focal length is the distance found between the center of the lens and the focal plane (camera sensor). DSLR camera focal lengths are usually specified in millimeters and are given the symbol f, for example 18-55mm for kit lenses, 10-16mm for wide angle lenses, and 55-300mm for telephoto lenses.
The camera’s focal length functions to determine how wide the total area is on an object that we can shoot. In addition, the focal length on the camera also determines how wide and narrow the focus area (read about the depth of field) of the main object being photographed, in other words that the camera’s focal length affects the perspective of object magnification.
A camera that has a short focal length will provide a wide perspective (wide photo area) (wide lens). Then the focal length of the camera which has a medium focal length of the lens, will provide an object magnification perspective with a normal view (kit lens and fix / prime). As for the focal length of a camera with a large lens focal length it will provide a perspective of magnification of narrow objects (telephoto lenses).
So do not be surprised when looking at photos that show a certain perspective, because usually photographers have different types of lenses with different focal length lenses, this adjusts to the needs and tastes of the photographer himself.
Types of Lens Focal Length Based on the Perspective :
1. Ultra Wide Angle Lens (10-16mm). Produces a wider view of the scene than a standard lens, making objects appear smaller than normal lenses. It has an extraordinary DoF (Depth of Field), so that its short focal length allows a photographer to take photos with the same focus from the foreground to the background. Used for photographing natural landscapes (landscape).
2. Wide Angle Lens (16-28mm). Often used to photograph landscapes, architecture and interior photography. Lens that has a focal length of 16-28mm is useful for photographing objects in locations where it is not possible to move backward to load the entire view of the desired object.
3. Normal lens (28-40mm). Used for shooting 3/4 body model photos and full body models photos, or for group shots with a small number of people.
4. Short Telephoto Lens (40-60mm). Also known as a portrait lens. Lenses that have a focal length of 40-60mm provide a perspective or view of the head and shoulders from the photo model.
5. Medium telephoto lens (60-135mm). Lens with a focal length of 60-135mm is very popular for close-up photos and macro photography because it can be used at close distances between objects and cameras.
6. Long telephoto lens (135-300mm). Useful for enlarging photo objects that are too far from the camera. The lens with a 135-300mm focal length is very helpful in shooting an art concert on stage, sporting events and candid photos. Certain techniques are needed to minimize the effects of shaking which can impact on the reduced sharpness of the images (read about shutter speed).
7. Super telephoto lens (300mm and above). Lens with a focal length of more than 300mm is very useful for photographers who shoot hundreds of meters or small objects with a distance of tens of meters. This lens is often used for photographing sports activities, which makes it impossible to take photos from close range (try to pay attention to photographers at football matches that are broadcast on television).
But despite all that, the size of the camera’s focal length is not the same as the physical size of the visible lens. If there is a focal length camera that uses a lens (with a focal length) of 300mm, it does not mean that the physical length is also 300mm (30cm).
Lenses available for DSLR cameras are now sophisticated due to technological advancements, because they use many optical elements in them that synergize into a combination. So that the physical length of the lens can be shorter (easier to carry by hand).
Crop Factor :
If you often read the specifications of a DSLR lens or camera and or you like reading articles and photography forums, one of the terms that often arises and makes us wonder is this: Crop-Factor, Crop Camera, APSC, Focal Length Multiplier and 35mm equivalent. All of these terms refer to Crop-Factor. This article will try to explain the understanding of crop factors in a short and easy way.
The photography industry has been referring to 35mm film for decades, now when digital cameras have sprung up with a variety of sensor sizes smaller than film size, so to avoid confusion, the sensor size is compared to film size. Digital SLR cameras that have sensors the same size as the size of a film are called full frame DSLR cameras, for example: Nikon D4, Nikon D800, Canon 5D, Canon 1Dx.
Crop cameras are cameras that have a smaller sensor size than film size. It is called a crop camera because when a lens is mounted on a full frame camera shows a photo area that includes (for example only) the mountain and its fields, then when the same lens you attach to this crop camera the photo area will be cut off (crop) so that it only covers only the mountain only, so the photo area narrows. The smaller sensor size cuts the full view produced by the lens.
Now crop factor is a count of how the cutting factor occurs. As an illustration, see how a smaller sensor cuts a photo object when compared to a full frame camera (35mm film):
Read to Lens Auto Focus Tuning
While the other line is the crop factor of some compact cameras whose sensor size is much smaller.
Crop factor influences the equivalent focal length of a lens (read about focal length here). A lens with a focal length of 18mm when mounted on a Nikon APSC camera that has a crop factor of 1.5 then the equivalent focal length (in the standard 35mm) is (18 times 1.5) equal to 27mm. While a 12mm lens when mounted on an Olympus OM-D camera has a 2x crop factor, the equivalent focal length of 35mm is 24mm.