Indications and Information on Lens
Engraved information on lens barrel gives us more indications of lens design, its range and quality. We must check each term, written on the lens by referring the instruction manual of the lens.
A good lens should have a distance indication scale, which shows how far the focused object is, from the camera. When we are using a manual flash light for shooting, we have to know the distance between the camera and the object, for setting the shooting aperture. In rare case, when we cannot view the frame, we can simply measure the distance and pre-focus the lens for focusing and take a picture without looking in the view finder.
Depth of field scale is another useful information, a lens should display. This scale gives us indication of how much we are getting as a depth of field. It is also very useful when we have to set the focusing for hyper focal focusing distance.
If you are interested in infra-red photography, then look for the red dot on the focusing ring. This dot is for infra-red photography focusing, and after manually focusing the object , we have to refocus the lens by shifting it to the red dot marking.
Lens barrel may have some numbers like 1:1.8, 1:2.0 etc. These numbers indicate the maximum aperture opening, on which the lens can be set. So in this first case, the lens has maximum aperture of f 1.8 and in second case, it is f 2.0. Lower the number, more is the diameter of aperture opening and costlier is the lens.
Zoom lens generally shows two aperture value for its maximum aperture setting. The marking may read something like 1: 2.8 : 4 - or it can be 1: 4 : 5.6
These types of value, given on the lens (of aperture) is for minimum and maximum focal length. This means that if the range of a zoom lens is say 18 mm to 55 mm, then at 18 mm, the lens can have widest opening of f 2.8 and when you zoom in at 55 mm focal length, then the lens will become slower and the same maximum lens opening will be as effective as f 4.
Some other information on lens like "Asymetrical" and "Multi-coated" indicates the design feature, and how far a lens is corrected for spherical aberration and flare. All these information can give us fair idea of the quality of a lens.
Apart from these general information on lens, some brand shows lens series, which indicates the quality of lens.
Read about this:
Aperture of lens: What we should check in aperture setting of a camera lens
Built, finish and weight of a lens: Why finishing and weight of a lens is important
Focusing mechanism of a lens: Different type of focusing mechanism of a camera lens
Lens faults: Various types of faults a lens can have, and how to check it
Range of focal length: Range of zoom lens in terms of focal length
Sharpness of lens: Resolution and lens contrast - how to test it
Zoom ring: Ring on a lens barrel for zoom and focusing
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