How to Test Lens
A lens is the most important part of a camera. Here are some tips on how to test lens while purchasing.
Lens is an engineering marvel, which is developed with advance optical design, mechanical movements, electrical and electronic components. This technology is further assist by refined chemistry, materialization and craftsmanship. However, it is a product for commercial sale. So it has to be manufactured in commercially viable manner, and that is where we find so many makes of lenses, which has same type of design and feature, but at different price.
For SLR and DSLR cameras, apart from original camera manufacturer, there are other lens manufacturing companies, which make lenses, which are compatible with the camera body. So whenever we are purchasing a new (or a used) lens, we must consider following parts for its quality and performance.
By testing and understanding the lens and its limitations, we can take best out of it. All good lenses are made to perform best at all aperture settings, all focusing distance and if it is a zoom lens, then for all focal lengths. However, because of the limitations of physics and optical science, lens are bound to shift from optimum performance towards its average performance.
So how to test a lens? Basically, there are two different considerations in a lens test. One is mechanical and electrical parts, and other is its optical. Though the quality of an image depends on optical components, mechanical parts must support the optical part to perform and at the same time, they should give a user friendly and durable construction, which is easy to use and long lasting.
Lens testing is an experiment, which gives us experience and confidence on how to use a lens in most effective manner.
Overall points, we must check, are:
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
Other information on the lens: Indication and information given on a lens barrel
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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