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The Canon EF-S 17–85mm f / 4–5.6 IS USM is a standard zoom lens for Canon digital single-lens reflex cameras with an EF-S lens mount and image stabilization. [1] [2] [3] The EF-S designation means it can only be used on EOS cameras with an APS-C sensor released after 2003.
Canon now sells an image-stabilized 16–35mm f / 4 lens for about $300 more than the 17–40. This lens is also a popular step up from the stock kit lens on many of Canon's EOS Digital family of cameras, the EF-S 18–55mm f / 3.5–5.6 , for those still wanting a wide angle lens.
f / 1.2L USM f / 1.2L II USM f / 1.8 USM f/1.4L IS USM Image Key features Full-frame compatible Yes Image stabilizer No Yes Ultrasonic Motor Yes L-series Yes No Yes Diffractive Optics No Macro No Technical data Aperture (max-min) f / 1.2 – f / 16 f / 1.8 – f / 22 f / 1.4 – f / 22 Construction 7 groups / 8 elements 7 groups / 9 elements
It is praised as "one of the best general/multi-purpose lenses available", [1] [2] and ideal for available light photography on a Canon APS-C camera. [3]The fast f / 2.8 aperture, combined with 3-stop image stabilization, makes the 17–55 very useful in low light compared to an unstabilized f / 3.5–5.6 Canon EF-S 18–55mm lens, which is a frequent kit lens, and thus the 17–55 is much ...
Notation for the (principal) square root of x. For example, √ 25 = 5, since 25 = 5 ⋅ 5, or 5 2 (5 squared). In mathematics, a square root of a number x is a number y such that =; in other words, a number y whose square (the result of multiplying the number by itself, or ) is x. [1]
A root of degree 2 is called a square root and a root of degree 3, a cube root. Roots of higher degree are referred by using ordinal numbers, as in fourth root, twentieth root, etc. The computation of an n th root is a root extraction. For example, 3 is a square root of 9, since 3 2 = 9, and −3 is also a square root of 9, since (−3) 2 = 9.
A method analogous to piece-wise linear approximation but using only arithmetic instead of algebraic equations, uses the multiplication tables in reverse: the square root of a number between 1 and 100 is between 1 and 10, so if we know 25 is a perfect square (5 × 5), and 36 is a perfect square (6 × 6), then the square root of a number greater than or equal to 25 but less than 36, begins with ...
When a Canon Extender EF is attached, the usual f-number compensation is applied (in the previous example of f/5.6 at 5× magnification, the effective f-number would be f/180 if the Canon Extender 2× was attached to the lens.) Magnification is continuous, not discrete, so fractional magnification values (for example, 2.3×) are possible.