EF17-40mm f/4L USM

EF17-40mm f/4L USM

During interior photo sessions, it is often impossible to move far enough away from the subject. Such situations call for a high-performance zoom lens covering the range from ultra wide-angle 17mm to a standard 40mm angle of view. This configuration also makes it possible to vary the perspective to create unique photos of landscapes and other scenes. Aspherical lens elements of two types – one GMo element and two replica elements – combine with one Super UD lens element to effectively prevent aberrations, ensuring the sharp imaging performance that characterizes L-series lenses. Highly resistant to both dust and moisture, this lens also features a circular aperture for pleasing background blur effects.


  • EF17-40mm f/4L USM, 1/500sec., f/11
  • EF17-40mm f/4L USM
  • EF17-40mm f/4L USM
  • EF17-40mm f/4L USM


Angle of View
(horizontal, vertical, diagonal)
93°−49°20’/ 70°30’−34°/ 104°−57°30’
No. of Diaphragm Blades 7
Closest Focusing Distance 0.28m
Maximum Magnification 0.24x (at 40mm)
Water/dust Resistance Yes
Filter Size 77mm
Max. Diameter x Length Ø83.5 × 96.8mm
Weight Approx. 475g
Extension Tube EF12 II 0.83−0.32x
Extension Tube EF25 II 1.02−0.70x
Lens Cap E-77U / E-77 II
Lens Hood EW-83E
Lens Pouch/Case LP1319

  • Super UD element
  • GMo aspherical lens
  • Replica aspherical lens

MTF Characteristics

Spatial frequency Maximum aperture
10 lines/mm
30 lines/mm
How to read
MTF characteristics

Spatial frequency Maximum aperture
10 lines/mm
30 lines/mm

The more the S and M curves are in line, the more natural the blurred image becomes.

Modulation Transfer Function, or MTF, is a method of evaluating lens performance using contrast reproduction ratio. When evaluating the electrical characteristics of audio equipment, one important measure of performance is frequency response. This indicates the fidelity of the reproduced sound with respect to the source sound as it passes through the microphone, recording and playback circuits, and finally the speakers. When the reproduction is accurate, the equipment is classified as “hi-fi,” or “high fidelity.”
In the same way, when a lens is viewed as a transmission system for optical signals, measuring the frequency response of the optical system reveals whether the optical signal is transmitted faithfully. For a lens, the equivalent of frequency is “spatial frequency,” which indicates how many patterns, or cycles, of changes in sinusoidal density are present in a 1 mm width. Accordingly, the unit of spatial frequency is lines per mm, as opposed to Hz in electrical systems.

The MTF characteristics shown on this website are 10 lines/mm and 30 lines/mm, where the horizontal axis indicates image height (the distance on a diagonal line from the center of the image, in mm) with the image center set to 0, and the vertical axis indicates contrast. The closer the 10-line/mm curve is to 1, the better the contrast and clarity of the lens; the closer the 30-line/mm curve is to 1, the better the resolving power and sharpness of the lens. Although a good balance between both of these is important for a lens to be sharp and clear, a lens is generally said to offer excellent image quality if the 10-line/mm curve is greater than 0.8, or satisfactory image quality if greater than 0.6.

Resolving power and contrast are both good

Contrast is good; resolving power is poor

Resolving power is good; contrast is poor