17-40 f4L

What is the Canon “L” Lens Series?

Good question – and many answers exist, but it is Canon’s professional line (though used extensively by non-professionals) of EOS EF autofocus 35mm SLR and DSLR still camera lenses. Some say L stands for “Low Dispersion” – achieved by the UD lens elements found in these lenses. But, the true answer is probably the one in Canon’s Lens Work III Book – “L” is for “Luxury”.

Watch the sidelines at the next professional sporting event you attend or watch on TV. Look for the identifying L-lens red stripe around the end of the photographers’ camera lenses. These are the people who make a living with their equipment – and they frequently trust the Canon L Lens Series for their income.

About their L lenses, Canon says “these lenses use special optical technologies [such as] Ultra-low Dispersion UD glass, Super Low Dispersion glass, Fluorite elements, and Aspherical elements to truly push the optical envelope.”

OK so what does that mean – practically speaking?

What you can get when you use Canon L lenses (if you do your part right) are amazing pictures. In fact, this amazement is said to cause a disease know as “L-Disease”. Once caught, it is incurable. You will have to buy Canon L lenses in all of the focal lengths you use. AND you will be happy (and I hope you know that I am not being totally serious).

The EF 17-40mm f/4L USM is an ultra wide-angle zoom lens that offers excellent image quality and a constant maximum aperture. Its compact, lightweight body makes it an ideal travelling companion.

Features

 

  • Superb optical performance throughout the zoom range
  • Fast autofocus speed
  • Highly resistant to dust and moisture
  • 28cm minimum focusing distance at all focal lengths
A high-quality, wide-angle zoom for a variety of subjects.
Ultra-wide or standard zoom
The EF 17-40mm f/4L USM acts as an ultra-wide angle zoom on film or full-frame digital EOS cameras. On DSLRs equipped with APS-C sized sensors it acts as a standard zoom, giving an angle of view equivalent to a 28-70mm lens on a full-frame camera. 

Close focusing
Minimum focusing distance is just 28cm throughout the entire zoom range.

Superior optical performance
The EF17-40mm f/4L USM has 12 lens elements arranged in nine groups. Super Spectra coating ensures excellent colour balance and minimises ghosting and flare. To provide superb image quality over the complete 17-40mm zoom range the lens uses three aspheric elements. Super UD (Ultra-low Dispersion) glass prevents chromatic aberrations.

Ultrasonic focusing
A ring-type ultrasonic motor drives autofocus extremely quickly, and in near silence. Excellent holding torque ensures the point of focus is reached accurately, without overshooting. Furthermore, full-time manual override is available, making it possible to adjust focus without leaving AF mode.

Non-rotating front element
The front of the lens does not rotate, which makes using specialised filters, such as polarisers and graduates, easier. A drop-in gelatine-filter holder can be found at the back of the lens.

Smooth background blur
A virtually circular aperture diaphragm gives out of focus regions a softer, more uniform feel. Sharp foreground objects stand out against a smooth blurred background.

Weather resistant
Highly resistant to moisture and dust, the EF17-40mm f/4L USM is ideally suited for use in harsh environments. Environment friendly lead-free glass is used throughout its construction.

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