The 14 L II ships with a Canon LP1016 lens pouch. For better protection, consider the Lowepro Lens Case 1W. This lens is not compatible with extension tubes or Canon's 1.4x and 2.0x extenders.
The 14 L II's MFD (Minimum Focus Distance) is .7' (.2m) for a .15x MM (Maximum Magnification). This is plenty close enough for dramatic perspective distortion, but this is not a high magnification value. Even with a close subject, you need an interesting wide background for a pleasing shot.
Pictured above from left to right are the Canon EF 15mm f/2.8 Fisheye Lens, Canon EF 14mm f/2.8L USM Lens, Canon EF 14mm f/2.8L II USM Lens, Canon EF 16-35mm f/2.8L II USM Lensand Canon EF-S 10-22mm f/3.5-4.5 USM Lens. Below are the same lenses (sans the 14mm L I) with their lenses hoods in place.
The 16-35mm II and 14 II are similarly sharp in the center, but the 14mm II has the edge at the corners. Both lenses have a similar amount of flare overall - though the flare is different in appearance as could be expected. The 16-35mm II has more barrel distortion. The 16-35mm II has a sharper light fall-off contour - it is not as smooth (better for cropped cameras). The 16-35mm II has more CA in the corners. The 16-35mm II meters 1/3 stop brighter. The 16-35mm II can take front-mount filters - and with such is better weather sealed. The 14mm II is wider, but the 16-35 II offers more versatility. The 14mm II is smaller (much smaller in comparison with hoods) but more expensive.
The only Canon EF Lenses wider than the Canon EF 14mm f/2.8L II USM Lens are the Canon 15mm f/2.8 Fisheye Lens and Canon 8-15mm f/f/4 L USM Fisheye Lens. The above examples are from a 1.3x FOVCF lens. Here is a full frame (Canon EOS 1Ds Mark III) focal length comparison.
I think you will find the following sample crop comparison useful. Use the mouseover feature on the following list of lenses
to display the 100% crop from that particular lens.
Those with an EF-S compatible EOS camera body have another option for their super-wide angle lens - the Canon EF-S 10-22mm f/3.5-4.5 USM Lens. While its varying aperture never gets as wide as the 14mm II's, the EF-S 10-22mm's focal length range goes much wider and is far more versatile. Use the mouseover below this picture to see the 10mm vs. 14mm difference ...
Mid - frame
* LENS FLARE
* LENS DISTORTION