The EF 300mm f/4L IS USM lens is a very popular long telephoto fixed lens among photographers who like their wildlife and sports images appear as sharp as possible, with rich color and contrast. It holds clear advantages vs the much more expensive Canon EF 300mm f/2.8L IS USM when you take its relatively lighter weight and smaller size into consideration. You can see the MTF charts for this lens and view a sample image at Canon USA.

You might like to quickly scan for available deals and best prices for the EF 300mm f/4L IS USM lens across multiple merchants here, here and here.

Collected here are links to various pieces of information on the Canon 300mm f/4L:

1. How well does the EF 300mm f4 L perform when used with a 1.4x teleconverter (TC)?
• Daniella shares a 100% crop of a bird photo shot with the EF 300mm F4 IS at F4.5 with a Tamron 1.4x TCM. The image was shot in JPEG mode, and Daniella thinks that sharp images are obtainable only if the lens is stopped down to f/5.6.
• The 300mm f4 IS lens is optically inferior to the non-IS version, and also produces images which are not as sharp as the EF 30mm f/2.8 IS USM lens.
• Why the EF 300mm f/4L might not be a suitable lens for bird photography.
• The farther away the subject is, the worse the quality of images from this lens.
• Greg claims that Daniella got a bad copy of the lens, and that images from a good copy of the 300mm f/4L would be better than those from the EF 100-400mm lens at 400mm focal length and f/5.6, but Daniella believes otherwise.
• Although these images are resized, Fred's closeups with this combination are simply superb - all shot in the range of f6.3 to f8.
• Really nice animal photos with a Canon EOS 5D by Melanie Kipp
• This resized bird photo is really good, considering that two 1.4x teleconverters were used with the 300mm f4L.
• 100% crop of a butterfly closeup shot with a Tamron 1.4x TC plus EF 300mm f/4L at f8, postprocessed.
• Gorgeous wildlife images from Gary Jean's portfolio
2. Bob Farmer summarizes his use of the EF 300mm f/4L IS USM (better for closeups) vs the Canon EF 400mm f/5.6L USM (more suitable for birding)