Canon UK now confirms that five of its lenses - including four telephoto models - won't be released as planned. While the firm doesn't address the earthquake in its prepared statement, a Canon France representative told French journalists earlier this month, at the Visa Pour l'Image press conference, that it expected operations in their factories to be restored to their pre-earthquake state by the end of June or early July.

The five lenses affected by the delay are the EF 300mm f/2.8L IS II USM, EF 400mm f/2.8L IS II USM, EF 8-15mm f/4L Fisheye USM, EF 500mm f/4L IS II USM and EF 600mm f/4L IS II USM.

The latter two - the 500mm and 600mm models - were expected to be released this summer. Now, Canon says they will appear "within 2011", adding that "any sales start dates will be communicated as soon as they become available."

The 300mm, 400mm and 8-15mm models are, on the other hand, suffering their second delay. The lenses were supposed to be released in January this year, but Canon was forced to postpone their availability "due to some adjustments in the manufacturing process."

Now, Canon expects the lenses to make it out of its factories in late July (for the 8-15mm model) and late August. "Canon would like to apologise to any customers who have been inconvenienced by these delays," the statement reads.

In an upcoming feature, to be published in BJP's June issue, David Kilpatrick says the delay doesn't come as a surprise. "Where regular interchangeable lenses can be mass-produced optically, even if hand-assembled for best quality, big fast lenses use glass elements of a size and composition that can only be produced in batches with a limited run," he writes. "Some, including the latest designs from Canon, use fluorite crystal instead of glass, despite its softness and fragility."

He adds: "The design cycle for lenses in the 300mm f/2.8 and above class involves a first computer and mechanical design, based on target values for the glass. The glass is then produced, and its refraction and dispersion figures measured. These will be very close to the target values, but hardly ever a perfect match. The design will be adjusted to compensate, including small changes to the curvature, thickness and spacing of individual elements. Both the elements and the mechanical parts of the lens body may be adjusted, using shims and spacers internally."

"Because of this, long fast lenses are released in batches, even if the assembly happens over a period of months or years," says Kilpatrick. "A hundred or thousand units of a particular complete set of elements may be produced. In the case of Zeiss, details have been released in the past showing that 100 units of production lenses will be backed up by 10 sets of glass held as repair components. Because the same glass cannot be repeated exactly, these high-end apochromatic telephotos can only be repaired while this stock lasts."

To read David Kilpatrick's complete guide of long fast lenses - from Canon, Nikon, Sigma, Olympus, Pentax and Sony - check out BJP's June issue on newsstands 01 June or subscribe to BJP.