I'm interested to know where the max aperture changes for the EF 100-400/4.5-5.6L IS. Specifically I want to know whether it's a 300/4.5 or a 300/5.6 or something in between. I'm trying to weigh the zoom convenience against the (slightly) lower cost and (slightly?) higher quality of a 300/4 IS with(out) 1.4x tc.

The Canon website helpfully mentions that the max aperture is printed on the lens barrel (presumably the part that's exposed by the push/pull zoom). Unfortunately no one ever seems to have any in stock to play with.

-- Ben Jackson (ben@ben.com), July 05, 1999

Answers

Pop Photography (Feb 99) report it as a 100/4.5, 200/4.5, 300/5.6 and 400/5.6, so it looks like it goes from 4.5 to 5.6 somewhere between 200mm and 300mm. Of course they may be working in 1/2 stop steps. If you have an EOS-1(n) or EOS-3 which work in 1/3 stop steps you might get back 1/3 stop at 300mm.

-- Bob Atkins (bobatkins@hotmail.com), July 05, 1999.

When Photodo runs MTF tests on a zoom lens, they report its maximum aperture at each tested focal length. Surf to http://photodo.com and click on "Lens" near the top of the home page, then persevere until you bring up the right lens review.

-- Michael Lopez (mlopez@econ.ag.gov), August 10, 1999.