II. LENSISSUES 23
AFSpeed According to
EFLens Vintage
EFExtender Issues
Justas EOS cameras have improved over time in terms of AF calculation speed, EF
lenseshave improved in terms of lens drive speed. Although most if not all EF lenses
regardlessof vintage autofocus quickly enough to satisfy the needs of photographers
who specialize in stationarysubjects, there is a significant improvement in lens drive
speed for fast-moving applicationssuch as sports photography when the newer lenses
are used with newer cameraslike the EOS-1 class digital SLRs.
Generallyspeaking, all USM lenses introduced since 1999, starting with the first 4
modelsin the IS (Image Stabilizer) super-telephoto series (300mm f/2.8L IS, 400mm
f/2.8LIS, 500mm f/4L IS and 600mm f/4L IS), autofocus noticeably faster than the
non-ISversions they replaced when used with an EOS-1 class digital SLR. Therefore, if
you wantto experience the maximum performance of your EOS-1 class digital SLR in
termsof AF speed, you must use a recent lens.
The technicalreason behind the improved performance lies in new programming on the
circuitboard in the lens that supplies an initial burst of electrical power to the USM
motor that’stwice as high compared to the older lenses. The USM motor takes
advantage ofthis extra power to focus the lens faster.
Allsingle focal length L-series lenses from 135mm to 1200mm plus several L-series
telephoto zoomsare compatible with Canon’s 1.4x and 2x EF Extenders. These
accessoriesare understandably popular among professional and advanced amateur
photographersbecause of the extra value they offer in terms of increased focal length
withoutforcing the photographer to invest in longer prime lenses.
Ofcourse, there are trade-offs for this convenience. The 1.4x and 2x Extenders cost1 or 2
f/stopsrespectively. This means, for example, that a 300mm f/2.8 lens when used with a
2xextender becomes a 600mm f/5.6. Additionally, EF Extenders reduce lens drive speed.
Asnoted in the instruction sheets supplied with the Extenders, the EF 1.4x or 1.4x II
reduceslens drive speed by approximately 50~67% depending on the lens in use. The EF
2xor 2x II reduces lens drive speed by up to approximately 75%. This speed reduction
givesthe AF system more time to detect focus. This is helpful since the depth of focus is
reduced with the longer effective focallength and the chance of defocus increases.
However, the reduced tracking speed and smaller maximum apertures(that sometimes
resultin the loss of cross-type sensor focus detection as mentioned in the description of
the 45-point Area AFSensor at the beginning of this document) caused by the use of
Extenderscan be a disadvantage with fast moving subjects, particularly in low light.
II. LENS ISSUES