what are the fastest-focussing canon lenses out there?

[wickerprints]

The AF speed of a lens depends on multiple factors:

1. The body used: 1D-series bodies process AF information faster than lower-end bodies, and therefore the focus adjustment is more responsive.
2. The size and type of the AF motor. USM is faster than non-USM, and the larger the USM diameter, the more power it has.
3. The size and weight of the focusing group. Lenses with heavy focusing groups tend to be more slow to focus, since the motor must work harder to move those elements.
4. The sensitivity of focus to the movement of the focusing group. Lenses that have a short travel are faster to AF, but are also less precise, because the stepping increment is larger relative to the length of the helical.
5. Lighting conditions: some lens/body combinations are faster to focus in low light than other combinations.

Thus, the EF 85/1.2L design is a slow-focusing lens because, although it is the only lens besides the 200/2L, 300/2.8L, and fast supertelephoto primes to employ Canon's largest-diameter 77mm USM, the optical design is such that focusing is achieved by moving all elements excluding the rearmost. Even the EMD is moved. It has one of the most power-demanding requirements of any EF lens.


The EF 100/2.8L macro IS is an example of a lens that can focus quickly or slowly, depending on how it is used. This is because the lens is designed so that most of its focusing helical is devoted to subject distances less than 1 meter, and only a very small portion is reserved for 1m - infinity. So if your subject is close, focusing can be slow; if your subject is distant, focusing can be very fast. This is intentional, of course, because it is a macro lens. The use of the focusing limiter switch is one way to improve AF speed.


The fast supertelephoto primes are fast-focusing because they have a large USM and the focusing group is small and relatively lightweight, without a complex floating design that is found in zoom designs.

[HDNitehawk]

While the suretele

[memostothefuture]

first off: I always love the high quality answers I get here. thank you all for that.


rich, I have the 70-200 f2.8 LII IS as well - is the 24-70 as fast? (that would be great imho.)


jan and wickerprints, I appreciate your advice on the bodies. not sure if my immediate budget will allow for an upgrade but it finally explains to me why I should invest in those bodies when up until now the 7D seemed fine to me. (image size didn

[Richard Lane]

first off: I always love the high quality answers I get here. thank you all for that.


rich, I have the 70-200 f2.8 LII IS as well - is the 24-70 as fast? (that would be great imho.)


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<span style="font-size: 10px;"]<span style="font-size: small;"]Memos to the future..., <span style="font-size: small;"]It's our pleasure!


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<span style="font-size: small;"]I just tested the 24-70mm f/2.8L macro and compared it's AF speed to the 70-200mm f/2.8L IS II. I used my 7D in one shot<span style="font-size: small;"]so I could hear the "beep and be more aware when AF lock was achieved.


<span style="font-size: small;"]<span style="font-size: small;"]I can't really tell much of a diifference in AF speed, maybe the 24-70mm f/2.8L feels a little faster due to it's shorter focal length.


<span style="font-size: small;"]As a reference, I also compared both to a 135mm f/2L and they all seemed very fast. If I had to choose a winner, I would give the nod to the 135mm f/2L, not surprising because it's a prime and f/2.


<span style="font-size: small;"]They all appear to be "very fast and instantaneous" to me.


<span style="font-size: small;"]I also tried them all in AI Servo and they all felt very fast.


<span style="font-size: small;"]Just be aware, as mentioned above that the 24-70mm f/2.8L Macro, has a macro range that you should stay out of.


<span style="font-size: small;"]I hope that helps,


<span style="font-size: small;"]Rich

[iso79]

You guys also forgot the 35mm f/1.4 L.