Focus speed vs focus ability/camera focus vs lens focus

[timmyquest]

I hear about focus speed all the time but i'm confused as to which means which.

I know that when a camera focus speed is "high" it means that it can focus fast because of the math electronics etc inside the camera.

But when a lens focuses fast does it strictly mean the speed that the focus ring rotates, or do other lenses focus more efficianlty then others?

So can a lens both have fast ability and fast speed (if that makes since).

[wintoid]

I have 2 lenses, a 50mm 1.4 and a 24-85 zoom. The zoom seems to focus MUCH faster than the prime and almost never searches for the focus point. I don't know if this answers your question, but I thought I'd offer my impressions.

[KennyG]

Lens focus speed is 90% mechanical (the motor) and 10% electronic (communication with the camera).

If, like me, you are an action sports shooter, fast AF is essential. I wouldn't consider a lens without USM (or in Sigma's case, HSM) as the speed at which the lens adjusts means the difference between getting a shot in or out of focus.

The camera plays a part too and the new 1D MK-II has a very fast AF system, even better than its predecessor. The 1D is better than the 10D which is better than the D30, and so on. However, at the camera end it is how it decides on the focus point that is important and that is where the 1 series cameras really show there strengths. It is no good having an ultra fast AF system if it can't focus on the right spot.

[defordphoto]

Yes, usually when we speak of a fast lens it means a large aperture, or a lens that can take in more light. And then there's the AF speed. Canon makes both fast and slow AF lenses. Fast always means $$$ and you will pay for speed, whether it's aperture or AF.

For a camera to be ultimately ready to trigger the shutter relies on the camera talking to the lens, telling it to focus and where to focus, the lens responds, focuses and then reports back to the camera's CPU that it has focused. All in the meantime, the camera and lens are also talking back and forth about light.

Then your shutter actuates.

The 10D is probably considered "fair" as for AF speed. The 1D is good and the new MARK II is excellent. I know that once I get my MKII that I'll wonder how I got any shots of the cars and boats and other fast things that I shoot. ;)

[CyberDyneSystems]

The total speed at which a body lens combination will focus automatically is a combination fo the Camera's AF electronics and the Lens mechanics.

As RFM said,. the 10D/300D and there film counterparts,. the Elan series AF is pretty quick.. especially compared to ANY point and shoot.

The 1 Series is the top dog.. much faster and more robus.. better more accurate in low light... but you need to mount a lens that focuses fast to see the difference (as allways,. there is allways a bottleneck)

So a slow focusing lens like the 50mm f/1.8 will not seem much of any faster on a 1D when compared to the same lens on a 10D....

But whith a fast lens with a USM motor.. chances are the 1D series AF electronics will make that lens focus a lot faster (oh man does it ever!) :mrgreen:


When it comes to lenses and there own inherent AF speed... figuring out which will foucs faster is becomes quite confusing,.. there does not seem to be any rhyme or reason.

But there are some hard and fast rules.

Canon has "USM" or "Ultra Sonic Motor" focusing motors in there more pricey lenses.. there lenses focus much faster and quieter than there non USM counterparts..

Typically a lens that allows more light in will focus faster than a lens with a smaller aperture,. but this not a given.
The 85mm f/1.8 @ $350.00 focuses much faster than the $1400.00 85mmm f/1.2 L


Oddly, the 400mm f/5.6 L focuses faster than the 300mm f/4 IS L

Both lenses have USM.. the 300mm is shorter and has larger aperture,. it SHOULD focus faster, logically.. but it doesn't? Go figure. (perhaps the IS slows things down?)

Currently.. the absolute fastest Canon combo is the 300mm f/2.8 USM IS L mounted on a 1 Series Camera... this lens in particular has some added AF engineering applied that makes it Canons fasetest AF lens when coupled with the 1 bodies.. which is appropriare as the f/2.8 300mm is the long time favorite for pro sports shooters..


Another thing about the Cameras themselves..

the 7 point AF systems in the lower priced bodies include the ability to track to amoving sibject whaen all 7 focus points are activated in AI servo..

But the lack of focus point density makes this a very much hit and miss situation..

With my 10D I have had this function superbly tracking birds in flight in a few situations.. (against an empty sky for instance) .. but it's success rate,. after lots of practice is still only about 50% I'd say... if any clutter appears behind the subject,. the 7 AF points with all that space between them can get lost,. and start focusing on tress etc...

The first time I used the 1D with it's densely packed 45 AF points.. it was clear that this system REALLY WORKS with the 1 Cameras.. I was tracking gulls,. swans etc.. in front of the most cluttered backgrounds and the focus remained LOCKED on the birds. :shock:

I'd say after only one good day working with the 1D.. my succes rate was up around 95% keeping a bird in focus on the wing.. and this is with a Siga lens.. I have to assume that if I as using a Canon 500mm.. it would be even better.. as the two are more designed to work together.

[rodbunn]

There were just as many GREAT FAST shots before AF was around !!!
You can do it, turn of AF . . . Stop thinking you have to have "the best" to get great shots !!!

Member - Photographers Against Auto Focus (PAAF)


Ok, this is all in kidding . . . please NO E.MAILS

Rod

[CyberDyneSystems]

No Rod,. you are right really.. AF makes it a lot easier though :)

I know I'm not even remotely fast enough with manual focus to catch a moving target!

[rodbunn]

I'll never forget the first time I bought and used an AF body & lense...
I ran home and told my wife, this thing actually determined how fast
the player was moving toward me and tried to keep in focus !!!
She didn't care but I couldn't believe it. This was the best thing since sliced bread for a sports photographer (that's me thinking to myself)...

I depend on it A LOT, I just had to give ya'll a hard time :lol:

Take care, Rod

[timmyquest]

Compaired to all my other lenses my 1.8 is the fastest, and you guys call it slow!. I cant wait till i get some more canon lenses lol.