Understand the USM feature

So I thought that the difference between a USM and a non-USM lens is the fact that the USM is faster and quiet (please correct me if Im worng). But as I read through the forums, I see that people are saying that some of the USM lenes are slow to focus (70-300mm IS USM).
Does the USM have anything to do with the focusing speed of the camera? Im getting the 70-300 IS USM so I can have a nice zoom with a good price. But if the focusing is slow, then my purpose is defeated.

USM is simply the mechanism by which the lens focuses. It can yield faster focusing than a non USM lens (such as AFD or micromotor) but it's not a guarantee.

Generally the USM version of the lens focuses faster than the non-USM version. You can't compare two different focal length lenses for their focusing speed. I can tell you that my 70-300 USM is slow to focus. It is my slowest lens to focus in fact, but it is faster than the non-USM version of the 70-300. When people say a lens is slow to focus, they may be comparing it to the other lenses in their kit, which often isn't a fair comparison.

Also remember that lenses with larger apertures tend (there are some exceptions) to focus faster and better because the cameras (20D and up) use a cross hair on lenses 2.8 or faster.

There are also two types of USM, Ring (good) and Micro(Not as good).

In2Photos wrote in post #2162538
Also remember that lenses with larger apertures tend (there are some exceptions) to focus faster and better because the cameras (20D and up) use a cross hair on lenses 2.8 or faster.

There are also two types of USM, Ring (good) and Micro(Not as good).

Isnt the 70-300 IS USM a ring?

ChrisBlaze wrote in post #2162548
Isnt the 70-300 IS USM a ring?

No, the current 70-300 IS is micro-motor USM, not ring.

70-300 IS USM and the 75-300 IS USM are micro-USM type lenses, the focus ring does not have FT-M function. These lenses are slower to focus then most ring-type USM lenses. That said my 75-300 IS USM, isn't much slower then my 100mm f/2.8 Macro.

If you need a fast to focus AF tele, the 70-300 IS DO; 70-200mm f/4L; or the 100-300mm EF USM may be better choices.

For general use however, I find the speed of the 75-300 IS USM acceptable.

You can't fully appreciate a USM-equipped lens until you've gotten to experience the old AFD (Arc Form Drive) based lenses (e.g. the 50mm f/1.8 or 35mm f/2.0).

USM is fast and quiet by comparison!

As others have mentioned, there's more to the lens' AF mechanism than just the drive motor. On lenses like the 85mm f/1.2L for example, there's a lot of glass to move back and forth - slowing things down.

Double Negative wrote in post #2163321
You can't fully appreciate a USM-equipped lens until you've gotten to experience the old AFD (Arc Form Drive) based lenses (e.g. the 50mm f/1.8 or 35mm f/2.0).

USM is fast and quiet by comparison!

No doubt. I once bought an EF 50 f/2.5 macro on a whim. It was back in its box and on its way back to B&H the very same day it was delivered. USM only for me, thanks.

Double Negative wrote in post #2163321
You can't fully appreciate a USM-equipped lens until you've gotten to experience the old AFD (Arc Form Drive) based lenses (e.g. the 50mm f/1.8 or 35mm f/2.0).

USM is fast and quiet by comparison!

No kidding. I just got the 50mm f/1.8 about a month ago. I wanted to try a prime lens out and didn't want to front the money for a 50mm f/1.4 just to see if I would like prime lenses. I almost bust out laughing when I slapped it on my camera and heard it auto focusing. NEEEEEEEE CLUNK NEEEEEEEE CLUNK NEEEEEEEEEEEE! So used to my EF 28-135mm IS USM. After I put 28-135 back on I couldn't even tell if it was autofocusing unless I was looking through the lens. :P

MrChad wrote in post #2162728
For general use however, I find the speed of the 75-300 IS USM acceptable.

glad you are happy with it. the focus speed on that lens, espcially in low light drove me into the ground when i had it. it would take all day to find something, going back and forth back and forth, right past the subject multiple times.

John/Andrew...

LOL! That was my impression of the ol' 35mm f/2.0 when I first got it too (my first Canon AF lens, prime or otherwise). Bbbbbzzzzzt. Bbbbzzzzzzt. Bbbbbzzzzzt. The hideous AF mechanism of the D30 didn't help any!

Funny thing is, I still love that lens. I just happened to replace it with the 35mm f/1.4L a few weeks ago... I love the new one more.

who cares how loud the lens is? It takes fantastic photos and only costs 80 bucks!! I guarantee you a critic wont tell you that your photo sucks because the lens used to take it has a loud focus motor. Well... maybe some with a red L in their signature would The focus motor isnt the reason to spend $1,200 on a L lens.

I love my 35mm f/2 and 50mm f/1.8MK1. Both are fantastic pieces of glass and TOGETHER cost a fraction of what the 35mm f/1.4L or 50mm F/1.2L costs. Its something like 1/4

its obviously not loud enough to spook a wild deer!!

Date Taken: 2006-10-21 17:45:51
Model: Canon EOS DIGITAL REBEL XTi
Size: 3888x2592
Bytes: 6976817
Aperture: f/1.8
ISO: 400
Focal Length: 50mm (guess: 53mm in 35mm)
Exposure Time: 0.0012s (1/800)

sirsloop wrote in post #2163536
who cares how loud the lens is? It takes fantastic photos and only costs 80 bucks!! I guarantee you a critic wont tell you that your photo sucks because the lens used to take it has a loud focus motor. Well... maybe some with a red L in their signature would The focus motor isnt the reason to spend $1,200 on a L lens.

I love my 35mm f/2 and 50mm f/1.8MK1. Both are fantastic pieces of glass and TOGETHER cost a fraction of what the 35mm f/1.4L or 50mm F/1.2L costs. Its something like 1/4

Oh you won't get any arguement from me about not caring how loud the lens is. I still find it quite amusing though.

When I had mentioned that I was thinking about purchasing the 50mm f/1.8 around here I had soooooo many people tell me I was making a mistake and should get the 50mm f/1.4 USM. To the point that they were making it sound like it was going to be the biggest mistake of my life. I bought the 50mm f/1.8 and didn't look back. No regrets what so ever! It has become my favorite lens for shooting people with. So very sharp, and works really well along with my 580EX flash (the autofocus assist really improves things).

sirsloop wrote in post #2163536
who cares how loud the lens is? It takes fantastic photos and only costs 80 bucks!! I guarantee you a critic wont tell you that your photo sucks because the lens used to take it has a loud focus motor. Well... maybe some with a red L in their signature would The focus motor isnt the reason to spend $1,200 on a L lens.

I love my 35mm f/2 and 50mm f/1.8MK1. Both are fantastic pieces of glass and TOGETHER cost a fraction of what the 35mm f/1.4L or 50mm F/1.2L costs. Its something like 1/4

Couldn't agree more. Optically, both lenses are top-notch. Who cares about the buzz? Granted, it's not as fast to focus as USM but that doesn't matter if your subject isn't really moving too much.

I loved my f/2.0 so much that I upgraded - to the f1/4!