[Bermudamatt]

This is a really amateur question but I just have to know. I've used several other SLR cameras and on the lens is a switch that changes from AF to MF. On my Olympus E-510 lens I don't have that switch. Why?
Is it the llens switch better then no lens switch?

[matthew]

It depends on the type of focusing motor that the lens uses, and the way the focusing system is designed. The Olympus lenses have electronic focusing even when you're using manual focus; you turn the focus ring and the camera sends a command to the motor to shift the lens. This is why you can spin them quickly for a lot of movement or slowly for very precise minor changes -- even when you've moved the ring the same distance.

(There is a new system, similar to the USM/HSM/etc linear drive motors that Olympus calls "Supersonic Wave Drive", or SWD. These have mechanical focusing, losing the ability to set SAF+MF in the camera.)

[Bermudamatt]

So is one better then the other?

[matthew]

It's not really a question of better, it's just different. Everything's a compromise, it's just a question of whether you like the particular decisions the camera companies make. The ultrasonic/hypersonic/supersonic (linear) motors give faster and quieter focusing. A lot of people like the direct manual coupling as well. On the other hand, the focus-by-wire that Olympus uses allows free movement of the focusing ring -- you don't hit physical limits -- and there's never a chance that you'll damage the focusing mechanism by moving the ring when it's set to autofocus. You also won't have mismatched settings that cause the AF to 'inexplicably' stop working, and the focus ring doesn't move as the camera does its magic.

The focus-by-wire system that Olympus uses caused a lot of controversy when the E-1 was introduced, but the critics either were won over or wandered off after a couple of years. (The reality is that until Oly brought in Live View manual focusing with its cameras in particular and smaller-sensor DSLRs in general was a rather abstract concept.) It does give Olympus some neat abilities, like the hybrid MF+CAF system that the E-510 and E-3 share, but it's worth noting that now that they've developed (or found a way around the existing patents) their own linear drive motor they're starting to use it and moving away from their focus-by-wire system. They haven't said if they'll be updating any lens other than the 50-200, but two of their three newest new lenses are using it.

[shuttertalk]

Hey, the "electronic focusing" sounds like a pretty neat feature... didn't know that they did that.

On the Canons and Nikons, some of lenses have a FTM (full time manual) mode, where it autofocuses but you can override it by just turning the focus ring, without switching modes.

[Zig]

Fascinating; I never knew this about the Olympus.

[matthew]

I was browsing dpreview's lens test of the 14-42 "kit" standard zoom and was surprised to see a 'pro' comment of "Proper manual focus ring and non-rotating front element". I checked the main body of the review; they knew it was electronic but liked the way it was damped. From the review:

The most unusual feature of this lens's operation is the focus-by-wire manual focus system, which drives the focusing group indirectly via the lens's autofocus motor (as opposed to the direct mechanical connection found in most lenses). As a consequence, the feel of the manual focus ring never changes, regardless of whether the camera is set to auto or manual focus, or the focus has reached the limits of its travel (either close or infinity), and this lack of tactile feedback can be a little disconcerting in some situations.

(It's funny that out of context that reads as a negative, while the overall review makes it sound like a positive thing...)

Possibly the most sophisticated use of the focus-by-wire design comes when shooting with a combination of one of the highest-grade Olympus telephotos, continuous auto-focus, and manual focus with the latest generation of E-system bodies. The MF+CAF combination lets the photographer manually pre-focus the lens and hold that position before engaging the autofocus. (Older bodies needed to have the CAF active and 'tracking' a pre-selected point until the action started.) Any non-SWD lens can do that seamlessly, but the top lenses also have electronic focus-hold buttons around the barrel that temporarily halts the CAF. It's a system that lets the photographer take more control over the tracking of moving subjects. Hopefully Olympus will eventually come out with a bullet-proof predictive focusing system, but until then it's a useful ability.