Making sense of the STM lenses and the 650d AF

I decided to create a new thread because I notice that there is a big misconception of what the new hybrid sensor in the 650d and the new STM lenses. Here are the main points:

• STM lenses are not new mounts nor are they intend to supplant existing EF/EF-s lenses. The electronics of the EF is still the same, and the latest in optical design and IS and coatings are still employed. Only the motor changed.

• STM lenses are to complement existing EF and EF-s lenses. They are additions to the Canon lens lineup to address those who do lots of video.

• STM lenses are more specific to video shooting because:

1. They don't jerk/snap focus abruptly in video mode as with other motors
2. They AF smoother in achieving focus so that is not jarring to the shoot

3. There is also a less tendency to overshoot the subject of AF and hunt noticeably before focus is achieved

4. They are supposed to be quiet too, so that you will pick up less noise as you focus with STM.

• STM lenses tend to achieve focus better in video mode in that they work well in fine increment adjustments. They are also less taxing to the motors compared to other designs that may actually prolong your lens motors life if you shoot a lot of video and use AF in the process.

• USM motors will still be faster than STM and more advantages for pure stills shooting.

• You can still use your old EF and EF-s lenses with the 650d.

• Think how stupid Canon can be if it is to use only the 40mm f2.8 and the 18-135 STM lenses on the 650d and be denied of the use of the excellent EF and EF-s lens lineup built for over 20 years! Would you buy the 650d if you have only these two lenses to use? Think about it!

• Think of how silly it is too if you build STM lenses and you can't use it with your older camera bodies. Yes, Virginia, you can use STM lenses in your earlier EOS bodies.

• Nobody is forcing anyone to buy STM lenses. They are additions to the lineup. No any different if they made a 17-50 f2.8 IS vs the kit lens.

• You can use the new STM lenses with your older camera bodies

• If you do, it does not mean you suddenly have a faster AF. The older body such as th 600d or 500d or 550d will still focus poorly with the new STM lenses. That fast AF is due to the hybrid cmos sensor of the 650d. You have to have that sensor to get this fast AF in video or liveview.

• If you use the 650d with older USM lenses, now they will focus rather quickly in liveview and video (how quick is for future tests, but for sure, it's not a 1-2 second wait anymore). But then again, you will likley get a jarring snap focus or have that hunting in your footage as the USM motors are not optimize for video shooting. Silent as USM are, they may still have sound that can be picked up by the camera mike. The IS might also be noiser in the older non STM lenses. A source of irritation for those who do video.

• The 650d is not the replacement of the 600d according to a European Canon rep/spokesman. It sits between the 600d and the 60d. I disagree with this, but then again, that is what their rep said. If this is true, then the 600d will sold in tandem with the 650d for the foreseeable future.

The 650d is a preview of the future of Canon MILCs, and 60d and 7d replacements. And 3 years down the road, expect the 5d mk4 and future 1Dx's to sport the same hybrid AF/sensor. I won't be surprised if they use it in their higher end P&S either in their succeeding releases.

In any case, I hope the misconception about what STM lenses and what the 650d is put aside so that discussion will move along on how the camera and lenses actually peforms vs the 600d, 60d and other camera brands such as Nikon.