On aligning the lenses, yes a zoom lens is just as easy to do as a prime. The trouble is you can only adjust for one specific focal length. As Chuck has said the recommended way is to do it at the long end of the lens.
When lenses come from the factory they are typically aligned at only a couple of focal lengths. The Canon 24-70L originally was coming from the factory calibrated at 70mm but as time went on they now align it both at 70 and at 24. That leaves the rest untouched.
The theory is the alignment/calibration is done and built into the manufacturing process at the factory. The 24-70L lens has eight alignment points so taking the time to align that lens through all eight points and then making sure you haven't "undone" one of the other points as you move along can make for some interesting thoughts and would take a lot of time to do them all correctly. As Chuck said it will definitely be VERY interesting to see this feature develop as time goes on. As Canon looks for more bells and whistles to put into it's new cameras coming out - like the 1D(s) Mark VI this is one area where they can develop and it would be very appreciated by the photographers.
The thing about aligning a lens yourself is your ability to actually align the CAMERA to the "RULER. The gismo called the Lensalien deals with this by making you see a target through a hole and moving your camera around until you can see the target. When you finally can see the target it means the camera is in the right spot in terms of up and down and left and right. Think of it like being on one of those gun batteries on a war ship. The gun can move left and right and also up and down. To hit the target you have to be in the right spot on both axis'.
You can simulate this yourself without spending the money though. As I explained in the article - you level the camera and then raise and lower the tripod until your center focus point is over the big fat 0 on your target (in my case - the very large garden thermometer).
You can spend a hundred bucks to get this right, or take the time to level your camera and then lock in to your target using the tripod's controls. You will need to do this same thing with a purchased product anyway. I'll leave that call up to you
When you put your focus point over the 0 and your camera is level - you've done it correctly.
Back to zooms. If you calibrate for 70mm on a 24-70, or if you calibrate for 200 on a 70-200 and so on, this does NOT mean that the OTHER end is automatically goin be right. In fact, if you calibrate at 70mm and then conduct the test at 24mm and it is NOT in focus - your lens needs to go in to the service center for calibration as one end or the other is OUT of alignment and this is something you cannot control or fix yourself. It is an excellent way of testing your lenses to see if they really DO need to go in for service.
I just calibrated a 17-40L on a 1Ds Mark III camera. It was off by +14. On the wide side though it is harder to tell just because of the nature of the lens. I am getting MUCH sharper results now with it so the calibration was a success. My point is, it is worth taking the time and calibrating ALL your lenses. Take some time and set it aside and your rewards for doing it will be pretty good - plus it allows you to test your zooms to see for yourself if they are truly correct or not - no guess work involved.
Peter
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