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Old Mar 26, 2004, 7:46 PM   #1
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Default Tokina AT-X 287 AF Pro SV

I bought this lens (the 28-70 mm variant) for my 300D, and I must say I'm very pleased with the image quality and versatility of the unit. It's also made very well. That said...

This is one of the lenses with the "focus clutch" as well as the AF/MF switch. Both the instructions and the market-droid description of the lens in various publications indicate that you switch from auto to manual focus by pulling the focus ring back toward the mount, disengaging the motor/gear stuff from the focus hardware -- and that using the AF/MF switch is optional.

But when I pull the ring back into the "manual" slot, the motor is obviously still connected. It zizzes and tugs at me while I focus the lens. Only turning the switch to "MF" frees the focus ring and allows smooth focusing. Likewise, switching to "MF" while the lens is in the autofocus position only disables autofocus and prevents manual focus -- that is, turning the ring does nothing at all.

So is the manual just poorly written and/or seriously misleading? It's kind of bizarre that I have to pull the ring and throw the switch to go to manual, and then push the ring/throw the switch again to go to auto, but that's the way mine actually works...
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Old Mar 30, 2004, 9:21 AM   #2
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I have a similar experience when I use my Tamron 70-210, it sounds like it has a similar slide.

I think your lens is working correctly, my slide allows you to manually focus while the camera is in AF mode. Essentially it focuses then I can tweak focus if need be. The MF/AF switch totally disengages the AF.

Your camera is trying to refocus, I never use the all points focus, just the centre spot. When I do this it doesn't hunt too much.

As too why you need to pull the ring back too manual focus - that seems odd.

As an aside - I think one of the benefits of buying Canon gear is that the instructions are clearer. If/when I buy a bigger flash I'm going to plunk down the extra money and get the 550EX not the Sigma just for the manual. For my prime lenses I'll continue to buy based on value, the Canon instructions are pretty skimpy at times and they're pretty simple devices.
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Old Mar 30, 2004, 9:54 AM   #3
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Apparently the focusing hardware inside the lens is designed to physically decouple from the ring when you push the focus ring forward; there's a hash mark on the lens body labeled "manual" and one marked "auto" so you can see what position it's in. That much is clear in the docs; but it seems to indicate that you can focus the lens in "auto" without throwing the little AF/MF switch. That's very difficult, because with the AF turned on and the ring pulled back (still coupled to the focus mechanism), it fights every motion of the ring, and has lots of backlash. I've noticed that it doesn't autofocus very well, either, due to the added friction.

With the lens ring forward, the lens cannot be focused manually no matter what position the AF/MF switch is on, so it really needs to be set to AF. With the switch in "MF" and the ring pulled back, manual focusing is very smooth. The other two combinations of positions (forward/MF and back/AF) are pretty much non-functional. I guess this is why people spend money to get FTM on the real Canon lenses.

More an annoyance than a real problem, though; the lens is fast (f/2.8) and sharp enough for me. I did some RAW mode shots over the weekend, and 100% magnifications look very good. And it has a great feel. I just have to remember to perform two actions when I switch modes...
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