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Old Nov 26, 2003, 6:41 PM   #1
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Default AF when zoomed?

I'm a hacker (at least thats what we call it in golf). Just got my 10d with canon EF 28-105 lens. While taking pictures in the "P" and "Auto" modes (all I've used) the camera tends to hunt and not lock with the lens zoomed. I can lock then zoom, but it seems like a waste. Of course I could focus manually but again I'm a hacker.

Is this normal?
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Old Nov 26, 2003, 10:37 PM   #2
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Interestingly enough, that lens is considered to not be very good optically, but it does have good AF motors.

What were you trying to take a picture of? You might want to look at this thread, I posted something about how AF works on most cameras, including the 10D.

http://www.stevesforums.com/phpBB2/v...ic.php?t=17217

Another thing to note is that the fstop at 105mm is f4.5. That means that the AF system gets less light than at 28mm. The more light you get, the eaiser it is for the AF systems to work (ignoring the issue of contrast, which I talk about in the other post.)

Eric
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Old Nov 27, 2003, 6:32 AM   #3
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Also
Quote:
I can lock then zoom
... while this was a good practice in the days of film cameras, newer low-priced AF zooms are bad at this, and relies on the continuous AF motor to keep focus. I have a famous EF lens that even its Canon's manual warns not to change zooming after the lens has locked focus (ie the focus point will change if the zoom position is varied)!
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Old Nov 27, 2003, 5:54 PM   #4
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Quote:
Originally Posted by eric s
Interestingly enough, that lens is considered to not be very good optically, but it does have good AF motors.


Eric
Ouch! The EF 28-105 lens is crappy? Does crappy mean it is not as good as a point and shoot? What lens would be better in this price range?
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Old Nov 27, 2003, 11:51 PM   #5
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I don't know how much you are looking to spend. So I'll do a little work for you. First I looked up the price of that lens at B&H Photo. They are the best reputable dealer in the US. You can buy cheaper some times, but not often.

That lens costs $219.95 there (all prices in my post are in US Dollars.)

Then I go to this web site and look at what they rate higher than that lens optically (while still keeping good AF performance.)

http://www.photozone.de/bindex2.html

Do you care if its a Canon lens or not?

The Canon 28-135 f/3.5-5.6 USM IS is optically a bit better, but has slower AF. Of course, the vast majoity of lenses have a slower AF than the other lens. But it costs twice as much @ $ 399.95.

The Sigma AF 28-70mm f/2.8 EX DF (I think NHL likes this one) is $ 299.00 and it's also good. Not the same reach as the other lens, though. But 100 cheaper.

Eric
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