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EOS 450D - Auto Focus "Cross Type at F2.8 at center" er ... me no understandee (1 Viewer)

wilfredsdad

Well-known member
EOS 450D - Auto Focus "Cross Type at F2.8 at center" er ... me no understandee

Hello
Could somebody clarify this for me: looking at the spec of the EOS450D (which I am considering buying) it states that the auto focus system has 9 points and has a "cross type at F2.8 at centre"; the spec for the EOS1000D has "cross type at F5.6 at centre" - I'm not clear what this means and how significant it is when using a telephoto lens for bird photography. Does it mean that the centre focusing point only functions as a cross type (ie detecting focus on both the vertical and the horizontal axis) when the lens is set to the (big) apertures stated? At smaller apertures it only functions as a single axis focus point?
Is it absolute - ie it really won't work as a cross type focusing point on anything less than the apertures stated? or is Canon just playing safe and there is some latitude? Does it make a lot of difference with focusing speed, reliability, and accuracy?
There are two reasons why I am asking: 1)The problem I have with my current set up is that the camera (Olympus E510) often struggles to focus my Sigma 50-500 lens (it hunts for ever and I miss a lot of shots), and this is one of the reasons why I am considering upgrading my kit. 2)The EOS1000D centre point will work as a cross type at F5.6 (or so the spec says) and a 500mm lens that goes to F5.6 is going to be a lot more affordable than one that goes to F2.8.
The fact is that 90% of the time that I am photographing birds I am using the centre spot for focusing - so any improvement there might make a big difference (or maybe not 'real world' difference at all?)
Could anybody put me straight on this. Also - I am looking at the Sigma 150-500 lens to go with the EOS450D (or EOS 1000D) - anybody got any experience with that combination? particularly with regard to autofocusing efficiency and reliability. I am discovering that in bird photography focusing is more than half the battle - a very high percentage of the pictures I take (and it seems other people take) are useless because they are not quite in focus, regards Pete
 
Sorry that I cannot really answer your question, but here's a quote from another online review:

"Unlike the 40D, the slight upgrading of the 30D's AF system for the XSi doesn't include the addition of cross-type sensors at all nine points, with the system relying on single-axis sensors everywhere except the center (and then, if I'm interpreting Canon's literature correctly, only with f/2.8 or faster lenses). While debates rage about dual- versus single-axis sensors, I found the current implementation of Canon's nine-point system for its entry-level cams to be as quick and accurate in normal focusing situations as anything in this price class (including higher-spec AF systems from other manufacturers). With a fast-aperture USM lens, the setup is pure gold. You'll get the expected twitching and shaking with poorly damped consumer glass, but lock is still rock-solid reliable, even when using continuous drive for action shooting."

Personally, for close to the same cost, I would be looking at a 40D.
 
The center point is a cross point. If operates as a cross AF point for all EF and EF-S lenses. The center AF point provides enhanced focusing precision with lenses that have a maximum aperture of f/2.8 or more.

From what I can tell, the AF system on the 450D is the same system that was previously used on the 20D/30D. Autofocusing accuracy with a telephoto lens is more of a function of the tolerances of the lens and the body (as Canon's AF system is an open loop impementation), thus, if you really want the most accurate AF solution, you may want to get a 50D which supports per-lens AF micro-calibration so that you can tune your body to your specific copy of the lens.

Having said that, I was able to use the an EOS 350D with various telephoto lenses (Sigma 50-500mm, Canon 400mm f/5.6L) to get pretty decent results when shooting static subjects. However, the 40D does a much better job with Servo AF (moving subjects). I suspect the performance of 450D won't be far-off from a 30D/40D/50D.
 
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I do use the 450D,and it may be my imagination,but the center point (red AF dot) does not seem to be in the center.Does anyone else have this problem.Good little camera,takes sharp shots.
 
I do use the 450D,and it may be my imagination,but the center point (red AF dot) does not seem to be in the center.Does anyone else have this problem.Good little camera,takes sharp shots.

Christine, it sounds like you have a different focus point selected on your camera than the center point. Check your manual on how to move it to the center; it is a simple adjustment.
 
I do use the 450D,and it may be my imagination,but the center point (red AF dot) does not seem to be in the center.Does anyone else have this problem.Good little camera,takes sharp shots.

If you are wearing glasses, depending on the angle at which you are looking into the viewfinder, it is possible that you may not see the entire frame and therefore the center AF point may not appear to be in the center of the frame.
 
Macshark,yes,thanks,ou are quite correct.The center red dot does not seem to be in the dead center,seems to be over to the left,no I do not wear glasses when using the cam,so maybe need to change to a focus dot more to the right.
 
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