Is it harder to focus..wide-open at f/2.8?

Joined
May 25, 2005
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I've seen comments from a few other shooters, about sometimes it's harder to get accurate focus at max aperture, particularly faster lenses? More shallow depth of field. Is this true?
I think maybe using a center AF point, would help. So would stopping down. But if I stop down enough, what's the point of an f/2.8?
 
Joined
May 3, 2005
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Yeah that's it. Depth of feild. This issue is why you see so much talk about the AF in various cameras and lenses. How fast and accurate debates, etc.

However a 2.8 ought to AF faster than a slower lens due to the greater amount of light reaching the camera. Also the 2.8 is more likely to be pro glass with AFS focusing. With moving subjects the real trick is to nail the focus plane. Many sports/PJ shooters pick a spot of focus and then wait for the player to enter that spot. I have done this, but not that often. A good camera and an AFS lens will get the job done most of the time. Also if you camera has the function you might try the group focus area. I did this recently with flying eagles and it worked very well.
 
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Mar 12, 2007
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I've seen comments from a few other shooters, about sometimes it's harder to get accurate focus at max aperture, particularly faster lenses? More shallow depth of field. Is this true?
Yes it's true. Well, it depends on what camera body you have. CAM 900 / 1000 bodies would be difficult especially if the lighting condition is bad or if the subject is moving fast but CAM 2000 bodies should have no problems focus tracking at f/2.8 aperture in those conditions.

I think maybe using a center AF point, would help. So would stopping down. But if I stop down enough, what's the point of an f/2.8?
Precisely. :smile: Stopping down gives you a larger DOF. So any "mistakes" from the camera AF or user error may be masked by the larger DOF.

Depending on what camera you use (how many cross type sensors), you may have to resort to the center AF point for more reliable focus. CAM 2000 bodies have 9 different AF points that you can manually select.
 
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May 3, 2005
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Stopping down in low light while shooting sports is simply not a very realistic option. You need all the speed you can get. 2.8 is not even enough in many gyms.

You need AFS and cam 2000.

It can be done with less, but your keeper rate will suffer.
 
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Huntsville/Muscle Shoals, AL
I didn't miss focus very often this football season shooting the D2H at f/2.8. I have a D200 now as well, and I am pretty sure that I can tell a difference...not a great one, but enough that at 2.8 shooting continuous, that at 2.8 the DOF was shallow enough that if your focus didn’t keep up you would loose shots. I have had the D2H loaned out for a couple of months, and can’t wait to get it back because compared to the D200 the D2H seems to make focusing “easy”, if you will.
 
Joined
May 11, 2006
Messages
41,172
I've seen comments from a few other shooters, about sometimes it's harder to get accurate focus at max aperture, particularly faster lenses? More shallow depth of field. Is this true?
I think maybe using a center AF point, would help. So would stopping down. But if I stop down enough, what's the point of an f/2.8?
imo no
you either hit it or you don't
now things beside and behind the hit may not be in focus at 2.8 vs say f4
use NC and chk image focus pt
 

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