To follow up on this and clarify my own earlier post so subsequent readers aren't confused: the situations I described using my xsi at less than f5.6 were low contrast and often low light (since I was using flash, thus not worried about available ambient) - THAT will be why the lenses hunted, not because the aperture itself caused a problem.
Regardless of the reasons, the 7d's vastly increased AF sensitivity, speed and accuracy in those same conditions is significant, which was the point I was making I amended my earlier post to reflect this.
Thanks for the further tech-splanations, Ziggy & Co!
Thanks Bluemore and Ziggy, that confirms what I thought. My guess is that when you have an image that is barely good enough to focus on it's pretty hard to it's pretty hard to set up a consistent tests to use to make comparisons.
Here is how autofocus and stopping down works...yes the lens is always focusing at max aperture, the caveat is that it is the max aperture FOR the selected focal length. So if you are using a 3.5 (@WA)-5.6(@fullzoom) lens zoomed in, you are focusing at f5.6 as that is the max aperture for the focal length. Unfortunately you can't focus at f3.5 on the long end if all ya got is 5.6.
That's a really good point when considering the value of constant-aperture zooms like the 17-55 and 24-105L. They cost a lot more, but they do bring this important advantage in focusing performance as well as simply being faster at the long end. Constant aperture is a feature not enough people talk about, but a zoom without it is much more challenging to use.
Also, if I remember correctly, the 7D high precision autofocus in low light needs a max aperture of f/2.8 or wider, which gives lenses like the 17-55 f/2.8 an advantage with the 7D in low light.
Enjoying this conversation but wonder if anyone has a link to a "real life" type tutorial on the various AF functions of the 7d? We LOVE our new 7d but we know we aren't using the focusing system to it's greatest potential... we're just "scared" to play around with it!
Las Vegas Wedding, Family, and Special Event Photographers.
Canon 7d
2 Canon 40d
70-200 f2.8L IS, 50mm f1.4, 50mm f1.8, 28mm f1.8, Tamron 17-55 f2.8, ProOptic 8mm Fisheye
And a bunch of other stuff
Enjoying this conversation but wonder if anyone has a link to a "real life" type tutorial on the various AF functions of the 7d? We LOVE our new 7d but we know we aren't using the focusing system to it's greatest potential... we're just "scared" to play around with it!
You can always reset the camera to factory standards if needed or if you forget all that you have changed. Feel free to experiment, just don't experiment during a critical or paying gig.
Start with this Canon explanation of the different AF capabilities and functions:
I think I may be misunderstanding something about how autofocus works. I thought auto focusing is always done with the lens wide open, then it stops down to the selected aperature when you release the shutter. So I guess what I don't understand is why the aperature setting would affect how long it takes to focus? Does the camera do some kind of final focus check at the selected aperature?
No. You're right.
However there are 2 scenarios where you would focus at the set aperture. One is you're using a lens with a manual aperture ring (mainly older mechanical lenses, but some electronic lenses have it too with an override). The other situation is that some cameras do have a depth of field option so you can view and focus your shot with the set aperture enabled, but this mode is never a default setting.
No matter what the AF mode is, the less light the harder it gets for any camera, which is what happens when you stop down obviously... so I'd say the case isn't that the camera does a secondary focus check.
in my opinion you shouldn"t buy 7d why?
beacuse you already have crop sensor camera and now that"s good time to move to full frame camera like 5d markll and you can use your 50d for your backup.
but anyway 7d that"s best cop camera
canon EOS 7D /canon 5d mark ll/ EF 70-200mm f/2.8L IS II USM/EF-S 10-22mm f/3.5-4.5 USM/ canon lens 85mm 1.8
Well, here's an update about my 7D.
When I first got it I noticed that the camera took soft images. I did some research and I also asked around here and other places about what might be the cause. Nothing changed.
I sent the camera in and sure enough the AF system was not functioning properly and needed to be repaired.
Just got it back. Seems to be working well now.
R.
Canon 5DMk II | 70-200mm f2.8 IS USM | 24-105mm f4.0 IS USM | 85mm f1.8 prime.
Well, here's an update about my 7D.
When I first got it I noticed that the camera took soft images. I did some research and I also asked around here and other places about what might be the cause. Nothing changed.
I sent the camera in and sure enough the AF system was not functioning properly and needed to be repaired.
Just got it back. Seems to be working well now.
R.
that is good to know. My son bought one and had a similar problem. He returned it and bought the 5d mii
Comments
Regardless of the reasons, the 7d's vastly increased AF sensitivity, speed and accuracy in those same conditions is significant, which was the point I was making
Thanks for the further tech-splanations, Ziggy & Co!
http://www.danalphotos.com
http://www.pluralsight.com
http://twitter.com/d114
That's a really good point when considering the value of constant-aperture zooms like the 17-55 and 24-105L. They cost a lot more, but they do bring this important advantage in focusing performance as well as simply being faster at the long end. Constant aperture is a feature not enough people talk about, but a zoom without it is much more challenging to use.
Also, if I remember correctly, the 7D high precision autofocus in low light needs a max aperture of f/2.8 or wider, which gives lenses like the 17-55 f/2.8 an advantage with the 7D in low light.
Canon 7d
2 Canon 40d
70-200 f2.8L IS, 50mm f1.4, 50mm f1.8, 28mm f1.8, Tamron 17-55 f2.8, ProOptic 8mm Fisheye
And a bunch of other stuff
You can always reset the camera to factory standards if needed or if you forget all that you have changed. Feel free to experiment, just don't experiment during a critical or paying gig.
Start with this Canon explanation of the different AF capabilities and functions:
http://www.usa.canon.com/dlc/controller?act=GetArticleAct&articleID=3049
Also the Canon video tutorials here:
http://www.usa.canon.com/dlc/controller?act=GetArticleAct&articleID=3167
Feel free to ask any questions you might come up with back here. More than likely someone will jump in with an answer pretty quickly.
Moderator of the Cameras and Accessories forums
No. You're right.
However there are 2 scenarios where you would focus at the set aperture. One is you're using a lens with a manual aperture ring (mainly older mechanical lenses, but some electronic lenses have it too with an override). The other situation is that some cameras do have a depth of field option so you can view and focus your shot with the set aperture enabled, but this mode is never a default setting.
No matter what the AF mode is, the less light the harder it gets for any camera, which is what happens when you stop down obviously... so I'd say the case isn't that the camera does a secondary focus check.
why?
Las Cruces Photographer / Las Cruces Wedding Photographer
Other site
beacuse you already have crop sensor camera and now that"s good time to move to full frame camera like 5d markll and you can use your 50d for your backup.
but anyway 7d that"s best cop camera
When I first got it I noticed that the camera took soft images. I did some research and I also asked around here and other places about what might be the cause. Nothing changed.
I sent the camera in and sure enough the AF system was not functioning properly and needed to be repaired.
Just got it back. Seems to be working well now.
R.
Las Cruces Photographer / Las Cruces Wedding Photographer
Other site
Fantastic.
Moderator of the Cameras and Accessories forums