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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 21 Oct 2012 (Sunday) 06:39
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7D Focus :-) Why did this happen?

 
ljason8eg
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Oct 21, 2012 18:37 |  #16

That's the parallax effect for sure.


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jase1125
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Oct 21, 2012 18:57 |  #17

One other thing OP... You setting of F5.6 does not impact how the AF points are used. When the camera focuses, it always uses the largest aperture of the attached lens. For example, your lens focused using F1.8 and then stopped down at your setting of F5.6 when the frame was snapped (if you were using the nifty fifty). Set your aperture based on how you want the pic to look. Your aperture setting does not impact af performance .


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Arte ­ Automobilistica
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Oct 22, 2012 03:27 |  #18

jase1125 wrote in post #15151389 (external link)
One other thing OP... You setting of F5.6 does not impact how the AF points are used. When the camera focuses, it always uses the largest aperture of the attached lens. For example, your lens focused using F1.8 and then stopped down at your setting of F5.6 when the frame was snapped (if you were using the nifty fifty). Set your aperture based on how you want the pic to look. Your aperture setting does not impact af performance .

Now that is interesting and good news :D. I thought I had to actually use a max of 2.8 (for the centre) or 5.6 (for the outer) based on what I found on the Canon website:

"The actual AF system in the EOS 7D is entirely new to the Canon line, with an AF sensor having 19 cross-type AF points. Each and every point, including those located farthest from the center, is a standard-precision cross-type sensor, which can be used with any lens (or lens plus extender combination) with effective maximum apertures of f/5.6 or faster. Like the EOS 60D and 50D before that, the center AF point also has a separate, diagonal pair of high-precision line sensors, which provide even greater precision; these are automatically used with lenses f/2.8 or faster."


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Lowner
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Oct 22, 2012 03:37 |  #19

Arte Automobilistica wrote in post #15152914 (external link)
Now that is interesting and good news :D. I thought I had to actually use a max of 2.8 (for the centre) or 5.6 (for the outer) based on what I found on the Canon website:

"The actual AF system in the EOS 7D is entirely new to the Canon line, with an AF sensor having 19 cross-type AF points. Each and every point, including those located farthest from the center, is a standard-precision cross-type sensor, which can be used with any lens (or lens plus extender combination) with effective maximum apertures of f/5.6 or faster. Like the EOS 60D and 50D before that, the center AF point also has a separate, diagonal pair of high-precision line sensors, which provide even greater precision; these are automatically used with lenses f/2.8 or faster."

The camera only stops down to your chosen aperture for the exposure, before and after it is using the maximum aperture the lens is capable of, so an f/2.8 lens will use that, closing to f/5.6 only very briefly for the capture before reopening.


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apersson850
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Oct 22, 2012 03:55 |  #20

Arte Automobilistica wrote in post #15152914 (external link)
...with effective maximum apertures of f/5.6 or faster.

That's the key. It says maximum aperture, not used aperture.


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philwillmedia
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Oct 22, 2012 04:28 |  #21

ljason8eg wrote in post #15151307 (external link)
That's the parallax effect for sure.

Agreed...
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Here is the best explanation of it, complete with diagrams...
http://photography-on-the.net/forum/showthre​ad.php?t=487139


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Oct 22, 2012 08:13 |  #22

Images from DCFan and Alan both use narrow apertures with subsequent large depth of field and, therefore, minimal panning effect. And in these style of shots you don't need a wide aperture to blur the background - the panning will do that for you.


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Oct 22, 2012 11:46 |  #23

Arte Automobilistica wrote in post #15152914 (external link)
Now that is interesting and good news :D. I thought I had to actually use a max of 2.8 (for the centre) or 5.6 (for the outer) based on what I found on the Canon website:

"The actual AF system in the EOS 7D is entirely new to the Canon line, with an AF sensor having 19 cross-type AF points. Each and every point, including those located farthest from the center, is a standard-precision cross-type sensor, which can be used with any lens (or lens plus extender combination) with effective maximum apertures of f/5.6 or faster. Like the EOS 60D and 50D before that, the center AF point also has a separate, diagonal pair of high-precision line sensors, which provide even greater precision; these are automatically used with lenses f/2.8 or faster."

Key words here in bold.


Mark

  
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Poe
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Oct 24, 2012 20:32 |  #24

FrayAdjacent wrote in post #15150029 (external link)
Looks like it caught focus on the rear driver's side roll cage, which is a bit far from the front passenger fender.

Looks like you and I are the only two who looked at the photo critically. If this was motion blur, the roll cage should be blurry too, but it isn't. The pan stopped the motion in the focus plane, but the focus plane was not in alignment with the green badge on the car, it was on the roll cage.



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Bill ­ Boehme
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Oct 25, 2012 00:32 |  #25

Poe wrote in post #15165628 (external link)
Looks like you and I are the only two who looked at the photo critically. If this was motion blur, the roll cage should be blurry too, but it isn't. The pan stopped the motion in the focus plane, but the focus plane was not in alignment with the green badge on the car, it was on the roll cage.

I think it is possible that others also did and came to different conclusions.

One thing that is a bit problematic with your assumption is the DoF at the aperture and FL of the shot which is quite deep -- far greater than needed to assure that all of the car is in focus even if the focus was at the back bumper.

It is possible that the motion blur is entirely in the subject and not the camera. A close examination of the blur at the leading edge of the auto shows that the blur is directional so it can't possibly be all focus blur. So what could cause the front to be blurred by apparent motion blur and possibly some focus blur? One thought is that there might be some front end bounce from either a slight dip or hump in the roadway -- another cause of the front end blur could be from hard acceleration (or braking).

You mentioned the roll cage appearing sharp. I also had looked at that and notice that the vertical parts of the window frames showed some motion blur in the direction of travel. The bars in the roll cage are primarily along the horizontal axis with not much vertical component. Downsizing and sharpening the image may have obscured much evidence here. Further, the interior of the auto is rather dark so faint blur does not manifest itself very clearly in that situation because of reduced resolution in luminance levels. Another reason that I might throw out for less blur in the roll cage is that the camera seems to be tilted about 8° clockwise unless the track has a significant uphill slope. Could it be that while panning, the OP was also rolling the camera about the LOS (line of sight)? Nobody knows for certain, but that could also cause blur in the image.

Resizing the object also has an effect of suppressing blur when it is below a threshold. Additionally, most resizing algorithms employ sharpening (with no option to turn it off) which also will suppress blur.

My viewpoint is that there is not enough information in a downsized image such as this to say much with certainty. I do not see any clear-cut explanation for any theory, but plenty of room for postulating. The bottom line is that there does not appear to be any camera problem and this is nothing more than one of those shots which we all get that needs to go in the bit bucket and not worry about the cause (unless it becomes a persistent problem).

For the OP, I would offer some thoughts:

If your goal is to show motion blur in the background while the car is sharp, I would do several things. First use a medium telephoto lens of 100 mm FL or longer. Use a smaller aperture to make certain that the car is in reasonable focus. Use a higher ISO -- don't be afraid to use high ISO with the 7D. Finally, use a faster shutter. The longer lens FL will provide the necessary background blur while the faster shutter will minimize subject blur.

If your intent is to convey a sense of speed, a different approach that you might consider would be not panning, but instead have the camera sitting still on a tripod, use a shorter FL lens, perhaps an even slower shutter, a small aperture so that everything is in focus (as in hyperfocal), and higher ISO. You may have seen this approach used for photographing sports like downhill skiing and sprints.


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kfreels
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Oct 25, 2012 01:48 |  #26

I'm not going to weigh in on whether it is motion blur or just missed focus. It's really difficult to tell for sure. I'll just pass on some useful information on how the sensors on the 7D tend to grab onto contrast outside the actual AF focus point - especially when there is a lack of contrast within.

http://blogs.stonestep​s.ca/showpost.aspx?pid​=54 (external link)

I'm convinced that the enhanced sensitivity and the way the AF sensor works outside the actual AF point is why so many people have trouble with the 7D focus. Once you understand in detail how it works, it's easy to deal with.


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7D Focus :-) Why did this happen?
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