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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 15 Jul 2009 (Wednesday) 08:41
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Canon 5DMKII: AF Questions, Thanks

 
TexRex
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Jul 15, 2009 08:41 |  #1

Still getting used to Canon after the switch from a D700 but got a couple question's if anyone can help. THE AF system is definately differrent from my D700. Both have their pros and cons imo but this 9 pt system is a bit differrent. 5DMK2 BTW.

1) In regards to the AF system If I am using a f/2.8 or faster lens is it optimal to use the center focus points and the invisible assist point directly on top and below the center point all within the center focus circle? Also if I am shooting vertical with my grip I would use the center focus point and then the invisible AF assist point to the left and right of the center focus point?

2) Since the center focus point is the "optimal" so I hear, in order to get the sharpest shots without always having your subject in the center is to focus from the center point and then recompose and frame differently (still same distance though)?

3) When using AI Servo mode do you Canon users use the Center focus point to hit your subject with and then while they move just keep your subject while moving somehow within that center circle hit by the center point and the 6 invisible assist points? Or do yall use all the AF points in AI Servo?

4) On my D700 and pretty much all the Nikon's, there is an AF assist illuminator next to the lens mount. On the 5DMK2 there is not one. I have the 580exII speedlight which has the AF assist beam. Is there a way to use the AF assist without firing the flash in low light situations?


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MarkV
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Jul 15, 2009 09:26 |  #2

I'm no expert on matters of proper AF technique, but I have found that using multiple focus points has yielded inconsistent results in my photography. I use the center point only, focus on my subject and recompose if the subject isn't in the center of the frame. It is definitely a slower method of photography, and may not suit all styles (animals, kids, or anything else that moves "randomly" could be a challenge), but for me, it seems to work best.

I don't do a lot of AI servo, but when I do, the center point still seems to produce the most consistent results.


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nicksan
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Jul 15, 2009 09:28 |  #3

MarkV wrote in post #8284097 (external link)
I'm no expert on matters of proper AF technique, but I have found that using multiple focus points has yielded inconsistent results in my photography. I use the center point only, focus on my subject and recompose if the subject isn't in the center of the frame. It is definitely a slower method of photography, and may not suit all styles (animals, kids, or anything else that moves "randomly" could be a challenge), but for me, it seems to work best.

I don't do a lot of AI servo, but when I do, the center point still seems to produce the most consistent results.

I don't think he meant using multiple AF points. The center AF point is indeed the most accurate. However a lot of folks, including myself use non center AF points often. I use the AF point closest to the subject and that usually means I am often times not using the center AF point.

Makes sense that the center AF point is best for servo since it is the best performer and it does have the 6 assist points surrounding it.




  
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CyberDyneSystems
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Jul 15, 2009 09:51 |  #4

Especially when shooting "portrait< you really want/need to use an off center AF point.
Don't be scared to use them, that's what they are there for.


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TexRex
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Jul 15, 2009 10:03 |  #5

CyberDyneSystems wrote in post #8284244 (external link)
Especially when shooting "portrait< you really want/need to use an off center AF point.
Don't be scared to use them, that's what they are there for.

Okay. I just thought that the off center focus points would not be as sharp b/c the say f/5.6 this and that. Off center focus points will be more effective than focusing with the f/2.8 center and recomposing? Thx again for the input guys!


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MarkV
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Jul 15, 2009 10:19 |  #6

CyberDyneSystems wrote in post #8284244 (external link)
Especially when shooting "portrait< you really want/need to use an off center AF point.

Why?


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Trey ­ T
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Jul 15, 2009 10:24 |  #7

depend on the limits of DoF, recomposing is never an accurate focus metering, bc you're at different distance. sure it will work fine but you gotta be familiar w/ your DoF limits or range.

those focus points are all metering points, and I do not see why it has to be different than the center metering point. all it does is meter the distance and pull the focus for you. if your subject, where the metering point is at, is not in-focus, then you need to do some microadjustment... but that's another story.


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MarkV
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Jul 15, 2009 10:39 |  #8

Trey T wrote in post #8284438 (external link)
depend on the limits of DoF, recomposing is never an accurate focus metering, bc you're at different distance.

I don't understand that at all. For example, I may want a particular feature of a frame to be in perfect focus, but I may not want that feature to be in the center of the frame. I can set the camera to use automatically selected AF points and hope that the feature is closest to the camera so the focus point covering it will be selected and used, I can manually select the AF point covering the feature, or I can use the center AF point to focus on the feature and recompose. If the center AF point is the most accurate, and recomposing isn't a problem, why would recomposing not be the most accurate method of focusing?


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Trey ­ T
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Jul 15, 2009 11:02 |  #9

here's an example to prove my point:

take out a piece of paper,

-draw a horizontal line to represent a group of ppl standing facing you
-take a pen and set one end as where the camera sit and the other end is the AF point.

if you keep the one end of the pen(camera) and if you point that other edge of pen (AF) to the edge(left or right) of the horizontal line, and then pivot the pen across the line... is it the same distance?


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CyberDyneSystems
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Jul 15, 2009 11:07 |  #10

MarkV wrote in post #8284401 (external link)
Why?

I like to focus on the eyes as opposed to the belly button :)


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CyberDyneSystems
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Jul 15, 2009 11:16 |  #11

MarkV wrote in post #8284518 (external link)
... or I can use the center AF point to focus on the feature and recompose. If the center AF point is the most accurate, and recomposing isn't a problem, why would recomposing not be the most accurate method of focusing?

Because "Focus using center and Recompose" certainly can be a problem.
There is large volumes of information to support this.
LINKS (external link)
If your stopped enough to allow for a reasonable margin for error, focus recompose can work perfectly, or you may be super skilled and or lucky enough to have your cameras imaging sensor remain at exactly the same distance from your subject after your re-compose,.

...but IMHO the odds are far better in your favor to select the AF point that is over the area you want in subject and NOT recompose.


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jacobsen1
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Jul 15, 2009 11:31 as a reply to  @ CyberDyneSystems's post |  #12

^ in theory, sure it's an issue, but in practice I haven't had issues with it. And I've been doing it with a 24L between 1.4 and 2.0.... I also do it with longer fast glass, but the amount you move the 24L changes the images MUCH more. Granted it's DOF is deeper, but yeah, in practice I haven't had huge issues with it.

Of course, in practice, I find the 5Dii to not have the same AF as a 5D and I also find it's outer points to work in lowish light, and hell, better than a 40D in lowish light. So YMMV, $.02 etc. :lol:


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nicksan
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Jul 15, 2009 11:33 |  #13

^Agreed.
You definitely need to watch your DOF, but sometimes I can't get the outer points to latch on and when I don't have the time or patience to get it to work, I'll just switch to the center AF point and try my best not to move the camera too much.




  
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CyberDyneSystems
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Jul 15, 2009 11:46 |  #14

Likewise, in practice, I find the outer AF points to work just fine...
this extra bit of sensitivity offered on the center AF point does not exclude the outer points from functioning very well.

I also use focus recompose often. However, it,.. like the other AF points, is a tool, and each tool has it's place.
If I'm shooting an event in portrait mode for 90% of the shots, I can tell you I am not going to recompose 90% of the time when I can move the AF point once and be done with it.

If I'm working fast, and I'm already on center point, I'll focus recompose, if time allows me to take more shots, then I'll also reselect an ff center AF point and shoot again.
It's mostly about time, and which is more efficient for what your doing.


Anyways I guess my "points" in this thread are these;
- Don't be afraid to use the tools that you have.
- The "spec" on he center AF point should not be considered a reason to use it exclusively.
- Work with all options and develop the style and system that works best for you.
- Just because some can get by with one method, does not mean you should limit your self.


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dr_morbius
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Jul 15, 2009 12:21 as a reply to  @ CyberDyneSystems's post |  #15

I sometimes use the outer focus points, then re-compose. :cool:


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Canon 5DMKII: AF Questions, Thanks
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