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Old 09-20-2014, 08:50 PM
 
3,490 posts, read 7,356,685 times
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This is probably something really basic that I am screwing up, but I am having trouble with focussing on a subject (almost always a fast moving toddler) when she is behind something else. Usually flowers, branches, snow flakes or whatever else.

It's frustrating and I have missed some amazing pictures due to my focussing issues. And by 'amazing' I mean pictures where she is smiling
When she is smiling she is often also moving.

Camera is a new Canon Rebel T5i with a EF50 lense.

How can I focus on her rather than whatever happens to be in the foreground? She is always moving so it needs to something I can change quickly as I follow her around.



Examples.

In focus



Out of focus:



In focus



Out of focus (I know this image has other issues but you get the idea



Another:



My latest issue.
In focus:


Out of focus:




Any tips would be most gratefully received! Thank you!

Last edited by Hobokenkitchen; 09-20-2014 at 09:04 PM..
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Old 09-20-2014, 09:19 PM
 
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I guessing "Single Point Selection" may help. This is the easiest description I could find on how to make the change.

How to Switch from Automatic Point Selection to Single-Point Selection on the Rebel t5i

And a more detailed discussion of the autofocus system -

Picturing Change Taking Control of Your Canon Autofocus System
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Old 09-20-2014, 09:51 PM
 
3,490 posts, read 7,356,685 times
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Quote:
Originally Posted by BendLocal View Post
I guessing "Single Point Selection" may help. This is the easiest description I could find on how to make the change.

How to Switch from Automatic Point Selection to Single-Point Selection on the Rebel t5i

And a more detailed discussion of the autofocus system -

Picturing Change Taking Control of Your Canon Autofocus System
Thank you!!!! I am going to have a go at this tomorrow. I'll report back with my progress (or lack thereof, lol).
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Old 09-21-2014, 12:00 PM
 
Location: Not far from Fairbanks, AK
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Use Av mode instead of fully automatic. The next steps are as follows:

a. With plenty of daylight as shown on your photos above, set the ISO around 200 or so, and the lens aperture around f/4 or wider. If having trouble with the ISO speed, just set it to auto ISO

b. Set the camera to AI-Servo, then the to burst mode, and use the center focus point

To check if the shutter speed is correct, press the shutter button half-way as you look at the subject through the viewfinder. The shutter speed should be high enough to stop motion.
-------------

If you are still having trouble and are using the camera on one of the automatic modes, then switch it to the "Sports" mode, which is the one showing a skier figure on the mode wheel. In this mode the camera uses AI-Servo, the correct focus point, and everything else automatically.
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Old 09-21-2014, 04:15 PM
 
Location: Bellingham, WA
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Your camera may have a focusing mode that will track the subject as she's moving. I believe Canon calls it "AI Servo". Another possibility, if you're using Canon's most affordable 50mm 1.8 lens and you're shooting it wide open at f1.8, I always found that, a) that lens is kind of soft wide open, so it can look like it's not perfectly focus, and b) it can be focused on something tiny, and the depth of field can make the rest of the image look slightly out of focus (usually only happened when shooting at very close range, though).
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Old 09-21-2014, 05:23 PM
 
Location: Dallas, TX
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Based on the OOF images above, it appears the issue is not due to movement, but a confused AF system where it found something in the foreground to focus on. A simple fix would be Single point AF instead of "wide". Wide may be useful if the camera is being used to track movement across the frame. On some advanced cameras like Sony a77, Canon 7D etc, you can typically choose "wide" but within a smaller zone somewhere in the frame. But to keep it simple, try single point.

Continuous AF will help only if the subject is moving and especially coming towards you (or moving away).
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Old 09-21-2014, 09:18 PM
 
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Quote:
Originally Posted by EinsteinsGhost View Post
But to keep it simple, try single point.
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Old 09-22-2014, 06:20 AM
 
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Ok this is all very helpful - thank you!
I currently shoot on AV or full Manual Mode. Rarely on fully automatic unless I'm having a lot of trouble with my settings - for example if it's really dark and she's running around.

Would the single focus point help me out with a situation like her hiding behind a huge beach ball with just her face showing above the ball (for example). In this kind of case I wouldn't know exactly where her head is going to pop up. Would I make my best guess and select the single point of focus at the expected spot?

How about the pic in the playhouse with the head overlapping hers?

I couldn't get out to practice yesterday, but I'll see if I can today. I need a place with grasses and flowers or twigs in front of her. I was particularly disappointed about the second wildflower pic because that expression is so her, and I love that she's holding the flower (the thing I focused on - arghhhhh).
The likelihood of me getting that set up again is practically zero.

I will report back. : )
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Old 09-22-2014, 06:25 AM
 
Location: SC
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Change the f-stop (depth of field) to something wider.

Instead of focusing on a subject 15 feet away, set the camera to focus on something between 12 and 18 feet away - with your subject 15 feet away.
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Old 09-22-2014, 11:48 AM
 
Location: Dallas, TX
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Quote:
Originally Posted by Hobokenkitchen View Post
Ok this is all very helpful - thank you!
I currently shoot on AV or full Manual Mode. Rarely on fully automatic unless I'm having a lot of trouble with my settings - for example if it's really dark and she's running around.
Low light introduces additional variables such as low contrast (camera's AF system needs good contrast to respond faster and more accurately), slower lenses can also require higher ISO (loss of detail, and/or motion blur due to shutter speed not being fast enough... if any movement is involved). It can also be due to shallower Depth of Field (you may choose larger aperture to take in more light and get faster shutter and/or lower ISO).

Quote:
Would the single focus point help me out with a situation like her hiding behind a huge beach ball with just her face showing above the ball (for example). In this kind of case I wouldn't know exactly where her head is going to pop up. Would I make my best guess and select the single point of focus at the expected spot?

How about the pic in the playhouse with the head overlapping hers?
Single Point AF should help. Of course, there is still a chance for the camera's AF to be confused (it would really depend on quality of the AF system). Here is an example taken through a fence that you can see as blue on opposite ends of the frame, which could have easily confused the camera (at the very minimum, there was a potential for "hunting" as the camera tries to find what to focus on):

Sony a55 w/16-50/2.8 SSM

Something also worth considering (for greater accuracy) would be use of cross-type sensor(s) more. I am not familiar with your camera, but I'd assume it to have at least one cross type and most certainly in the center. The difference between a cross type and a line sensor is that the former uses two cross lines and looks for "phase change/contrast" in two places as opposed to one which would be true for a line sensor. Some advanced cameras have a high number of cross-type sensors, as is the case with this Sony a77 II which uses 79-point AF system, 15 of those (shown in green and in pink below) are cross-type:


Here is another example and in this case, the challenge is a bit different, as I was using a camera that uses "Contrast Detect AF system" which, while can be more accurate than Phase Detect AF used in DSLRs, can also get confused rather easily.


Using "wide" AF would have been a pain. Center AF would have worked, but I had a twig running across the middle. I used "Local Spot" AF, choosing a AF point on the bird and away from the branch.
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