Beginner Auto Focusing Issues- Canon 70D

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366
Name
Simon
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#1
Good afternoon,

I wonder if someone could answer/throw some light on something for me?
For some time I have been convinced that I am suffering a focusing issue on Auto focus. I shoot mainly landscapes and my eyes are not what they were so I tend to rely on auto focus on early morning shots. I did an early/dawn road trip to Aldeburgh yesterday for dawn and it didn't let me down. However, I always have to play with the sharpness on my images in PP. So, this afternoon I took a couple of pictures in the garden, Canon 70D, 18-135mm is stm lens, all at 135mm but running through the aperture values. I have always shot on f8 (because that's what the general consensus of opinion says) and was rather shocked at the results. The first image is at f8 and the second at f11, looking at the background in the first image, it appears to be focusing on the gravel board, not the dog. I am I right in thinking the second image at f11 is sharper because of the greater depth of field f11 gives? Is this something I can adjust?

016a.jpg 018a.jpg

Many Thanks in advance.
Simon
 
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11,794
Name
Rich
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#2
Hard to say because you might have focused on the dog in the 2nd photo.
Very limiting just sticking to f/8, use whatever is appropriate to your subject and available light
For instance this dog where you might wish to blur the background by using a larger aperture number such as f/2.8
Try a few shots with small single centre focus point and see if it consistently back focuses, wouldn't start messing with micro adjust yet
That is often the road to madness, two clicks one way and three back the other, but yes it can be adjusted if required
See here for more information https://www.slrlounge.com/canons-free-autofocus-microadjustment-guidebook/
 
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8,455
Name
wayne clarke
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#3
Hard to say Simon as theres a lot of variables. What focus point are you using, single point or several ponts.
Find something with lots of nice detail, use single point and see what it does. Another test is to switch to manual focus, use live view and magnify the image on the screen and focus manually on the test subject, at least that will tell you if the lens is not a duff one.
What area are you based? Maybe someone local could meet up and try a different lens to see whats going on.
 
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546
Name
Clint
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#5
I think you have to separate technique from technical. It would help if you describe in detail how you use your auto focus. Canon have three types of AF. Single shot, AI and Servo. Most of my out of focus shots are from AI and servo. When you select your AF points do choose single point or all or clusters (groups) ?
 
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sparker
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366
Name
Simon
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#6
The above images were taken with the camera on a tripod, single shot, single point Auto Focus (back button focus), the the same focus point was used in both images. I took the first, changed the aperture value, re-focused using the back button focus and took the second. Nothing else was altered.
 
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3,476
Name
Dominic
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#7
I think a better test would be to stand 5 AA batteries, in a line, on a table, so that there is a finger width gap between them. Auto focus on the middle one, with a wide aperture. Take a shot and see if it has focused correctly. I would also do the same in live view, as it is a different focus system (focuses using the sensor)and will help you decide if it's a lens issue (not likely though) or a Auto focus issue.
I hope that makes sense.
 
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546
Name
Clint
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#8
I would try using single point but without the back button. I think the back button is linked to servo. Try a different AF point in case there is dirt on the AF sensor in the camera.
 
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1,278
Name
Tim
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#9
Where was the focus point on the dog? Depending on how far away you were you may only have a few cm of DOF. For example if the dog was 1.5m from the camera then your DOF at 135 / f8 is only 3cm, so much of the dog will be out of focus regardless. At f11 DOF increases to 4cm at that distance. Second thought is that the single focus point needs some contrast to work afaik. I’d suggest trying it again and picking a focus point with contrast, the eyebrow and checking that part is in focus. If that doesn’t work then line up the batteries as above and check AF micro adjustments.
 
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23,442
Name
Phil
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#11
I would try using single point but without the back button. I think the back button is linked to servo.
It isn’t unless you have done something weird, the back button should perform the same function as the half shutter press, in either single shot or servo.
 
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546
Name
Clint
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#12
It isn’t unless you have done something weird, the back button should perform the same function as the half shutter press, in either single shot or servo.
You’re probably correct. Most people use it linked to servo so I just thought it was always.
 
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13,208
Name
Toni
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#14
The first image is at f8 and the second at f11, looking at the background in the first image, it appears to be focusing on the gravel board, not the dog. I am I right in thinking the second image at f11 is sharper because of the greater depth of field f11 gives? Is this something I can adjust?
It looks to me like the first image is focussed well behind the dog, while the second may be slightly in front. I'm sure it's not the difference between f8 and f11 DoF.
 
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