Autofocus is the ability of a camera/lens system to automatically adjust the focus of the lens via a motor attached to the focus group of the lens. Contrast with manual focus.
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What is the best way to micro-adjust a lens?
I have a Canon 7D with a 50mm f/1.4 lens, and I think the auto-focus of the lens is off. How can I test and adjust this reliably?
Will this approach work with all of my lenses? If I had a different ...
11
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4answers
6k views
How do camera body motors compare to in-lens motors for focusing?
What is the difference between using a motor on the camera body and the motor built into lenses?
Aside from how both compare in terms of speed, what differences would I notice if I use a body with a ...
24
votes
3answers
644 views
What is the difference between a linear and a circular polarizer?
When I bought my polarizer, a friend told me that I should get a circular one, because the linear ones can mess with the autofocus. Is this true? What should each be used for?
25
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8answers
2k views
What is the advantage to back-button autofocus?
I've heard some advanced photographers talk about using back-button autofocus. As I understand it, this involves changing one of the camera's custom setting to engage the AF when a button on the rear ...
4
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3answers
10k views
Is the lack of AF Motor on the Nikon D5100 an important factor?
I had made up mind on purchasing a Nikon D5100 during the holidays but only yesterday I realized that it doesn't have a AF motor with it.
This is forcing me to change to Canon 550D which is in the ...
31
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3answers
6k views
What apertures are required to enable autofocus, including cross-type or high-precision focusing, on Canon DSLR cameras?
This is a follow-up to Why does Canon and Nikon limit or disable autofocus beyond certain f-numbers? I'm doing this to separate the AF aperture requirements from the linked question above. My goal ...
10
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3answers
606 views
What type of lens will auto-focus on Nikon bodies without a focus motor?
I know my D40 doesn't have a motor in it to auto-focus lenses.
What type of lens has the motor in it? How can I know which lenses will and will not work?
26
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3answers
2k views
20
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3answers
56k views
What does STM mean on a Canon lens?
The upcoming Canon 40mm f/2.8 has a designation of STM on the lens. What does this mean? What are the advantages of having it and does it replace an older technology?
We have a terminology thread ...
24
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4answers
23k views
What is back-focusing?
What is back-focusing? Is it something I need to be worried about, or can I just live with it? How can I tell if my camera/lens is sufferring from it?
10
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2answers
3k views
Why does Canon and Nikon limit or disable autofocus beyond certain f-numbers?
One thing that I've noticed with Canon DSLR camera is they will disable or limit autofocus when the lens is below certain aperture values, which are specified in my answer to What are the aperture ...
12
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4answers
653 views
Why doesn't auto-focus work with an all-white subject (like a wall)?
I am trying to compose a shot using my Nikon D60 and 18-55mm lens towards a white wall in a auto-focus mode.
It looks like I am not able to take the photo. I feel the camera is not able to find any ...
19
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6answers
6k views
What is the practical difference between phase-detect and contrast-based autofocus?
What are the main differences in field use between phase detect AF and contrast based AF?
I understand the technical differences, but I am not sure what the implications from a photographer ...
15
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4answers
1k views
Why can't my SLR autofocus on certain parts of a scene?
I had my Nikon D7000 on single-point auto focus and it just would not focus on the spots I wanted. I have marked the spots that could not be focused on with red circles, and the parts that could be ...
2
votes
2answers
521 views
Do the issues with sharpness I am seeing require AF fine-tuning?
I own a nikon D7000 with 18-105 lens. I am not happy with sharpness I get with autofocus in portraits. I read about front/back focusing, but I am not sure whether my gear has this issue. Is this issue ...
18
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9answers
3k views
Why would I want to select an autofocus point?
I'm trying to understand why I would ever want to select an auto focus point other then the center point. I have a Canon XTI Rebel DSLR which has 9 auto-focus points, but I'm also looking into getting ...
12
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4answers
1k views
How do you use the different autofocus points on your DSLR?
My Nikon D300 has quite a few autofocus points. There's a button I can operate with my thumb to change the autofocus point but I find that quite difficult to use. So I almost exclusively use the ...
10
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1answer
2k views
How does focus work on mobile phone cameras?
How does focusing work on mobile phone cameras?
Aren't their optics simple enough to not have any moving parts whatsoever?
If so, how come most smartphones have an auto-focus, and with various ...
9
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3answers
672 views
Is the color of the AF assist light important?
What are the differences between white and this darkroom red/orange active autofocus assistance lights?
9
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8answers
2k views
Should auto-focus need adjusting?
I own a Canon XTI, and it always seems my shots are slightly out of focus. I usual have my camera set to the center focus point, and usually half press the shutter button to establish the focus on the ...
18
votes
2answers
1k views
Why am I allowed to turn my focusing ring beyond infinity?
Is there a good reason why I can turn the focusing ring on my lenses beyond infinity mark on focusing scale? Following recent questions here and here, it sounds like a real usability issue.
...
4
votes
4answers
454 views
What can I do if autofocus does not work but manual focus does?
Recently, the autofocus on my Nikon D3100 stopped working. The ring of the lens wouldn't even turn when I tried to focus. However, when switched to manual focus, the camera works fine.
When I used a ...
4
votes
1answer
368 views
What is an auto-focus motor?
I recently bought a Canon 550D, and I read it has an auto-focus motor, which not all cameras possess. I'd like to know what it is, and what I can do to keep it running smoothly; AFAIK the manual ...
4
votes
2answers
1k views
What causes auto-focus “freezing”?
On occasion, the auto-focus system in my camera and/or lens just stops working. I'll be holding down the shutter release halfway and tracking a subject and I can feel/hear the auto-focus system ...
13
votes
2answers
2k views
When to use a particular auto-focus mode
I have a Nikon D90, and after taking a photography course that recommended single point auto-focus I predominately use that. I was testing some of the modes today (single point, dynamic area, ...
5
votes
1answer
10k views
What is the difference between Al Focus and Al Servo autofocus modes?
Recently I bought a Canon 60D and I am uncertain about when and how to use/activate the Al Focus and Al Servo functions.
I understand the One Shot autofocus function for still subjects. You press ...
10
votes
6answers
4k views
How can I get everything in focus?
I have a Canon 550D with 70-200 f4 and 50mm prime lenses. Although the camera has built-in 9 focal points, I sometimes face a strange problem. Here's a sample photo:
In reference to the above pic, ...
10
votes
2answers
677 views
How can I determine if my Sigma 10-20mm lens copy is appropriately sharp and focusing right?
I just purchased a Sigma 10-20mm lens (Canon mount) and based on the reviews I was aware that many people receive copies of the lens that are soft or don't focus properly. I purchased from B&H, so ...
24
votes
6answers
3k views
Can I damage the focus system by turning the focus ring when the lens isn't mounted?
I have a couple lenses that don't have an internal focusing system, and whenever I want to put them back in my bag, I turn the focus ring to make the lens shorter.
I noticed that when the lens is set ...
16
votes
5answers
1k views
When would one need manual focus override?
In lens reviews, ability to override auto-focus manually is often referred to as a good (and important) feature.
I have rarely, if ever used that feature, so I feel I might be missing out on an ...
13
votes
2answers
23k views
What's the difference between cross-type autofocus points and regular ones?
What's the difference between different autofocus point types (cross vs point and such)? Cross points seem to be a "feature" — why?
7
votes
5answers
392 views
Precise focus in self-portraiture
I've been trying to take some self-portraits, but I often have to struggle with the auto/manual focus. I don't miss by a lot, but I really want sharp focus in the eyes. I'm using a 50mm/1.8 around ...
6
votes
4answers
575 views
Which is better - autofocus and recompose vs. manual focus?
In some occasions autofocus doesn't focus what I intend it to. What is the better option - to use autofocus, focus what I want and recompose, or use manual focus in that situation?
5
votes
6answers
8k views
Why does my Nikon D3100 no longer auto-focus correctly?
I bought my camera on January 2011. Since a few months ago, I'm facing a problem with the autofocus.
It happens with my two lenses 18/55mm and 55/200mm. I noticed that the focus light doesn't turn on ...
5
votes
2answers
659 views
Can't auto-focus at full zoom
I have a Canon 1000d, and the standard lens EF-S 18-55mm. Recently I was out taking photos and I've noticed that if I zoom in fully, the lens can't auto focus. I can still take shots using manual ...
3
votes
2answers
779 views
Is it really better to not half-press to focus with the Fujifilm X-Pro 1?
Fujifilm's new camera uses contrast-detect autofocus, and the current Internet hand-wringing is over whether this is a horrible critical flaw or not. As often happens in such discussion, a bit of ...
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2answers
767 views
Automatic autofocus on 600D/Rebel T3i during video mode [closed]
I was testing the video mode with my 600D, and I noticed autofocus was not working. I then enabled it via the menu and now you can focus when pressing the main button. I was wondering whether this is ...
10
votes
1answer
180 views
When focusing in Live View, where is the point of focus?
I use Canon SLRs. When using live view focusing, there is a rectangle which turns green when the focus is achieved.
My question is: Is there a single focus point at the center of the rectangle? Or ...
8
votes
3answers
154 views
Is there a rating, spec or measurement that a buyer can use to compare how fast cameras can autofocus?
I know that Phase Detection autofocus is faster than Contrast Measurement autofocus.
Is there a spec that can tell me whether one DSLR or compact camera can achieve autofocus on a subject faster ...
8
votes
2answers
760 views
Can lens focus speed affect continuous shooting speed?
I was using a 50mm f/1.8 II lens on my Canon 40D yesterday, and I was trying to capture some action shots using continuous high-speed drive mode and AI Servo autofocus mode. I was using a shutter ...
7
votes
1answer
4k views
Can I fine tune the autofocus on my Canon 60D to be more accurate?
I noticed that some of my lenses auto-focus more accurately then others. (Assume perfect light conditions and fast shutter speed) Zooming-in on say the center focus point (if only the center focus ...
7
votes
2answers
429 views
What is being set with Micro Focus Adjustment?
An autofocus system is system based on a feedback loop, where the AF sensor error reading if fed back to the lens focus motor. Being a closed loop, then theoretically there should be no focusing ...
7
votes
2answers
503 views
Why the AF confirm lights won't blink when the spot is in-focus while using an all-manual lens with an adapter without any connectors?
I understand that my Canon 450D's (XSi/Kiss X2) passive autofocus system knows a spot in the view is in-focus when its nearby contrast is adequate. Then the camera blinks AF confirm lights to inform ...
7
votes
2answers
718 views
How do I focus a Nikon 50mm f/1.8?
I recently bought this lens, but it seems to me that it hunts a lot in low(ish) light, and sometimes (often) does not achieve focus at all. I never had any problems with the kit lens.
Pointing the AF ...
6
votes
6answers
1k views
Is it important that the Canon 1DX isn't specified to autofocus with lenses slower than f/5.6? [closed]
Seeking the lens market AND the related info WRT Canon 1D X, I found some things which seems concerning:
1st, a note from Canon's Chuck Westerfall (see here) saying:
“AF is unavailable on the ...
5
votes
1answer
385 views
Why isn't the focus indicator light showing when focused on my Canon 5D Mark III?
I've been working with two different Canon EOS 5D mark III cameras, and had the same problem with both.
When auto-focusing I have two kind of indicators when the image is focused on a certain point.
...
5
votes
1answer
199 views
Where is the AF sensor located in a DSLR?
As I understand every DSLR has a separate, smaller sensor that handles phase detection focusing. Where is it located?
If this location is different for every DSLR, and therefore this broad question ...
5
votes
4answers
363 views
Replacing my XXD with a 7D?
My goto camera is still my 5D Mark II. As I primarily shoot landscape, I love Wide Angle on a Full Frame body.
That said, I do occasionally shoot animals and people running.
The 5D Mark II's AF ...
5
votes
1answer
790 views
Sigma 70-200mm vs. Nikon 80-200mm auto-focus speed
I'm considering the newest Sigma 70-200mm F2.8 EX DG APO MACRO HSM II and comparing it against the older (but still for sale) Nikon AF 80-200mm F2.8 D ED.
These are roughly in the same price class, ...
4
votes
2answers
3k views
Could autofocus of the Canon t4i be improved with a firmware update?
I am trying to decide between the Canon t4i (650D) and the t3i (600D). Initially I was going for the t4i because of the autofocus. But the sample videos I have seen did not really impress me.
Can I ...
