Questions tagged [autofocus]

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.

Filter by
Sorted by
Tagged with
7
votes
2answers
5k views

How do I diagnose the source of focus problem in a camera?

Probably a novice question, but how do I correctly diagnose from a photo for what reason that camera wasn't able to focus properly? It can be any 1 of the following Unsteady hand Lens issue Metering ...
54
votes
5answers
23k views

What methods can be used to micro-adjust autofocus of a camera body to a particular 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 ...
3
votes
1answer
971 views

Pictures of surfers start in focus then go out of focus?

I was recently shooting some surfers after a session with my 7D and Tamron 18-270mm F/3.5-6.3 Di II VC PZD. I started shooting while he was in focus, then as he got to the main part of the maneuver ...
38
votes
5answers
6k 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?
7
votes
1answer
3k views

Which offers better results: FoCal or LensAlign Pro?

I am in need of microadjusting my autofocus for a couple of my lenses with my Canon 7D. Namely, I need to adjust the 100-400 L lens, which seems to consistently AF a bit softer than I've seen from ...
48
votes
3answers
391k views

What does STM mean on a Canon lens?

The Canon EF 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 that ...
8
votes
2answers
6k views

If the focal plane is curved, should the outer AF points work correctly or front-focus?

Many (all?) lenses have a (slightly) curved focal plane. In general it's close enough to flat that you don't really notice it, but under certain conditions it may become apparent. As I understand it ...
22
votes
4answers
17k 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 ...
2
votes
4answers
2k views

Will the Canon 5D MK II with 100-400 1:4.5-5.6 work properly with Kenko 1.4 converter?

I'm using 5D MKII body and 100-400 f/4.5-5.6 lens. I want to use a 1.4 converter; will the Kenko converter work and autofocus properly?
12
votes
7answers
18k views

How can I get everything in focus? (Why can't my camera just use all of its focus points at the same time?)

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, ...
33
votes
8answers
5k 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 ...
18
votes
1answer
6k views

Why do some lenses focus past infinity? [duplicate]

On the kit 18-55 lens that came with my Nikon D5100 I have noticed that when trying to focus on infinity for shots in dark conditions (star-trails, etc) the lens tends to move past infinity out of ...
12
votes
3answers
2k 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?
35
votes
3answers
13k views

How does autofocus work?

How does auto focus work on modern cameras? How accurate is it?
3
votes
3answers
2k views

How can lens cause consistent front or back focus?

I can understand body focusing problems, but I can't imagine why lens might cause front or back focus. I have two third party manufacturer lenses for my Nikon: one is front-focusing, the other is back-...
48
votes
4answers
36k 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 ...
31
votes
9answers
5k 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 ...
18
votes
5answers
2k 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 ...
3
votes
2answers
8k 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 ...
7
votes
3answers
21k views

What does the AE/AF lock button do that half-pressing the shutter doesn't?

The Sony A6000 has an AEL button, while Nikon SLRs have an AE/AF lock button. What do these do that half-pressing the shutter to lock focus and exposure, and then recomposing, doesn't? I'm used to the ...
24
votes
3answers
3k 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 about focusing in the dark (here and here), it sounds like a ...
7
votes
3answers
3k views

Does autofocus work better with f/2.8 lenses vs f/4 or slower?

I read following in a web site (http://realphototips.wordpress.com/tag/ai-servo/) Lenses with maximum apertures of f2.8 allow the camera to use all high precision sensors. In low light or other ...
38
votes
5answers
6k views

Focus problem vs. motion blur vs. camera shake - how to tell the difference?

I'm not sure if the title of the question captures what I mean, but it's hard to be succint in the space allowed. Suppose you have a picture that is not as sharp as you think it should/could be. (...
22
votes
6answers
40k 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 ...
3
votes
5answers
19k views

Why my “action” shots are blurry even shooting on AF-C, is this a lens or camera limitation?

I'm currently using a Nikon 28-200mm AF-D with my D7000. While trying to take action shots (e.g. my dog running or sports) none of the shots seem to be in focus even on AF-C mode. Would this be a ...
37
votes
4answers
93k 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?
46
votes
7answers
9k views

How did photography work before auto-focus was invented?

Having just spent some time reading questions about auto-focus, I came up with a question of my own: How did cameras even work before auto-focus technology was invented? Presumably everybody used ...
15
votes
8answers
2k views

What features would cause a portrait photographer to choose a DSLR over Mirrorless?

With the new line of mirrorless cameras being announced this fall, the gap between DSLR and mirrorless cameras continue to close. There are many generic discussions comparing the two, but as a ...
30
votes
3answers
186k views

Why do higher end lenses use USM instead of STM?

Canon has a newer type of motor, called STM, which is introduced in lenses like 18-135 f/3.5-5.6 IS STM, 40 f/2.8 STM and so on. STM also provides quick, silent and smooth focusing. Even the focusing ...
9
votes
2answers
3k views

Are cross-type focus points more accurate, or just faster?

Do cross type focus points achieve sharper photos than horizontal points or do they just grab focus faster?
6
votes
4answers
18k 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 ...
13
votes
3answers
12k views

What is Nano USM and how does it compare to an STM or USM lens?

The Canon EF-S 18-135mm f/3.5-5.6 IS USM has a designation of Nano USM on the lens. What does this mean? What are the advantages of having it vs STM or USM? We have a terminology thread that usually ...
4
votes
3answers
34k views

What does infinity focus mean and when should I use it?

All my lens have focus ring where at the end there's an infinity symbol. What does that mean? If I'm taking landscape shot and what everything from near to far to be in focus, do I use infinity? Or am ...
30
votes
3answers
34k views

What is the advantage of the huge number of AF points?

If the camera has only 1 central AF point, it is difficult to focus on an off-center subject (without recomposing after autofocus) so having 3 AF points seems really useful. Similarly I understand the ...
15
votes
3answers
7k views

Why do mirrorless cameras have quicker autofocus than SLRs using live view?

With early 2013 cameras, it's generally accepted that using contrast detection autofocus on SLRs (ie live view on most SLRs) is something which is really suitable only for static, or close to static, ...
17
votes
2answers
13k 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' maximum aperture is narrower than certain values, which are specified in my answer to What ...
4
votes
2answers
404 views

How can I more consistently focus on the point I want?

I've had so many wonderfully composed images turn out lousy because my AF isn't as accurate as I'd like (or I don't know how to wield it). Despite using single-point AF, my focus point is often ...
1
vote
1answer
3k views

Autofocus points in Mirrorless Cameras

Some mirrorless camera such as Sony Alpha 6300 has a lot of AF points (425), whereas flagship DSLR like Canon 1DX Mark II "only" has 61 AF points. Nikon D5 has 153 but it is still way lower than this ...
6
votes
2answers
5k views

Why is on sensor PDAF drastically slower than traditional PDAF?

Why is on sensor PDAF drastically slower than traditional PDAF? I assume the technology is the same, doesn't matter if the module is on the sensor or located behind a mirror. But the performance is ...
2
votes
1answer
24k views

Why isn't my Canon 70D autofocus accurate in manual zone AF mode with a 50mm f/1.8 lens?

I recently purchased a Canon 70D for its dual pixel autofocusing system and ISO performance. I am in love with this feature rich-camera; however I found the camera's autofocus fails to function ...
13
votes
4answers
2k 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 ...
10
votes
3answers
1k views

What motor gets used if both lens and camera body have a focus motor?

If both a camera body and lens have motorized autofocus, would one be used over the other or would both work in tandem to speed the focus process along?
7
votes
1answer
2k views

Why are photos taken with my old lenses all out of focus on my new Nikon D5300 body?

My Nikon D80 died, and I was bought a new D5300, body only. All the photographs are out of focus when I use the lenses I used with my D80. Why would this be? I'm using the Sigma 18-50 f/3.5-5.6 DC, ...
3
votes
2answers
5k views

Do separate autofocus motors exist for entry level Nikon DSLRs?

I have a Nikon D3200, which doesn't have an autofocus motor. Therefore, I'm mostly deterred by lenses that don't have focus motors in them. But the ones that do have it are much more expensive. Take ...
21
votes
2answers
41k 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 ...
29
votes
6answers
12k 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 ...
12
votes
4answers
2k 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 ...
9
votes
3answers
14k views

How to enable Canon AF with teleconverter?

Canon DSLR bodies prevent poor auto-focus performance by disabling it completely when the lens reports maximum aperture at chosen focal length smaller than f/5.6. This implies that some lenses will ...
5
votes
2answers
9k views

What is the effect of the number of cross-type focus points on sharp focus?

Canon claims that EOS 6D has special capability to focus in low light, but it has only one cross-type sensor and overall only 11 focus points. Does only one cross-type focus point in the Canon EOS 6D ...
5
votes
5answers
2k views

Why does the autofocus capability depend on the aperture rather than the amount of light available?

In many DSLR manuals one can read something to the effect of: Maximum Lens Aperture: f/3.2 - f/5.6 With all AF points, cross-type AF sensitive to both vertical and horizontal lines is ...