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
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 ...
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 ...
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 ...
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 ...
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. (...
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?
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?
36
votes
5answers
5k views

Why are some big telephoto lenses so expensive compared to telescopes?

I'm looking at an ad for a used Canon 1200mm f/5.6L EF USM Autofocus Lens where they are asking $180,000. Yes, that's not a typo. I don't get it. I'm an amateur astronomer and I know I can buy a ...
35
votes
3answers
13k views

How does autofocus work?

How does auto focus work on modern cameras? How accurate is it?
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 ...
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 ...
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 ...
30
votes
3answers
33k 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 ...
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 ...
25
votes
2answers
83k 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?
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 ...
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 ...
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 ...
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 ...
19
votes
1answer
2k views

Why do even high-end cameras often still include normal (non-cross-type) AF sensors?

Modern cameras often use two kinds of AF sensor: normal, and cross-type. While normal-type AF sensors notably struggle focusing on high-contrast vertical lines, cross-type sensors, though more ...
19
votes
3answers
2k views

Why don't cameras have autofocus points in the edges and corners?

On all the DSLRs I've used, there are never any autofocus points near the edges and corners. Why is that?
19
votes
4answers
4k views

How can I get better focus when a subject is moving towards or away from the camera?

When shooting events or action photos, engaging people, I often find that frontal (or rear) perspective may be very expressive, but my problem is focusing when the subject moves towards the camera (or ...
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 ...
18
votes
4answers
1k views

How to speed up autofocus on moving subjects under low-light conditions?

Since I am usually taking pictures under low light ambient conditions I have discovered the nifty 1.4 lenses (such as the Sigma 30mm/1.4 or the Canon 50mm/1.4 or also the Canon 85mm/1.8) for my Canon ...
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 ...
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 ...
17
votes
6answers
5k 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 ...
17
votes
1answer
15k views

What is a focus limiter?

What is a focus limiter and how does it work? What is the advantage of it? For instance Tamron 90/2.8 Macro has a focus limiter. According to the documentation: In the limit position, the Tamron 90 ...
16
votes
6answers
8k views

Why aren't faces sharp in my f/1.8 portraits even though I'm carefully using center-point autofocus?

I love my Canon Rebel T6 and take portrait pictures in Av mode with a 50mm in 1.8 Av. I'm using auto focus in the 'focus on center point' mode. I make sure that the center point focuses on the face so ...
16
votes
3answers
6k 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, auto-...
16
votes
5answers
2k views

How to improve focus accuracy?

I've noticed that quite a few of my photos aren't terribly well-focused. This particularly happens at long focal lengths. I'm using a Canon 500D and (mostly) a Tamron 18-270mm f/3.5-6.3 lens. I find ...
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 ...
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, ...
15
votes
4answers
1k views

Why aren't lenses designed with extra large apertures for autofocus beyond what's used for imaging?

Historically, designing large-aperture lenses has been difficult because correcting the optical aberrations that arise from large apertures requires complex designs and very large amounts of glass. ...
15
votes
2answers
1k views

Where can I find advice on using an advanced AF system for wildlife and bird photography?

I recently purchased a Canon 7D, as my previous 450D had become a severely limiting factor in my endeavors to wildlife and bird photography (particularly bird photography, which I LOVE, but for which ...
15
votes
3answers
716 views

At which lux level do the Nikon 1 cameras switch from PDAF to contrast-detection?

The Nikon 1 cameras are famous for being able to track focus with their on sensor PDAF. But the story goes that if light is low, it will switch to contrast-detect only and will not track focus as ...
14
votes
4answers
4k views

Do I need to turn off camera before switching auto-focus on/off?

I have a Canon 700d with 2 kit lenses, both having auto-focus feature. I read a book "Canon EOS Rebel T5i/700D For Dummies", which warns against switching auto-focus on/off while the camera is on. ...
14
votes
6answers
5k views

Why don't most cameras use infrared for focusing?

All auto focus assist lights are either red or white. Why do DSLRs not use infrared instead? It seems it would be beneficial to a photographer to not blind their subject before taking a picture. I'...
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 ...
13
votes
6answers
2k views

How can I improve focus using both manual and auto on a candle flame?

I got my new tripod and 50mm F/1.4 sigma on my Nikon D7000 and was testing it out doing some shots of a flame on a candle. The below image is the sharpest i was able to produce. In review of my 50+ ...
13
votes
10answers
17k views

Is there a D-SLR that can record video with continuous autofocus?

Is there a D-SLR (including the new Nikon and Canon 60D) that can take video with continuous autofocus? On cameras that don't support that feature, is it possible to autofocus by pressing a button ...
13
votes
3answers
4k views

How does the lens influence the autofocus?

I think I've more or less understood how AF works now. However, I'm not sure how the lens influences the whole process. In my recent research for my next lens I found reviews stating the one lens' AF ...
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 ...
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 ...
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, ...
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?
12
votes
3answers
28k views

Will the Nikon D3100 autofocus with the 50mm f/1.8D lens?

I have the Nikon D3100 and was wondering if the autofocus on the Nikon 50mm f/1.8D lens would work with it. I've read that the AF is not compatible with the D5000, and that the AF is rather slow in ...
12
votes
3answers
1k views

What is manual-priority autofocus?

I have been looking at the Nikon AF-S 35mm f1.8 lens and it has two focus settings: Manual Focus Manual-Priority Autofocus What is "manual-priority autofocus"?
12
votes
2answers
2k 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 ...
11
votes
1answer
1k 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 ...