Spring 2012

Spring 2012
by ani

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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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51
votes
5answers
19k views

What is the best way to micro-adjust 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 ...
30
votes
3answers
2k 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?
18
votes
4answers
13k 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 ...
43
votes
4answers
24k 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 ...
28
votes
8answers
4k 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 ...
37
votes
3answers
295k 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 ...
15
votes
4answers
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 ...
25
votes
9answers
4k 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 ...
11
votes
6answers
11k 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
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?
7
votes
2answers
5k 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 ...
21
votes
6answers
29k 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 ...
31
votes
3answers
6k views

How does autofocus work?

How does auto focus work on modern cameras? How accurate is it?
7
votes
1answer
2k 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 ...
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 ...
35
votes
4answers
63k 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?
25
votes
3answers
10k 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 ...
33
votes
5answers
4k 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. (...
16
votes
2answers
9k 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 ...
21
votes
3answers
2k 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. ...
6
votes
1answer
1k 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 ...
1
vote
4answers
1k 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?
1
vote
1answer
347 views

Pictures start in focus then go out of focus?

I was recently shooting some surf 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 the ...
12
votes
3answers
6k 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, ...
3
votes
2answers
7k 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 ...
16
votes
2answers
28k 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 ...
27
votes
6answers
7k 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 ...
13
votes
4answers
1k 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 ...
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 ...
5
votes
2answers
7k 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 ...
4
votes
2answers
762 views

Does having the AF points bunched up in the middle make a big difference?

I was looking into the new Nikon D600, which looks like a pretty compelling camera. I however noticed that its 39 AF points though quite a lot are all bunched up in the middle. I am used to having AF ...
4
votes
1answer
896 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 doesn'...
3
votes
4answers
58k views

What should I do when my Nikon AF-S lens won't auto focus?

I have a Nikon 35mm f/1.8G AF-S DX I bought for my Nikon D5100, it's only a couple months old, never been dropped or anything, and it all of a sudden won't auto focus. Anyone know if this is a simple ...
1
vote
3answers
12k views

What does the AE 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 ...
0
votes
3answers
814 views

Why are my photos taken with the Sigma 18-50mm f/2.8 coming out blurred?

I'm new to photography, and I don't know why the pictures I'm taking are coming out blurred. Here's a sample image, taken with the Sigma 18-50mm f/2.8 on my Nikon D5200 at 18mm, 1/60s, f/2.8 and ISO ...
16
votes
2answers
5k 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-...
24
votes
2answers
73k 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?
9
votes
3answers
788 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?
9
votes
3answers
2k 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
votes
8answers
4k 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 ...
2
votes
3answers
12k 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 ...
6
votes
4answers
3k 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 ...
6
votes
6answers
2k 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 EOS-...
5
votes
2answers
139 views

Does “the same” lens, with different autofocus systems, have the same optical quality?

I'll give examples with Nikon only, but the question is pretty general. So, is this a fact or not? Examples: Nikkor 50/1.8G AF-S, Nikkor 50/1.8 AF-D and Nikkor 50/1.8 AF 70-300 AF and 70-300 AF-S ...
5
votes
1answer
39k views

Which Nikon DSLRs have an autofocus motor in camera body? [closed]

I have a Nikon D3000 and a lens which has no autofocus motor. But under the lens, I have found a screw which rotates with the focusing control. My D3000 does not have any autofocus motor inside the ...
5
votes
2answers
590 views

Are of 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.
5
votes
8answers
16k views

How can I focus in very low light with my Canon 60D?

I'm using a Canon 60D and would like to focus in low light. I know Canons — in fact, all cameras — can struggle here with auto focus, but I'm talking about light so low that I wouldn't be able to see ...
4
votes
1answer
412 views

What autofocus zone selection mode should I use for action/event shooting?

I have a Canon 7D, and typically shoot everything I do in its single-point autofocus zone select mode, because I usually want fine control over exactly what the camera is focusing on and I often find ...
3
votes
2answers
2k 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 ...
3
votes
4answers
1k views

Will any non-AF lens work on a Nikon camera with built in AF already in the camera body?

I want to purchase a camera with a built in autofocus motor, but I want to know if lenses without autofocus will then focus automatically on that camera body. In other words, can I buy a Nikon camera ...