I got a Canon 70D a couple weeks ago from Amazon. As explained here and many other places around the internet, its autofocus system doesn't work as one might think it does. The focus "point" actually covers a large area.

This has led me to many out of focus shots, even when anticipating its modus operandi. It's simply not reliable, no matter how you look at it: When taking a picture of a person looking at you from a top view, ~6m away @55mm, 1/160, 5.6f you'll be lucky to get the face focused. Often times the camera will focus on the grass ground, if it's better lit/contrasted than the face. (The important thing about those settings is that since the face is 6m. away from you it will not cover the majority of any AF cross even if it's dead-center on)

This is very easily tested just staying still and trying to autofocus on the very same spot repeatedly: you'll feel the lens focusing each and every time in a slightly different spot, every time.

I love the camera otherwise, the video is simply awesome and the pictures that come out sharp look simply great. So, I'm seriously considering returning it. I need consistent autofocus. I need to know that when I select an AF point covering a face, the face will get the focus and nothing else will.

I am thinking that a camera with more autofocus points — say, 51 instead of my camera's 19 — will allow more precise selection of the target I really want. But I don't want to spend thousands of dollars to find this out. If you've used both AF systems with a few points and the newer, more expensive ones with many points, can you confirm this? Will more autofocus points make it easier to focus on small targets even when the background is high-contrast?

  • Thank you, I understand, and you can see I already stated that on the question, but that phrasing wouldn't actually reflect what I'm trying to ask. I know how to get somehow consistent focus on a face with a mid-tier DSLR in certain conditions but as soon as that face doesn't fully cover an AF cross the results are unpredictable and most of all, inconsistent from shot to shot. This is by design, which is why I'm asking if Nikon's design is any better.
    – MrMerrick
    Jun 29 '15 at 20:18
  • I don't get the downvotes and close requests from others. However, MrMerrick, you should clean your question up so that it is more to the point and easier to read. Or ask your question in two parts.
    – TFuto
    Jun 30 '15 at 12:09
  • @TFuto yes, I should have been more to the point and maybe more technical. English is actually not my first language. However, given the downvotes and being the most voted answer one that "accuses" me of just wanting to buy another camera (wtf?) or simply not knowing how to use it... I think I'll let it slide this time and look elsewhere for help. Thanks!
    – MrMerrick
    Jul 1 '15 at 7:43

You linked to that other question, stating that AF systems do not work as one thinks. Oddly, you come to the conclusion that you should buy another camera.

Let me quote from the accepted answer:

The Canon 7D is not unique in the way multiple focus points share parts of the same lines on an AF array. Most of the pro grade bodies and many of the pro-sumer and advanced enthusiast cameras that use an ever increasing number of focus points do the same thing.

The Canon 70D has 19 AF points. The D7100 has 51 AF points. You link to that answer because it explains the reasons for issues that you have with the AF. One such reason is the high number of AF points. Buying a camera with even more AF points does not sound like a good idea.

The answer further says:

Learning to harness and use these advanced focus systems, compared to the more rudimentary ones used in entry level DSLRs, is as large a step as learning the ins and outs of the metering systems and exposure options on a DSLR compared to a point and shoot.

You say

I got a Canon 70D a couple weeks

How many are a couple of weeks? How many photos did you take? You have to consider that it takes time and practice to get used to such an advanced AF system.

no matter how you look at it: When taking a picture of a person looking at you from a top view, ~6m away @55mm, 1/160, 5.6f you'll be lucky to get the face focused. Often times the camera will focus on the grass ground, if it's better lit/contrasted than the face. (The important thing about those settings is that since the face is 6m. away from you it will not cover the majority of any AF cross even if it's dead-center on)

I beg to differ. It matters a lot how you look at it. If anything, you example proves that the AF doesn't magically select the right thing, which is not too surprising. No photographer in his right mind would let the AF system pick an AF point automatically in a portrait situation like that. As the quote from the other answer rightfully claims: you really have to learn the ins and outs of the system. You have to work with it just like aperture or shutter and due to its complexity probably even more.

I'm not sure if this is a problem that you can solve by throwing more money at it. Sure, go ahead, Nikon (or Canon) will happily take it. But I wonder if you will be happy with an even more complex AF system.

Instead, make yourself familiar with the details and settings of the AF system of your camera. I remember that when they released the 1DX, which had a rather advanced AF system, they also released a booklet along with it explaining all the different AF settings. This goes to show that there is a learning curve to these AF systems, even for professional photographers.

Finally, to answer your question: Rent the camera. There's no other way fro you to find out if it works for you. If you don't like the AF system of the 70D and cannot work with it, don't go shopping based on spec lists or other people's opinions. Only you can till if the D7100 works better for you.

  • Thank you for your answer, however... 1- More AF points means each of them will have a narrower area from which to get the focus. Thus, more points: more precise autofocus. Meaning, if I center a face on the center AF point, the camera will have a narrower area on which to "guess" what am I actually pointing at. 2- a couple weeks since I got it, yes. Around 1000 shots taken already. Lots of them out of focus. And I read the manual from cover to cover. I know how the system works. It's just not consistent. (continues...)
    – MrMerrick
    Jun 29 '15 at 20:05
  • 3- I am not letting the camera decide. I set it to the center point, 1 point only autofocus. Is that letting the camera decide? No :) Even on a tripod, the camera will reacquire focus every single time I engage autofocus, which is ridiculous. 4- This is not about throwing more money, is about finding a consistent autofocus. Even if it's front or back focusing consistently, since I can fix that with micro adjustments. But this is absolutely random, by design. I'm merely asking if Nikon is somehow more consistent or predictable.
    – MrMerrick
    Jun 29 '15 at 20:09
  • @MrMerrick Then my answer really answers your question: rent the camera. There's no point in gathering more opinions. Some people might have the opinion that the 70D AF works for them. Some people might have the opinion that the 7100 AF works for them. But this is evidently not necessarily true for you. Your judgement sounds very biased. It sounds like you already made the decision. You are only looking for some kind of justification to buy that new camera. I gave it to you. It is what you want. Find out for yourself if it is what you need by renting and testing it. Good luck.
    – null
    Jun 29 '15 at 20:26
  • I'm merely asking to people who might have tested both. There is a point in gathering opinions, just as googling "autofocus 70d issues" yields some interesting results. My judgment is based on tests, not a bias for god knows what reasons (could you tell me which ones?). If you think I'm looking for a justification -or even fun- to trade (not buy a 2nd one) my expensive camera for a new one, waiting for it to arrive, testing, etc... boy, you really got the wrong idea. My question is for people who might have tested both cameras and have some true insight on both AF systems. Are you one?
    – MrMerrick
    Jun 29 '15 at 20:40
  • 2
    Note that "autofocus [insert camera model] issues" will generally get you a lot of complaints, for whatever camera model you choose.
    – mattdm
    Jun 29 '15 at 21:09

Okay, so, the fundamental problem, as discussed in the other question you've linked, is that focus "points" actually have to be areas, not literally points, and the camera can't know what you're actually interested in with that point.

However, if you're particularly interested in in-focus faces, there is a solution. That is: use a camera with contrast-detect autofocus (as found in "live view" in DSLRs and most mirrorless cameras) in combination with face detection.

By itself, contrast-detect AF suffers from the same basic problem — it tries to increase contrast within a given focus square, and that square must be more than just a point (by definition, really). But, since there's more data to work with, there's a magic bullet — the camera can detect faces, and decide to focus on those. In fact, recent models can specifically detect eyes and focus on them (some even letting you prefer left or right eyes). This solves the problem, because suddenly the camera knows to get the person in focus, not the zebra-striped tile that happens to be behind them.

Of course, contrast detect has a number of disadvantages, like generally slower speed, more difficulty in low light, and higher power drain. The good news, though, is that your 70D has this feature, and it even can use it in a hybrid mode which uses faster phase-detect in combination — this enables a face tracking mode which I've heard is very nice (I've never used this particular camera). You'll still need to use the rear LCD rather than the viewfinder, though, which can be awkward.

  • Yes, 70D's dual pixel contrast detection is awesome, I can vouch for that. Specially on video. However on the viewfinder, the problem is not that I can't focus faces. The problem is that whenever I want to focus on a target that doesn't completely cover an AF cross, if that target is surrounded by a better contrasted area (e.g. grass on a sunny day), the camera will then decide that it's the grass what I want focused, instead of that object. No matter how I place the object I want focused inside that AF cross, the camera will focus elsewhere most of the time. (continues...)
    – MrMerrick
    Jun 29 '15 at 20:53
  • In your question, you specifically give the case where a face is your focus target. With face detection enabled, the camera should successfully do that, even if the surrounding grass has higher contrast.
    – mattdm
    Jun 29 '15 at 20:57
  • This is why a 51 point AF system like Nikon's (or even higher like Canon's top of the line) can help, since the camera will have more areas covering a smaller space each. Thus being more precise, thus being more consistent. And that's why I'm asking to people who might have tested both. It seems ridiculous to me to be forced to use live view when a $1000 camera includes a viewfinder. It should work consistently. The whole concept of "areas" should be limited to an "area" AF mode, not the single point one!
    – MrMerrick
    Jun 29 '15 at 20:57
  • that was just a case I faced (heh) today. It's not about a face, it's about focusing what I want to focus. Even knowing how the system works and trying to anticipate it, it doesn't yield consistent results.
    – MrMerrick
    Jun 29 '15 at 20:59
  • More points might help, but they have to be an area because of their nature. But @null's point (no pun intended) really is valid: practice with the system and learning to work better with it can get you better results.
    – mattdm
    Jun 29 '15 at 21:00

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