Why would I want to have more than one AF point?

<p>I sometimes use a camera with only one autofocus point and sometimes one which has 7 AF points. However even on the 7 AF point camera I always only select the center one and simply switch the others off. So I always focus and then recompose when applicable, and am happy with this.<br>

Now I noticed that the higher-end a camera gets, the more AF points it has, so having more than one AF point is apparently desirable.<br>

However I fail to see how it can make sense to have more than one AF point. I feel that any additional AF points just get in the way.<br>

Do you use more than one AF point normally? Why would I want to have a camera with more than one AF point?<br>

--<br>

I shoot 35mm film on EOS 620 and EOS Rebel.</p>

<p>Multiple AF points are useful during composition of the photo, when movement of the camera (focus, recompose) might not be desirable. They are also useful for tracking moving objects like the AF options found in higher end cameras while shooting sports and wildlife. I mostly use one AF point, but that point is quite frequently not the center of frame.</p>

<p>If you use autofocus and if the subject is moving towards the camera, and if you don't want a centered composition, then having multiple AF points is very useful. An alternative is to use the center point and then crop to reframe the image, but you may end up with a lower quality image this way, depending on how much you have to crop to get the composition desired. In practice I use both techniques at the same time as my cameras do not have AF points in the outer parts of the frame. Even if you have a relatively static subject, the depth of field at very wide apertures can be such that it is better to use a peripheral AF point than center point and recompose. In practice the central AF points in most cameras work significantly better than the outer points so the choice is not clear-cut. E.g. Canon 5D Mk III and 1D X have cross type AF points at the outer rim of the AF sensor array and this should make it easier to get good results using them.</p>

<p>When I used early AF SLRs that did not support multiple AF point, I basically found manual focus preferable as using MF I could just focus on the matte screen at any point and I didn't have to any of this juggling to move the AF point around or to focus and recompose. However, most modern cameras have focusing screens which do not lend themselves well to manual focus of wide aperture lenses, thus this approach has become more difficult (and less reliable) than it was e.g. with my F3HP in the 90s. </p>

 

<blockquote>

<p>An alternative is to use the center point and then crop to reframe the image, but you may end up with a lower quality image this way, depending on how much you have to crop to get the composition desired.</p>

</blockquote>

<p>Another alternative is to lock the center point focus and recompose before releasing the shutter, called "Back Button Focus".<br>

<a href="/beginner-photography-questions-forum/00bsbr" rel="nofollow">http://www.photo.net/beginner-photography-questions-forum/00bsbr</a><br /> <a href="http://improvephotography.com/4552/back-button-focusing/" rel="nofollow" target="_blank">http://improvephotography.com/4552/back-button-focusing/</a><br /> <a href="http://digital-photography-school.com/back-button-focus" rel="nofollow" target="_blank">http://digital-photography-school.com/back-button-focus</a><br /> <a href="http://www.zachandjody.com/blog/tuesday-photography-tips-tricks-back-button-focusing/15588/" rel="nofollow" target="_blank">(link)</a></p>

The focus and recompose method can produce focus errors with fast lenses

used wide open, especially up close. But if your fastest lens is f/2.8 or

slower you may never notice the slight focus shift.

<p>It doesn't begin or end with just one focus point.<br>

Here is part of the <a href="http://en.wikipedia.org/wiki/Canon_EOS-3">Wikipedia</a> article on the Canon EOS-3 FILM camera of <em>1998</em> (sold until 2007).</p>

<blockquote>

<p>The EOS-3 introduced the <em><strong>45-point</strong></em> [emphasis added JDM] autofocus system later used in the EOS-1v, EOS-1D and subsequent Canon professional SLRs. It was the last camera outside the 1-series, either film or digital, to receive Canon's top-of-the-line AF system until the March 2012 announcement of the EOS 5D Mark III.</p>

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<p>This is a remarkable camera and I must not be the only one to find the complex focusing system to approach magic in operation. I can set the little dear on autofocus and shoot away with abandon and get wonderfully focused images. When I want to take full control, I focus manually and use none of the AF points at all.</p>

<p>"Why would I want to have a camera with more than one AF point?"<br>

<br /> Well, look at it another way. On some of the new cameras, say the Nikon 1, it has something called Face Recognition.<br /> <br />As soon as the camera "sees" a face in the composition the focus starts tracking it. So, regardless of how you place the person in the frame the focus will lock onto the person's face as soon as you press the shutter halfway.<br /> <br />Now, with only one AF point this wouldn't be possible.</p>

<blockquote>

<p>Why would I want to have a camera with more than one AF point?<br /><br /><br>

</p>

</blockquote>

<p>Two rather contrary thoughts came to my mind:</p>

<ul>

<li>Why would I want AF points when I can manual focus?</li>

<li>Why would I want AF points when I have face/touch detection focus?</li>

</ul>

 

Face recognition will only get better. More - and more precise - focus

points will enable eye recognition to ensure sharp focus even with fast

lenses used wide open on the point most viewers associate with

satisfactory focus. Same with tracking to maintain sharp focus on the

eyes with moving subjects and/or handheld cameras.

<p>Very fast lenses can be difficult in AF and MF is not great on modern bodies designed for AF (except using a tripod an live view). Very fast lenses can have a DOF at portrait distances that is just over an inch. The shallowest DOF lenses I have used for this purpose are the Canon 85 F1.2 (a great lens) and a Fuji 180 F3.2 (the 6x8 camera gives a shallower DOF). The Canon 300 F2.8 used for portraits is actually slightly shallower DOF but I rarely use this lens. In Macro work as well DOF can be very shallow. In general manual focusing is best in these situations but modern DSLRs are not great unless you use Live view. If the subject is off centre then you can focus and recompose - this is the approach I usually use and in general there are no issues so long as there is no subject movement any your DOF is not ultra shallow. You can also use an off center AF point but I tend to use this approach only when taking a sequence of shots as selecting a different AF point can interrupt the flow. Of course this approach is helped if the AF points on the camera cover a wider range in the viewfinder.<br>

Face detection is usually fairly crude AF that is designed for camera that either have small sensors (e.g. the Nikon 1) or with kit zooms that are quite slow and thus have a very wide DOF. To illustrate the point lest compare the Canon 5DIII and 85 F1.2 with a Nikon 1 and 10-30 zoom with a subject distance of 2 meters (the Nikon 30mm lens and small sensor give a very similar angle of view to the 85 on the full frame Canon). The Canon has a depth of field of only 4cm whereas the Nikon has a DOF of 56cm due to its smaller sensor and slower lens. Thus the task of the AF system is much easier.<br>

The other big use of multipoint AF is for action sports. In this case the camera needs to be in an AF tracking mode (on Canon this is called AI Servo). in order to keep a rapidly moving subject in focus (especially if it changes direction relative to the camera) takes a bit of practice. The essence is to keep the AF point centered on the subject so the camera has the best chance. This takes some practice and by expanding the AF point (Canon offers a number of modes on the 1D series, 5D bodies and 7D - I am not sure about lower down the range as I have not really used these bodies). This AF expansion gives you a greater chance of keeping the AF point on the subject and getting a better hit rate. I shoot a lot of winter sports and find that this approach works well when the light is not great and subject movement rather erratic.<br>

AF is not quite as accurate as the manufacturers would have you believe and there is a trade off between speed and accuracy. In general a phase detection AF is the fastest but contrast detection slightly more accurate. Of course this varies widely between bodies and largely depends on what you spend. For action sports you cannot beat a good AF system like the Canon 1 series bodies. As someone who shot action sports with manual focus film cameras I can tell you it is much easier these days. For portrait and Macro use I still find manual focus the way to go. On an SLR or similar this means using live view, a tripod and zooming in. For portrait use this is not usually convenient so in general I will use AF with a DSLR (although by changing the focusing screen you can get easier MF). The most accurate 35mm system for portrait use is still the rangefinder approach but it takes practice and can be slower than an AF system.<br>

The test of AF accuracy may be of interest<br>

http://www.lensrentals.com/blog/2012/07/autofocus-reality-part-1-center-point-single-shot-accuracy</p>

<p>For sports and wildlife shooting multiple AF focus points are useful when a lot is happening at once, and you're shooting the scene in general as opposed to focusing in on a single player, vehicle, etc. You don't tend to have DOF issues especially with longer lenses, but you do want to get some part of the photo in sharp focus. If you can get multiple focus points at once then you'll have an overall sharper outcome.</p>

<p>99% of the time I use the center AF point. It's nice to have the option of using the others, but for me it's far from essential.</p>

<p>I just purchased another D7100 and figuring out to change to just one auto focus point is not readily evident and even hard to find in the manual. I've set up the body so I can select one auto focus point from among 51 so I have plenty of focusing/composition options. I also do not understand why someone would want to use more than 1 auto focus point simultaneously because the body may not focus on the subject you want it to focus on. </p>

<p>99% of the time I'm set to single auto-focus point, usually the centre, and spot metering, and then recompose. It's second nature. I don't often shoot moving targets and old habits just die hard, I guess. In the past when I've been tempted to deviate I usually give myself a shake and stick to the tried and true. It keeps my results consistent, like a Big Mac. Not necessarily a good thing... but no surprises.</p>

<p>Multiple focus points are pretty handy when shooting birds in flight!</p>

<p>I agree with BIF, but you have to be very careful. If I use all 63-points on my 5D MkIII, I'll often get a perfectly focused wing but an OOF eye. Single point avoids this, but some of the faster birds, like ducks, can be very hard to keep one point on the head or eye. I typically use 1-point expanded, which is like a total of five points in a small area.</p>

<p>Michael, I had the same problem when I first got my D7100. Look on page 74 of the manual. Push in the AF mode button on the camera and rotate the front "command dial" so that a 5 is shown on the top screen. With the button pushed, rotate the back command dial so that "AF A" is shown. Now you are in center point focusing.</p>

<blockquote>

<p>99% of the time I use the center AF point. It's nice to have the option of using the others, but for me it's far from essential.</p>

</blockquote>

<p> <br>

Ditto. Moving from point to point is distracting and time consuming. Every time I compose a new frame I have to worry about where the focus point is.<br>

<br>

Besides, with full frame cameras, the spread of the autofocus points isn't wide enough to make a big difference in subject placement. If I need to focus near the edge of the frame, I prefer to used Live View (motionless subjects only).</p>

For the way I shoot, I'm mostly center point. The other times, all points. Nice that pressing the button

inside the controller will toggle AF to the other state...

<p>I would like to consider a little different question:</p>

<blockquote>

<p>Why would they make many AF points?</p>

</blockquote>

<p>Because sometimes, it is not good to use single AF point, which means the "focus and then recompose" technique is not good (sometimes). The reason is that technique is (sometimes) too slow and/or too inaccurate. In the early days (like in the Maxxum 7), they have many AF points but the photographer chooses the point, but that way may be too complicated and too slow, so they make it automatic now (but this way is not smart enough).</p>

<p>An alternative is using manual focus, but this method requires a very good viewfinder (and good focusing screen) and trained eyes</p>

<p>Those who use center focus point only (or the majority of the time) and without recomposing or cropping later must live a charmed life. The critical focus points of their images are always at the center. Rule of the third and golden mean need never apply.</p>

<p>But they won't end up with photos like these:<br>

<br /> http://www.photo.net/photo/8353098<br /> http://www.photo.net/photo/17536945<br /> http://www.photo.net/photo/17527838</p>

<p>Robert, you can move the single point around. It doesn't have to be center-point.</p>

<p>David - I think the point of multiple AF points is that you don't need to move it around if you have all, or many AF points enabled. You know what's in focus across the composition without moving the camera up, down, sideways, or resetting to one of the "non-centre" points. As I alluded to in my earlier post it's more information about the photo before you take it. And I totally agree with Robert K - all photos are not about having the center focused. Some, perhaps many, are - but I like to have information about the rest of the composition as well.</p>

<p>If there's an important element to get in focus, for instance the eye, then you need to move the AF point around, or focus and recompose or use multiple AF points, but manage them with the joy stick. Turning all on, and using shallow DOF, is a recipe for disaster.</p>

<p>I shoot at f1.2 and f1.4 pretty much all the time.<br /> Once I started really concentrating on using all the AF points my focus improved incredibly.<br>

If I was an f22 landscape shooter center would be enough.</p>