Group focus question

<p>Hi folks. <br>

First let me say that I love the group focus feature. I am perplexed as to why Nikon does not offer it via firmware upgrade for the D7200 as it has the same focus module as the D750.<br>

Here is my question. I do not know if I just noticed this or it has been there from the get go. When I shoot with my D750 I can see the 4 focus points through the view finder. 5 are active as the center one is invisible, but usually that is the one that hits. I know this because when I chimp, I can see the single focus point that hits. Most of the time it is dead center between the four I can see in the view finder. Other times it is one of the other four, but I know which one hit.<br>

-<br>

With my D500, I can see all four focus points through the view finder, same as the D750, but when I chimp those pictures, I have no idea what focus point hit, because I see all FOUR, unlike the D750.<br>

I looked through all the menus and have no idea how to make it like the D750. Any help would be greatly appreciated.<br>

Thanks javier</p>

 

I can't help you with making the cameras match,

but I'm wondering why you use group focus at all?

A lens can only focus on one plane and, as you see

by reviewing, only one focus point gets truly sharp

focus. So if the centre AF area is nearly always the

one that "hits", why not set the camera(s) to use just the centre point? And that way you know exactly where the camera's going to focus, rather than leaving it to chance.

 

 

Canon tried offering a focus mode where multiple AF points were linked to the aperture in order to make the depth of field deep enough to cover the subject. However, you then lose control of both aperture and focus plane to the camera, and that mode didn't prove popular with photographers.

When using a single point with a longer lens to track a moving subject, it can be hard to

maintain the one point exactly on the same part of the subject all the time. Group AF uses pattern recognition on the

cameras with high resolution RGB matrix meters to compensate for slight variations in subject position in the frame by selecting one of the adjacent focus points to focus while the center of the five is no longer squarely on the subject. It

works extremely well in my experience. The D7200 has a low resolution matrix meter which doesn't support group AF.

<p>RJ: I was disappointed when Canon got rid of their A-Dep AF mode, not that I've bought a Canon DSLR since (because I'd hopped to Nikon by then). While it had a limited amount of control, it did try to spread the midpoint of the AF across several subjects and - more importantly for me - light up all the AF sensors that thought they were in focus, which (with limited accuracy) was really useful for focus with a tilt-shift lens, especially on a camera with a pentamirror. Nikon do the same thing in auto-area autofocus, but for some reason don't make it work when you're in manual focus mode (unless you use a dandelion chip on a manual lens and the camera thinks it's autofocussing). The tilt-shift argument is why I've wanted a 4-way live view split - but I'll take the 2-way split on the D810 as better than nothing.</p>

<p>Thanks a bunch Rodeo Joe for the response. </p>

<blockquote>

<p> I'm wondering why you use group focus at all?</p>

</blockquote>

<p>For those that have used it and have given it a chance, I am willing to bet that most would love it in its proper context. At first I used it for my grand kids soccer games and it rarely if ever missed. I then started to use it for street and it became most useful especially for those ''decisive moments''. Point and shoot. It rarely misses as one only needs to be close. If you shoot birds or wildlife, most any sports, this is a must.</p>

 

<blockquote>

<p>A lens can only focus on one plane and, as you see by reviewing, only one focus point gets truly sharp focus. So if the centre AF area is nearly always the one that "hits", why not set the camera(s) to use just the centre point? And that way you know exactly where the camera's going to focus, rather than leaving it to chance.</p>

</blockquote>

<p>I do depending on what I am shooting. Portraits, macro etc. </p>

<blockquote>

<p>Canon tried offering a focus mode where multiple AF points were linked to the aperture in order to make the depth of field deep enough to cover the subject. However, you then lose control of both aperture and focus plane to the camera, and that mode didn't prove popular with photographers.</p>

</blockquote>

<p>I know nothing about Canon, but I have read that it did not perform any place near the Nikon product.</p>

<p>Thanks for the comments Ilkka<br>

</p>

<blockquote>

<p>When using a single point with a longer lens to track a moving subject, it can be hard to maintain the one point exactly on the same part of the subject all the time. Group AF uses pattern recognition on the cameras with high resolution RGB matrix meters to compensate for slight variations in subject position in the frame by selecting one of the adjacent focus points to focus while the center of the five is no longer squarely on the subject. It works extremely well in my experience. </p>

</blockquote>

<p>Agreed and yes, it works very well. Super fast. It rarely misses.<br>

<br>

</p>

<blockquote>

<p>The D7200 has a low resolution matrix meter which doesn't support group AF.</p>

</blockquote>

<p>This explains it. I did not know or consider this. Thank you !</p>

<p>Andrew. I thank you very much for the comments.</p>

<blockquote>

<p>RJ: I was disappointed when Canon got rid of their A-Dep AF mode, not that I've bought a Canon DSLR since (because I'd hopped to Nikon by then). While it had a limited amount of control, it did try to spread the midpoint of the AF across several subjects and - more importantly for me - light up all the AF sensors that thought they were in focus, which (with limited accuracy) was really useful for focus with a tilt-shift lens, especially on a camera with a pentamirror. Nikon do the same thing in auto-area autofocus, but for some reason don't make it work when you're in manual focus mode (unless you use a dandelion chip on a manual lens and the camera thinks it's autofocussing). The tilt-shift argument is why I've wanted a 4-way live view split - but I'll take the 2-way split on the D810 as better than nothing.</p>

</blockquote>

<p>It sure seems that Canon is clearly behind Nikon in both Focus speed and accuracy. Atleast that is what I read online. </p>

<p>It is difficult to judge autofocus performance of different cameras as each user has their own way of working and their subject matter and the lens and lighting conditions play a role as well. I have not used Canon DSLR equipment (except briefly a few times) so it wouldn't do any good for me to comment on Canon's AF, but occasionally I shoot events with a friend who uses Canon and from that my feeling has been that the two systems are comparable in autofocus ability.</p>

<p>Dpreview sometimes comment in their articles that Nikon's subject recognition and tracking system (3D tracking) works better when the subject moves across the frame than Canon's equivalent, and this may be true, but I usually restrict the AF point selection to a narrower area and juggle it about as needed. The D5 and D500 have received a lot of favourable comments for their AF and my experience with the D5 is that it is a major improvement especially when focusing moving subjects in dim light or with low contrast subject matter. I've obtained very high keeper rates with rejects only a few shots in a hundred (with e.g. the 24-70/2.8 E, in lighting conditions requiring about ISO 8000, 1/500s, f/2.8). The camera can also handle f/1.4 lenses well. Compared to previous generation Nikons, the AF array was extended in the direction of the long axis and they put in more cross type points which make full body portrait shooting in vertical orientation easier. (In the D500 of course it covers an even larger part of the frame.) I believe Canon has also made improvements in their 2016 models, including broadening the spacing in the AF array along the short dimension of the frame.</p>

<p>On the other hand, Canon has "dual pixel AF" that can be used with live view and video, and in the latest cameras it seems to work very well and can follow a moving subject effectively and by just touching the screen, you can switch between subjects in a smooth and nice looking way. There are some example videos online, e.g.</p>

<p>http://blog.jonroemer.com/2016/06/rodeo-sunset-canon-1dx-mark-ii-test-run/</p>

<p>https://www.youtube.com/watch?v=z0If-yw2AOI</p>

<p>Nikon doesn't have really good continuous autofocus during live view or video in their DSLRs which means that if you want to focus during the video recording, it may be necessary to use manual focus (which in turn works best with manual focus lenses, which fortunately are in abundance for the F mount, but you still need a way of seeing which part is in focus, and there is no zooming of the LCD image possible during the recording itself). A loupe for the LCD or an external screen may be required in some cases. Nikon does have nice video autofocus in their 1 series system but it would be nice if they can incorporate something like it into their larger sensor cameras (DSLRs).</p>

<p>Also keep in mind that Nikon introduced the D4S, D810 and D750 in 2014, before the D7200 (early 2015). The D4S, D810 and D750 all have Group AF. If they could have put that feature in the D7200, Nikon would have done so from the beginning.</p>

<p>I like using Group AF for photographing e.g. hummingbirds feeding on flowers. Hummingbirds tend to move around a tiny bit while feeding, and Group AF does a fine job adjusting to those slight movements.</p>

<p>However, Group AF doesn't work as well for more general birds in flight. As soon as the bird is not positioned directly within the group area, AF falls apart completely. For fast moving birds, it is difficult to keep them within a small area inside the frame. I would rather use 9, 21, or 25 point AF, depending on the camera or even Auto Area AF on the D5 and D500 for general birds in flight in the sky.</p>