d750 focus accuracy?

Discussion in 'Nikon' started by dylan_park, Nov 15, 2016.

  1. I am looking to get opinions on the d750 and auto focusing, related to how fast but more so how accurate. I was looking at a canon 5d mark III which has more cross points, though is the nikon reliable when it comes to this, as how many shots come out well focused makes a big difference. My key focus is fashion and potraits, with occasional movement.
    Thanks
     
  2. I find the D750 autofocus accurate, fast and decisive, even in low light, particularly with AF-S lenses. In light suitable for what you're doing, I can't imagine your having trouble. I did a portrait session Monday with the old non-AF-S Nikkor 85mm f/1.4D, and one shot out of 90 was out of focus. What could be a concern is the D750's relatively small buffer, which can cause burst shooting to slow down significantly once it fills.
     
  3. oh that's encouraging great to know. i am in the process of getting one.. i think though this is important
     
  4. Dpreview has some videos of various cameras trying to
    lock focus in low light. The outer points of the D750 (and
    all multicam 3500 variants) aren't cross type, but so long
    as you have some detail in the right orientation the D750
    is extremely good, if not up with the latest module in the
    D5. The D750 AF points are clustered a bit more closely
    than the other FX bodies though, which may slightly
    affect you if you like to focus off centre (but there's not
    much in it).
     
  5. If using single point focus through in afs, and moving over eyes even to right or left of frame is that an issue, or even recomposing?
     
  6. The D750 AF is very good. I didn't notice any significant accuracy issues with it, though like with every camera, I do use autofocus fine tuning to adjust the camera to the lens. After this process is complete, I found the AF very reliable. Most of the time I used this camera with the VR 24-70/2.8E and VR 70-200/2.8G II. The 5D Mark III does have a broader coverage of cross type points so if you use far off center points (along the long axis of the frame) it may work more reliably than the linear points of the D750. Nikon has extended the cross type point coverage in the D5 and D500 but the D750 and D810 have not yet been upgraded with this new system. However, the D750's AF system is still very good as long as you're happy with the area of the frame that the AF points cover.
    The body ergonomics between the D750 and 5D Mk III are quite different; I would recommend trying them out to see which you're more comfortable with. The D750 is a bit on the small size for my hands, but I'm probably in the minority.
     
  7. Very interesting, it seems like if i want to be working in rule of thirds with enviromental fashion or other forms of composition, that this may not actually be the camera for me.
     
  8. If using single point focus through in afs, and moving over eyes even to right or left of frame is that an issue, or even recomposing​
    This is very subjective, a lot depends on what lens, at which distance, in what type of light, and even the colour of the eyes has some influence, not just for the D750, but for any camera
     
  9. I'm with C.P.M. - on any 24MP body at a wide-ish aperture, the issue is that you're focussing in one place and then, when you rotate, the point you chose to focus on is no longer on the image plane. At telephoto and moderate aperture you may not notice, especially at lower resolution (I say telephoto because you can't turn the camera very far and still have the subject in the shot anyway). At, say, 35mm f/1.4 I'd expect this to be extremely visible. It's a function of being able to capture detail and the geometry of the scene, not the AF module - except in the case of Hasselblad, who have a single AF pointt but adjust the focus distance with an accelerometer when you focus-and-recompose. This has always been the case, but the amount of detail captured by older optics and 35mm film meant that it may not always have been terribly visible.

    If you have fairly wide AF coverage, you can focus with the nearest AF point, and rotate slightly - then the error should be quite small. The biggest problem then is if your subject isn't holding totally still (which would be a problem with AF-S anyway - it'll lock as soon as it sees focus, and if you or your subject sway slightly before the exposure, the focus will be off). Personally I use AF-C with the AF-On rear-button focus, keep focus tracking until the last minute, and if I need to recompose take my thumb off as near to the final exposure as possible. With 3D tracking this does mean you can focus in the middle and rotate the camera, and the AF should track across the AF sensor until it reaches the edge, adjusting the lens focus as it goes. Or you can just move the AF point manually with the multi-controller.

    As Ilkka says, the newer cameras have slightly wider AF coverage, and the D810 is very slightly wider than the D750, but you can get very close to the rule of thirds points with any of these - probably close enough, so sorry if I've scared you with my talk of the D750. If you want AF much nearer to the edge of the frame you have to go mirrorless (or use live view on your dSLR - or use Canon's dual-pixel on-sensor PDAF thing): the geometry of the mirror means that no SLR can get phase-detect autofocus near the edge of the frame. On the other hand, DSLR AF tends to work better in low light and be faster, and you have the advantages (and disadvantages) of an optical viewfinder. Choose your poison. :)
     
  10. the geometry of the mirror means that no SLR can get phase-detect autofocus near the edge of the frame.
    Well, DX DSLRs do have AF points right to the (short) edges of the frame (especially D500) but the FX cameras don't. Still, I find with the D5 that the outermost columns are close enough to the short edge and often I have to avoid the outermost columns to avoid part of the subject being cropped out. However, neither FX nor DX cameras have AF points very close to the long edge of the frame.
    Many mirrorless cameras that do support PDAF don't cover the frame to the edges with PDAF points, either, but the points can be closer to the edges than in most FX DSLRs.
    Rule-of-thirds (or the golden rule, which the rule of thirds is an approximation of) should not be a problem though, even with the D750. However, you may end up using the linear points more than you'd like. I guess the only way to be sure is to try out these cameras and see how you like working with them. Do give the D500 a try also. For me the D5's extended coverage is a big improvement. Perhaps the Multi-CAM 20k system will be included in some new FX models in 2017.
     
  11. Ah, Ilkka is right. Sorry, I should have said no full-frame camera with a conventional flange distance can get AF point out to the edge of the frame; it's true that a DX camera (which has a deeper mirror box than it strictly needs - hence Canon's EF-S lenses which stick into the mount) has the image "shrunk down" to the area the AF can cover. Of course, you don't then quite get the accuracy of placement - the same AF points are covering a larger portion of the frame. Again, pick your poison. I imagine you could get full-frame shooting with wider AF coverage if the mirror box was substantially deeper than the F or EF mount, but it would make life harder for a lot of wide-angle lenses.

    It's true that nobody does PDAF all the way to the edge even in mirrorless. The angle that light is falling on the edges of the frame from the far side of the aperture is quite extreme, so I suspect there's a point where it gets impractical - but at least the mirror isn't a problem, and you can always contrast-detect.

    I think rule of thirds is right at the edge of the MultiCAM 3500 region? I seem to need some wiggle room sometimes. I'm certainly looking forward to the 20K arriving in a D8x0 successor - along with sice software features like automatic AF fine-tuning.
     
  12. I have been going back to try out old early autofocus cameras for the last several years (e.g., http://www.photo.net/modern-film-cameras-forum/00b7pQ with other links there).
    Even the very early AF systems proved to be more than adequate. In the applications you mention where I would imagine you are operating pretty close to the subject, I would be surprised if it were really worth worrying about AF, especially since so many modern systems allow manual 'touch-up' for you to control what YOU, as opposed to any automatic system, want in sharpest focus.
     
  13. JDM: I may have been happy with the AF on my F5 or Eos 620, but I do think demands have got higher over time. I trusted the AF on my D700, but it effectively had quite a deep depth of field because of the low sensor resolution and strong AA filter. I get more misses with me D810 (although not so many as with my D800) at wide apertures; I don't think this is because the AF module is worse, it's because I can actually see when I've missed now. I do believe the D750's AF is likely good enough (and the sensor is a little less demanding than a D810), but I'd be concerned about this factor in focus-and-recompose (which I did all the time in my Eos 300D 6MP days). Of course, this assumes that a) you're pixel-peeping, and b) that you're using a fairly wide aperture. "f/8 and be there" and don't look too closely at the result, and it won't matter - I'd rather get a slightly soft shot than none at all.
     

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