Nikon D300 focus usage

[dmcantrell]

This is something that I've been struggling with for quite some time, and I'm -certain- that there's a solution...

On my Nikon D300, I typically use the back-button AF-on to enable focusing and continuous-servo AF. Also, usually I have the single-point AF mode enabled and I choose the focus point by using the multi-selector button with my thumb.

There have been many, many times when I'm out doing a shoot and the focus point "walks" around the viewfinder unexpectedly. Inevitably I end up missing a shot because of this. This usually forces me to put the multi-selector button on "L" to lock the movement of the focus points, but now I've lost the ability to quickly change the desired focus point and I end up framing shots weirdly.

I must be doing this wrong. Can anyone provide any guidance?

[shnitz]

There are two possibilities. You may be "fatfingering" the focus area selector with your nose or cheek. Or, you have dynamic area set up instead of single point area. This means you told your camera that you are shooting a moving subject, and you want some help tracking it, even though you are selecting the overall focus point. Read your manual for a more thorough explanation.

[RKEnnis]

I feel your pain! +1 on this question.

Currently I'm living with leaving the multi-selector button locked with the focus point in the center position most of the time. I'll occasionally unlock it and move the focus point to where I need it. For example, if I'm doing several similarly posed shots of a model I'll move the focus point. It's a pain that it's so fiddly to get it set back to center...

I too feel like I'm missing something.

[dmcantrell]

Originally Posted by shnitz

There are two possibilities. You may be "fatfingering" the focus area selector with your nose or cheek. Or, you have dynamic area set up instead of single point area. This means you told your camera that you are shooting a moving subject, and you want some help tracking it, even though you are selecting the overall focus point. Read your manual for a more thorough explanation.

Thanks for the reply. I can't tell you how many times I've read the manual to try to solve this exact problem. If I were to guess I'd say more than 15 times. I end up flipping back and forth through the manual trying to come up with a multi-dimensional matrix of the settings and the desired behavior...

There are lots of things in play here. There's the switch to select continuous-servo vs single-servo. There's the selector switch to pick single-point / dynamic-area / auto-area (which I have on single-point). There's the custom-setting a8 (AF point selection). There's the AF-on button, and the focus point illumination setting.

I hadn't considered that my nose might be moving the focus point. That's something I'll test out next time I'm out.

How do you have yours set up?

[RKEnnis]

Clearly what is happening to me is that I'm inadvertently moving the selector. I just don't know how to avoid that other than locking it.

In your original post, it sounds like you're complaining that you're missing shots because the focus point selector ends up in the wrong spot. Do the other settings, such as AF-C vs AF-S or single point vs dynamic area really have anything to do with it?

Maybe I'm misunderstanding your question...

[dmcantrell]

Originally Posted by RKEnnis

Clearly what is happening to me is that I'm inadvertently moving the selector. I just don't know how to avoid that other than locking it.

In your original post, it sounds like you're complaining that you're missing shots because the focus point selector ends up in the wrong spot. Do the other settings, such as AF-C vs AF-S or single point vs dynamic area really have anything to do with it?

Maybe I'm misunderstanding your question...

Well, I'm not sure how to answer your questions because that's why I'm asking.

Here's the way I understand it:

AF-S will attain focus (and beep if that's set up), and will remain static until the shutter is released.

AF-C will attempt to continuously attain focus. Since I use the AF-ON back button, I can control this somewhat by toggling my thumb on the AF-On button. I assume that this "continuously attempt to attain focus" is adding to my difficulty. The manual states that, when using this AF-C mode, the camera will enable "predictive focus tracking" when the camera thinks the subject moves.

The custom setting a8 tells the camera how many possible focus points is can use, and the custom setting a3 tells the camera how far to look around the selected focus point if it decides that the subject has left the selected point. However, this only affects the situation when the dynamic-area AF is chosen.

The behavior that I'm complaining about is this :

* I have my eye in the viewfinder, camera against my face.
* I have my thumb on the AF-ON button.
* The subject (let's say a baby in this case) is moving around erratically in the frame, and I'm trying to keep her eye in focus and wait for that heart-melting smile shot.
* Just as she smiles, the focus point "walks" across the screen (I still have the AF-ON button pressed) and ends up on her foot or something, and when the shutter is released her foot is in sharp focus and her face is not.

I just have to think that I'm not using the system correctly.

[shnitz]

It really sounds like you're hitting the focus selector with your face, as your settings sound solid. If you have single-point AF instead of dynamic, then the selector won't move until you tell it to move. Hold the camera differently, or start using the lock switch.

[RKEnnis]

I agree. If you're actually seeing the focus point reticle move just as you're shooting, it pretty much has to be that you're moving it inadvertently. I'm not sure what you could do to avoid this, other than change the way you hold the camera.

As I said, I have the problem of the reticle moving accidentally, but it's usually while I'm holding/carrying the camera, not while I'm actually shooting. I've gotten in the habit of just leaving the lock on, unless I really need to change the focus point.

Anyway, if you AREN'T seeing the reticle move, but the focus point in your images isn't where you expect/want it to be, then you need to look further at your settings...

[dmcantrell]

Thanks a lot for the help guys. This has been useful. It's difficult to glean these subtle nuances from the documentation.