Weird D7000 experience

[michael_b10]

<p>Last night I took my D7000 to a small outdoor concert - basically three guys playing on a lawn, lit by a couple of stage lights propped up on cinder blocks. I put on my 50mm 1.4D, which has always focused perfectly on this body at every aperture (I have had to fine tune a couple of zooms). I took a few shots of the band that came out alright, considering the conditions - maybe there was a bit of motion blur, maybe focus a tiny touch off due to shallow DOF if the singer moved one direction or the other - but all in all within what I'd consider to be an acceptable margin of error. But then, at a certain point, which coincided with me changing the angle from which I was shooting, every single shot became WAY out of focus - or to be more precise, exhibited severe backfocus. The singer is completely blurry, but the amp a couple of feet behind him is remarkably sharp. Shutter speed was 1/640 sec, so it wasn't a matter of blur (especially since the amp is so sharp you can read the small lettering on it). Tried AF-S and AF-C. I wondered if something happened to my set up to infuse backfocus into my system, so a few minutes later I took a few shots of my dog in the back of my truck, lit only by a gas station light, then went home and shot a few things in a very dimly lit kitchen - all were on the money. I've been in similar situations to the concert many times with my D90, and have never had anything like this kind of experience. I'm fairly sure I wasn't lunging forward as I pressed the shutter to create the backfocus effect with shallow DOF. Frankly, I'm at a total loss as to what happened, and am mildly disturbed by it because in so many ways the D7000 is such a remarkable camera, but I'm not sure how much I can fully trust it in a pinch. And I think I would have gotten much more consistent results with the D90. Anyone else had this kind of thing happen, or any idea what might be up? </p>

[dbcooper]

<p>AF-S or AF-C is probably less important for this situation than the AF-Area mode or the focus point you selected. The camera probably chose a focus point it could achieve focus lock with. It helps to understand how the various focus points on your camera work (i.e. not all of them will detect vertical <em>and</em> horizontal edges to focus with), and what they're detecting (i.e. edges or contrast) to get AF lock.</p>

<p>In this kind of situation, I often use a single focus point, get focus lock, recompose, and shoot, but that's just how I do it...there are other useful techniques, especially if you're not constantly varying your shooting distance. I'm sure others will chime in on the subject. HTH.</p>

[michael_b10]

<p>All shots were single-point AF-S or AF-C either single or 9point. With this kind of situation I was focus locking but not recomposing due to shallow DOF - I simply chose the focus point over what I wanted to focus on, locked focus, and released shutter. The points I was choosing were not cross-type sensors - they were outer focus points - but I thought I was working with a subject with enough contrast that it wouldn't matter. Maybe not? Could lack of cross-type create such pronounced and spontaneous backfocusing?</p>

[dbcooper]

<blockquote>

<p>Could lack of cross-type create such pronounced and spontaneous backfocusing?</p>

</blockquote>

<p>Not necessarily backfocusing, but maybe what they were <em>able</em> to focus on happened to be behind the subject. This might help you narrow it down: http://www.bythom.com/autofocus.htm</p>

 

[rodeo_joe1]

<p>I've never trusted multiple focus points. I find it much quicker to set a single central point and recompose after the focus is locked. At least you know exactly where the focus point is with this system.</p>

<p>Actually I admire anyone who's got a quick enough thumb action to steer the focus point to the right spot while maintaining the composition they want!</p>

[michael_b10]

<p>It's often quite easy to set up the focus point in advance, unless you're dealing with a fluid, fast-moving situation. (Sometimes even with a fast-moving situation, it can be really helpful to use a point other than center-point, IF you can predict where in the frame the action is going to happen.) And if shooting shallow depth of field, it's a good idea to recompose as little as possible, since sometimes the act of recomposing shifts the focal distance just enough to throw your subject out of focus. Shooting f8 it doesn't matter. Shooting f1.8 it can. You can set the camera up so the focus point is always illuminated, so you always know where it is; if you want to see where it is before you put the camera to my eye, you can check the lcd. So, for me, anyway, i find selecting points other than center helps me get the shots i want. </p>

[CvhKaar]

<p>Michael,<br>

If you open the pics in Capture NX2 or in VIEWNX 2, and you swith on the "Show Focus Point' ( not sure what its called in the English version of those programs...) it shows with a little red rectangle the focus points used.. , this should show you what the camera was actually foccusing on, and this should then also be th "Sharp Zone"...</p>

[michael_b10]

<p>Thanks for the ViewNX2 tip - I usually just use LR3. I did what you suggested and for those shots that struck me as weird, well, it's weird - the focus point is right where it was supposed to be. On some other shots, though, the focus point was definitely not quite on its intended target - which could be user error, or just lack of precision in the AF system, in that it can't always read my mind. In finally downloading my card into my computer, I'm actually quite impressed with how many shots came out well in such poor light - it was only shooting from that one particular angle that for some reason was strangely problematic.</p>

[chris_weller]

I'm having a very similar problem - see my post here

 

http://www.photo.net/nikon-camera-forum/00Yu54

 

 

Thoughts