I just got my D7000 today with a new lens (18-140mm//3.5-5.6) and am still trying to get all my settings put in but have been really frustrated with the autofocus, especially when it comes to using the flash.
I was shooting in manual mode at 1/160, full open with ISO 800 - I tried with both the pop-up flash and my SB600 and had the same result.
I've had my D5000 for 3 years now and loved it but felt I had outgrown it but wasn't ready to invest in full frame yet. Now I'm scared I made a bad choice and am convinced I must have a setting wrong.
The autofocus doesn't work any differently when you are using the flash. Of course, there's generally less light then or you wouldn't be using the flash. Still, it shouldn't be a problem. (I'm assuming you are using the viewfinder, not Live View mode.)
When you say it's "slower," can you be a bit more specific as to what's happening? Is it "hunting" back and forth? Is the subject in focus when the shot is actually taken? Posting an example image might be useful, too.
I would have thought the same thing as you that the flash shouldn't affect the speed and abilities of the autofocus, but I tried it in both auto and manual and had the same result. That's why I wanted to sign up for a forum to ask the question... I was starting to think I was crazy.
I retried this morning while the house is brighter, same settings as above, it had a pretty quick response but as soon as I put on the pop-up flash it took longer to go from the time I pressed the button to the time it locked in and took the picture.
As I've been thinking about it I'm not sure it's the autofocus... I don't really have examples because it's not showing up in the pictures, it's more while I'm taking it. For example, I'd press the button and it would take a few seconds before it would take the picture and some times I would think it didn't take the picture so I'd move and then it would suddenly release. And, it's not the shutter speed... I have it at 1/160.
I think you're right that this isn't actually a focusing problem. It could simply be that the camera is waiting for the flash to charge, or perhaps you have "Red-eye reduction" enabled, which delays the shot while the flash fires weakly to get rid of that nasty red eye effect
Try using the green auto mode to elliminate user error to see if it focuses as fast as it should. I suspect the more advanced D7000 af system is not set correctly. If you setting up the D7000 the same as the D5000, that may be the source of the problem since their af modules are different. If it is dark enough to need flash and using a slow lens you will probably need to set AF Assist Light to " on" and use Af-S. Stan St Petersburg Russia
Thank you, my first thought was the settings, like you said, the modules and settings are very different! As I mentioned in my above reply I was getting the same result in auto as manual. I think I do have the AF Assist Light on (that's the little light that comes when you first press the button) and I have it on AF-S, I also tried AF-C.