Well... I'll come clean... none of my current (or previous) Canon bodies does this...
Here goes. Especially in challenging lighting conditions, the AF on my D700 "micro-hunts" for the "perfect" focus. It takes maybe twice the time my dusty 5D does to lock, by shifting around the perfect focus 3-4 times (sometimes more). It basically acts like a servo system (which it is) with a big (or improperly tuned out) inertia mismatch, by overshooting its intended position, coming back, overshooting again (by a smaller margin) and so on until it reaches the proper position. While all this back-and-forth going is actually pretty quick, it still taking longer than my 5D in similar conditions. Granted, the D700 will actually try and finally acquire focus in situation where the 5D simply will not work at all.
The actually really puzzling bit comes however in excellent light with plenty of edges for good focus target where sometimes the D700 will still go twice while the 5D will simply send the focus where it needs to be and stay there (100 % of the time). It's almost like D700's AF "nervousness" is working against it...
Both cameras are set to single focus (center) point and single shot AF settings (AF-S on the Nikon) 28-70 f2.8L on the Canon, 24-70 f2.8 on the Nikon (awesome lens btw)
Does anyone else experience this sort of behavior? Is this normal for Nikon? (my even older D70 sort-of does it as well at times).
Hrm, I've never experienced that on either a D300 or D700.
It's possible your center point is actually picking up a focus point near the box and adjusting there.
The back-and-forth thing sounds like Pentax's focusing system, not really nikons.
Have you done some focus testing yet to see if the lens is front or back focusing? Maybe that's causing the hesitation.
My D300 does this in low light with the 50f1.8d and 85f1.8d exactly why I got rid of both of them seeing as the 18-200 VR doesn't do this. It sounds to me like you need to send that D700 in because it might be faulty...
Poss wrote:
Well... I'll come clean... none of my current (or previous) Canon bodies does this...
Well THAT's hard to believe ! Every Canon camera I've had does that in AI Servo, with the pro models doing it less but still doing it. In One Shot mode they won't hunt but may also get the focus wrong because they work on a system of trust - telling the lens where to focus and expecting the lens to obey. Depending on the release mode some cameras indicate that they have achieved focus when in fact they have not - there's no great delay but it's cheating. The 5D was known for this (reported a number of times on the canon forum over the years).
If you use a Nikkor AF-S lens then it should not be happening unless the distance to the subject is changing (more likely when close-up). However, make sure you have the latest D700 firmware as it helped to settle the AF down and improved low-light performance. There's also the effect of settings such as focus release vs shutter release priority.
Finally, the Nikon AF system works at any effective aperture but gets progressively worse as it runs out of light. This is different from the canon system that just stops beyond a certain effective aperture regardless of available light.
i've read something about this a long time ago. Canon's af system is a closed loop system while nikon uses an open loop system... Or something like that. There are quite a few technical experts here on the board i hop they chime in to explain, because i'm unable to do so.
FWIW I wouldnt listento anyone who hasnt had this problem. You'll be getting alot of people that claim its you because theirs doesn't exhibit the same symptom.
having said that, I had the exact same problem. My AF would micro adjust, back, front back, front closer and closer til it locked. which it eventaully did but took a long time, from 1-4 seconds, it only did it in low or really contrasty focus zones. AF-S or AF-C and many different lenses all had the same result. Then nikon released a firmware update, and the problem for me anyway, dissapeared. Ever since its been the fastest and most accurate body Ive used, better than D1/D2 but i never used a D3.
I hope it'll help you.
Hey Alan,
My 5D is even more frustrating in Ai Servo. Its focus changes sometimes unpredictably resulting sometimes in perfectly focused backgrounds with perfect bokeh on my subjects . I stopped using this mode after the first few shots.
The 5D is in single shot AF mode pretty quick (even quicker in dim lights than the older 1D sries I've tried and used over the last years) but not particularly accurate (not garbage either). Usually half pressing again will result into a small micro adjustment and better accuracy. The 5D focus usually goes where is told and stays there, which lacks ultimate precision but is quite fast. Its main falling is AF sensitivity. The tech specs will put this 1 stop worse than D700 but in my experience it is actually worse (actually to be truthful D700 is probably better than published specs rather than 5D being worse... my 2 canadian cents)
BTW, Canon's AF modus operandi is not cheating, merely a design choice in focus feedback (and how to deal with it) that may work well for some shooting styles. Certainly works for mine...
Anyway what I'm after in this thread is user experience with this issue (it seems I'm not alone), workarounds and all (maybe a trip to Nikon, which I'd rather avoid for the time being).
. I stopped using this mode after the first few shots.