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best autofocus mode/tricks for D7500 video?


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5 replies to this topic

#1
satz

satz

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hi all

 

I'm happy with the D7500 as a still camera, and pretty sure I can use all the various autofocus modes, points okay.  Admittedly I do all my still photography through the viewfinder, not live view.

 

When I use video I'm so confused!    Focusing never seems to work well.   Not just slowly, but most of the time it does not focus (unless I use touch focus), or keep half-pressing the photo-shutter button!

 

I'm trying to use it as a general purpose video camera when on holiday.   So i need to use settings that will work 'straight away' when I need to video something.

 

I don't know whether to use touch focus or not.  When I don't use it, the camera often does not focus at all.    I don't understand why it always focuses when I use touch focus but not when I don't use touch focus (in exactly the same test conditions)...

 

Should I use AF-F  or AF-S in video?

 

And 'wide' or 'normal' or 'tracking'?

 

please help...

thank you

 

 



#2
ScottinPollock

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Use touch focus or manual focus. The AF modes are pretty poor on this camera (and most Nikons).

#3
satz

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hi ScottinPollock,

 

I'm confused why the Touch focus actually focuses when the camera doesn't auto focus on the same subject.   I thought the touch would also use the same focusing system?

 

It's weird, apart from this focusing issue, the video image looks great!

 

S



#4
ScottinPollock

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Hi Satz...

 

The issue is the algorithms used in continuous auto focus. First, Nikon uses a rather pedestrian implementation of contrast based detection for live view focusing. So, it is slow and hunts a lot. Also, Nikon lens' focus motors are not designed for contrast detect focus systems so that further complicates the issue.

 

When you touch to focus, you are telling the camera to measure one spot and adjust focus until the highest contrast ratio is achieved there. Not too big of a task there (if you're not in a hurry), the camera will simply rock the focus back and forth until it gets it.

 

When you are using continuous focus in video, you are asking the camera to keep things in focus. But what things? How often should it check? How sensitive should it be? For these things to be properly arrived at, some pretty good tracking algorithms need to be in play here, and Nikon has simply not been heavily invested in that tech for their DSLRs.



#5
satz

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Many thanks ScottinPollock

 

For general purpose video what would you suggest in terms of using AF-F or AF-S?   

And the 'normal' or 'wide' focusing option?

 

which settings would you use?

 

cheers



#6
ScottinPollock

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I would use AF-S, and map the AE-L button to focus (back button focus). This allows you to avoid refocusing between clips via the shutter button. But if you need to pull focus while rolling, I really would suggest doing manually to avoid the pulsing you get from the autofocus.
 
As for normal vs: wide zone... it really depends on what's in the frame. Contrast detection depends on an area that has contrast. If the normal zone does not contain such an area go wide. Otherwise, the smaller area will give more accurate results as there will be less ambiguity regarding just what part of the frame will be in focus.