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Autofocus off with D90 35mm f/1.8G

d90 autofocus

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4 replies to this topic

#1
whiteShadow

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Hello,

 

I have been trying to make some shoots with a friend recently with my d90 (35mm f/1.8G) and I noticed that I have much sharper images when using the manual focus instead of the autofocus. 

My friend is always slightly blurred when using the autofocus (even with the single point focus). It's not so much visible if you look at the image globally, but if you start zooming, you can see details (like beard) is blurry.

 

The problem is that manual focus is very sensitive, and then takes time to be perfect, but sometimes I need to be fast, or if I or he moves, then I have to restart all over again.

 

As mentionned, I tried with single point autofocus, but even putting my subject at the center while focus, the focus is made on the background, as you can see on the images. On the uploaded images, in the AF, I put the leaves (my subject) at the center, and I focused on it, but it failed. I tried with bigger subject (like a person) and it still fails most of the time to focus properly. Am I using the single point focus badly?

 

What could I do to have a very accurate autofocus?

 

Thank you.

 

Attached Thumbnails

  • AF.jpg
  • MF.jpg


#2
TBonz

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The two images you posted look correctly focused to me if you are using the center point...Perhaps it would help if you provided your focus settings and the exposure settings.



#3
Jerry_

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I think that in the first picture you just was at the border (and maybe next to) of the leaves having the camera therefore focussing on the background.

If you would post two diagonal lines on a print of this first picture, where would they cross. How close would this be to the leaves? (Provided this was taken with a single central focus point)

Alternately, if you have CaptureNXD it allows you to show which focuspoint was used for that capture. (Right click on the mouse and in the context specific menu choose 'Show focus point')

#4
whiteShadow

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Yes, on the pictures above, it seems the focus has been made on the background for one of them (though I'm sure the center was on the leaf). The problem I usually face is that AF is not accurate enough. I have a shallow depth, and if the focus is not 100% accurate, then my subject is slightly blurred.
I will try to get some new pictures tomorrow so I can post them.



#5
Merco_61

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One thing to remember is that the focus box usually is a little smaller than the actual focus sensor. If the contrast is better somewhere else than the center of the box, that is where it will focus.  Leaves are often difficult focus targets as they are so seldom still because of the wind.

Shooting with continuous AF controlled by the AE-L/AF-L button usually gives better/more consistent results as you decouple the focusing action from the shutter button. AF-C will not stop when it finds something contrasty to lock on to, but will continue focusing as long as the button is pressed.







Also tagged with one or more of these keywords: d90, autofocus