Nikon D5100 focus problem?

Rickpaes · Jan 7, 2012

Recently bought a D5100 and have the following situation.

In Auto área-Af it doesn't focus if the subject is far or the horizon. Um dynamic área or 3D it works.

Is this normal?

Thanks

MTVision · Jan 7, 2012

Auto Area AF uses color information and special face recognition algorithms to automatically focus on an individual’s face, which is extremely helpful when there’s simply no time to select a focus point, or when using Live View in hand-held mode at high or low angles.

What are you using for autofocus - af-a, af-c or af-s???

Rickpaes · Jan 7, 2012

Af-a.

Even just a few meters away it happens the same thing

MTVision · Jan 7, 2012

Rickpaes said:
Af-a.

Even just a few meters away it happens the same thing

Why not try af-s and see what happens. Right now the camera is choosing where to focus so it's going to jump to a high contrast area. Maybe if you choose what focal point to use and where to focus it - it will work better.

Rickpaes · Jan 7, 2012

With Af-s is a little better. But not To focus in the horizon or buildings far its not normal in auto area or is it?

MTVision · Jan 7, 2012

Rickpaes said:
With Af-s is a little better. But not To focus in the horizon or buildings far its not normal in auto area or is it?

I'm not really sure but it makes sense that it wouldn't do a good job. How does the camera know you are trying to focus on the horizon or buildings in the distance? It doesn't. It is just going to pick an area of high contrast and use a bunch of different focal points to try and get what it thinks is the subject in focus. Cameras aren't that smart. If you want it to do something that it won't do automatically - you are going to have to do it yourself.

Rickpaes · Jan 8, 2012

I'm taking it To the store tomorow. I concluded that somehow a sucessfull focus (in full auto) depends on the top focus point being in touch with something with contrast, even if the remaining focus points have something To focus. Very strange.

Thanks

KmH · Jan 8, 2012

Let us know what they say.

I don't think it's strange at all. I think you expect the camera to do something it is not capable of doing, because you don't know how the camera does auto focus.

Page 40 of the D5100 user's manual details just some of the common limitations auto focus has.

MLeeK · Jan 8, 2012

Are you using one or all of your focus points? if you are using multiple focus points the camera will pick the point with the most contrast to lock on to and that's where it focuses. That could be anywhere in the image and if the background/horizon has more contrast than your subject, that's where it is going to lock on. If you want to control exactly where your focus will fall you need to use one focus point and lock it where you want to have your focus fall.