STILL struggling with focus. ;(

[AMOMENT]

I have a Nikon D3100 and usually shoot children/people with my 50 mm f/1.8 lens from as close as 2 or 3 feet away to as far as 10 feet. (usually no further) I always auto focus but sometimes select one of my 11 auto focus points which are arranged in a grid with five points horizontally in the middle and three on top and three bottom.

When I select any other focal point from the grid other than the central point, only one point is highlighted red at a time through my viewfinder.(the one I selected) However, when I select the central one, usually a point above it or below it is also highlighted. My interpretation of this is that maybe the central point is more dynamic? Cross points right? The photos which have been out of focus, which I have not posted, have been the ones where I have selected either the far left or right points, top, or bottom. I do so because I then position that point on either the left or right eye of my subject. If I were to select my central most point, then the point would end up (most likely because of my composition) being on their nose. I want it focused on an eye right? I can't select more than one auto focus point. When I use af-a and auto focus area point in my manual priority with my 50mm, the photo is almost always completely out of focus. I'm obviousely doing something wrong.


What would you recommend? I know that taking the photo from 2 feet away to 10 makes a huge difference. However, for now, I am trying to master just getting my subject's face in perfect focus rather than being creative and say, getting the person's feet to be in focus. I can select af-a, af-s, af-c and then either dynamic, or single, or auto AF for area mode? As I mentioned, I have 11 auto focus points.

Thanks....

 

[AMOMENT]

Hypothetical scenerio: If my subject is three feet away and I most likely have 10 seconds AT MOST to capture him/her and I want him to be in the center of the photo, what would you do? I know DOF plays into this as well in that depending upon how shallow or great my DOF is, will determine how much/what part of my photo is in focus. I tend not to shoot wide open; 1.8 but rather 2.8 or 3.6 around. (at least for someone anywhere from 3-5 feet away)

 

[2WheelPhoto]

At 3 feet away 3.6 is still a large aperture

 

[AMOMENT]

okay, so if I shot at 5.6 would that be better? What about the settings?

 

[2WheelPhoto]

Well, check out how tight depth of field is on this chart: Depth of Field Table

 

[cgipson1]

Hypothetical scenerio: If my subject is three feet away and I most likely have 10 seconds AT MOST to capture him/her and I want him to be in the center of the photo, what would you do? I know DOF plays into this as well in that depending upon how shallow or great my DOF is, will determine how much/what part of my photo is in focus. I tend not to shoot wide open; 1.8 but rather 2.8 or 3.6 around. (at least for someone anywhere from 3-5 feet away)

with a 50mm lens... at 3ft to your subject... at F3.6.... your depth of field looks like this

Depth of field

Near limit 2.93 ft

Far limit 3.07 ft

Total 0.14 ft or about 1.5 inches DOF

Does this maybe give you a clue to why you are having a hard time with focus?

Even F8 at 3ft only gives you about 3 inches of DOF

http://dofmaster.com/dofjs.html

 

[MTVision]

okay, so if I shot at 5.6 would that be better? What about the settings?

You kind of have to figure out what works for you.
The only time more than one focal point lights up is if my camera is set to auto-area AF. With my camera set to af-area mode single point AF only the focal point I choose lights up regardless of whether I use the center point or not. AF-A doesn't let me choose my focal point at all.
AF-A switches between af-s and af-c
Af-s is for a single point focus
Af-c is for continuous so if your subject is moving it will keep refocusing to keep the subject in focus.

"Still photos are best taken using the one-shot autofocus mode, which ensures that a focus lock has been achieved before the exposure begins. The usual focus point requirements of contrast and strong lighting still apply, although one needs to ensure there is very little subject motion.

For portraits, the eye is the best focus point—both because this is a standard and because it has good contrast. Although the central autofocus sensor is usually most sensitive, the most accurate focusing is achieved using the off-center focus points for off-center subjects. If one were to instead use the central AF point to achieve a focus lock (prior to recomposing for an off-center subject), the focus distance will always be behind the actual subject distance—and this error increases for closer subjects. Accurate focus is especially important for portraits because these typically have a shallow depth of field."
Www.cambridgeincolour.com

Look up online for some focus exercises. My settings may work for me but they won't necessarily work for you. I know you don't like still life photos but that's goin to be the best way IMO to practice focusing. Practicing on moving children will be more difficult. Experiment with all the settings and see what works best for you.

 

[KmH]

Quit using AF-A. For people shots use AF-S.

Re-read pages 55 through 63 of your D3100 user's manual, paylng close attention to details about photographing people, like focus/recompose.

Consider moving the auto focus function from the shutter release button to the AE-L/AF-L button (AF-On) on the back of the camera (see page 146 of the D3100 user's manual)

 

[gsgary]

I thought that lens could not auto focus on that body, Canon user so not 100% sure

 

[KenC]

Why not focus manually? In less time it takes to focus/recompose your fingers on the lens focus ring could snap the eyes into focus.

 

[myko5]

I just bought this lens and am also having problems trying to nail focus. Thanks for posting up this thread, it has some very helpful information.

I thought that lens could not auto focus on that body, Canon user so not 100% sure

If it is the AF-S version it will.

 

[mc1979]

I have a stupid question, I always shoot AF-S, but I manually choose my focus points. Am I doing that wrong?

 

[KmH]

No, but your D3000's center focus point is more accurate than the other 10 focus points. Understanding Camera Autofocus

There are regular (single axis) focus points, and then there are cross-point (2 axis ) focus points.

So if your subject is not moving it's best to use the middle focus point wherever in the scene you want the focal point, lock focus, and then recompose the framing for the composition you want.

Using focus properly is so very basic to doing photography.

But understanding focus takes some study, because there are various focus modes (and various focus area modes) plus depth-of-field.

Depth-of-field is so very important to focus, but it is affected by lens focal length, lens aperture, focus point distance from the camera, and focus point distance to the background.

While photography is nowhere close to being rocket science, there are many technical aspects that have to be understood to do photography well, consistantly.