Focusing problem

[KenRC51]

Exposure Time = 1/50"
F Number = F4
Exposure Program = Aperture priority
ISO Speed Ratings = 200
Exif Version = Version 2.21
Date Time Original = 2010-04-02 17:29:26
Date Time Digitized = 2010-04-02 17:29:26
Shutter Speed Value = 5.64 TV
Aperture Value = 4 AV
Exposure Bias Value = ±0EV
Max Aperture Value = F2.83
Metering Mode = Pattern
Light Source = unknown
Flash = Off
Focal Length = 56mm
Subsec Time =
Subsec Time Original =
Subsec Time Digitized =
Color Space = Uncalibrated
Exif Image Width = 2848
Exif Image Height = 4288
Sensing Method = One-chip color area sensor
File Source = DSC
Scene Type = A directly photographed image
CFA Pattern = [G,B],
[R,G]
Custom Rendered = Normal process
Exposure Mode = Auto exposure
White Balance = Auto white balance
Digital Zoom Ratio = 1x
Focal Length In 35mm Film = 84mm



Some times I have trouble focusing when I'm taking a portrait close up when I have 2 subject, one close to the front and one a little bit behind the other.

I shoot in Dynamic focus and select the middle which is above the dog's head and right below the button on the polo. The picture of the dog's head and my friend's face are not focused with the dog's head a little more focus then my friend's head. (this shot was not posted)

Then the second shot which is the one I posted. It was shoot in auto area focus and every time it would focus the point either on the dog's face or my friend's face light up but not both at the same time.

I do know if I zoom out or step further back the auto focus will select both faces.

Help me out guy, Thanks

[Benji]

Read up on "depth of field." With a mid telephoto lens like you used here and with an aperture of f/4.0 there simply is not sufficient DOF to get both in focus.

Benji

[pkd14u]

Love the dog

To expand on the previous comment a little, you need a smaller aperture (larger f number) to achieve more depth of field. I would try f/11 and see how that works. You might also try to pose your subjects a little closer to each other. In other words, have them closer to the same distance from you.

[KenRC51]

I tried using a smaller aperture before and it still not as clear because the auto focus is on selected on either one of the subject.

Yeah, I know that having bother my subject a little more closer will get them to focus because they are within once focus point or range. My goal is to have them this far apart for this shot. I used auto focus on dynamic is thus the right auto focus to use? or should I use some thing else?

[Swisstony10]

There are several things which will help here, I think.

Firstly, as others have already suggested - you totally need to use a smaller aperture. If you're trying to take any kind of portrait with more than one main subject (like someone standing right behind someone, or the man and the dog shown in the picture you posted), F4 isn't going to give you anywhere near the depth of field you need. Definitely pose them closer together, and definitely stop down to something like F11 - try that as a starting point and see how things work, depending on how far away from them you are, and what focal length you're using, the depth of field will be slightly different, so experiment and sooner or later you'll get the hang of where you need all three variables to be.

The other thing is the focus setting you're using. I'm not overly familiar with the D90 (being a Canon boy), but for portraits you'll probably get better results using the Single AF setting - this'll focus just once, when you half-press the shutter button. Point your chosen AF point at the main subject's eyes (the eyes are almost always the most important bit of a portrait), focus on them, and then recompose the shot while you hold the button halfway down, and then take the shot...

EDIT - I just fired your original photo's settings into my depth-of-field calculator:
At 56mm focal length with an aperture of F4, assuming you were about 2 metres away from the man in the photo, your depth of field is going to be 21cm. Imagine stretching a tape measure from your camera, towards your subject - things will start being in focus at about 1.9 metres away from you, and by 2.11 metres, things will be out of focus again. With that narrow a depth of field, it doesn't matter what method your camera is using to focus the lens, you're not going to be able to get both subjects in focus.


Russ.

[kptasteve]

JUST A SIDE NOTE IF YOU HAVE AN Itouch or IPhone. There are several very inexpensive DoF calculator applications out there and they are inexpensive and fairly easy to work. I downloaded a couple and learned something just from putting in different scenarios.

[Swisstony10]

And if you have an Android phone, you can download the free one that I used for the above post.

Russ.

[KenRC51]

The app is called the depth-of-field calculator? I have G1.

[Mike367]

I got this online depth of field calculator from another post on DPS.

Online Depth of Field Calculator

[irishmuth]

KenRC51,

This may or may not be accurate, but based on your description of trying to get both the person and the dog as focus points it seems like you might be confused about how focusing works. Your camera doesn't simultaneously focus on two different distances, it simply uses settings with a small enough aperture to give you a DOF that is large enough for both subjects to be in focus. So as long as you have a small enough aperture (large F number), you should be able to focus on either the person or the dog and have both crisply in focus.

Sorry if I was wrong about that assumption, I just wasn't sure if that was clear previously. Also, the experts can correct me if I mis-stated anything.