catalint Loc: oslo

Hi fellow hogs,

For a while I have had this challenge regarding focusing correctly. This is not a matter of "how-to", but rather "What Am I doing wrong?". Yes I've been googling, and watched this and that, but I can't get answers from that. So I hope a good eye here can see what's wrong.

Case is like this. Dont remember exactly when I did, but like 2 years ago, I started using single focus point. Also my camera is mostly on M-mode. Camera is on AF-S most of the time. Sometimes I switch to AF-C when lot's of motion. Ofte I need to move the focus point a little to the left , right, up or down, depending. Having one single object as subject, I have no problems, but I am not happy with pictures where I have like two three persons in the picture. One persons will be focused, the other one is slightly out of focus. For me it looks like single point focusing has a very small radius. Let say you have 3 persons in the frame, you point in the middle, focus and shoot. While the middle will be in focus and sharp, it gets less sharp further from the center. I know AF-S should be used with dead stationary objects, I read it somewhere. Does this mean one should switch to AF-C as soon as you have a little movement ? Like my little niece in the picture below. She is actually in movement since my sister is swinging her. but it wasn't fast.

So how do you focus, correctly for the whole frame with single AF point?

Below is a picture to show you what I mean. My sister and one of my nieces, taken yesterday. I was like 10m away from them, and took this picture at full zoom from my 24-120mm Nikon F4.5. My sister is looking good and sharp (could have been better also in my opinion), while my niece is a little blurred. From the exif data I see I should have probably raised up the shutter speed a little more, and maybe I would have had both as sharp? Or is it cause my camera was back focusing on my sister? I can't determine if this it's clearly from low shutter speed or wrong focusing system.

What settings would you fellow hogs have used in this kind of situation ? I know lot's of you also swear to single focusing point, so I hope to hear if you encountered this problem. I do not think there is something wrong with the equipment, it has to be ME. I need to improve.

(Download)

MtnMan Loc: ID

The issue is Depth of Field (DOF).

Your camera can only focus at one distance. Using single point focus means you control that point. I have found that works best.

You increase the DOF by increasing the f-stop. Get one of the free programs to see what the DOF is for the settings you are using. You will quickly see why you can't get everyone in focus at the same time unless you use a high f-stop; e.g. f16. Particularly if you using a longer lens (e.g. 100 mm or more).

What lens (and setting if zoom) did you use for the example? You'd need an f-stop to get a DOF of at least 2 feet. For example, with a DX camera at 10 feet with a 50 mm lens it requires at least f5. With a 100 mm lens, f18!

Leitz Loc: Solms

Use a small enough aperture so that everything you want in focus is within the depth of field.

Dave45109 Loc: Michigan/Wisconsin

set up a test to see where you are focusing, set up three objects 15 -20 feet away and 6 inches apart ( I use 3 bricks on a banister on my deck) and then focus and shoot on the middle one and see if that is dead on or is the back one or front one more in focus. Also shoot at different F stops to see if there is a difference.

DavidPine Loc: Fredericksburg, TX

catalint Loc: oslo

Interesting as I was on the idea of having a new look at DOF. I've started to noticed the difference when using small apertures. On this picture I used 7.1 Should I have tried even smaller ?
Thank you for suggesting to look in to the DOF. :) I needed that kick in the butt to do it, so now I will.

catalint Loc: oslo

Seems like i need to do that.
Thank you for the suggestion.

MtnMan Loc: ID

If you were at 30 ft. (10m) and 120 mm f7 is good. DOF is 5 ft. (2 m).

So in this case it was shutter speed. Something coming at you needs a shutter speed at least 1/250.

catalint Loc: oslo

Thanx MtnMan.
When I read your first reply, my thought was exactly that. I did use F7.1, and it was with the intention for sharpness. I did suspected the shutter speed was the reason in this example.

Thou, I will need to set up a little lab and get to practice this a little more. I've started to tell myself what settings I should use before taking the picture, then after the first attempt, I correct myself. So i need a little more practice where DOF is the key.

Cheers

camerapapi Loc: Miami, Fl.

You need to improve. Let me begin by saying that most AF problems are seldom due to camera's error. I have said here before that I never had a Nikon body with front or back focus.
When necessary and that usually implies moving subjects, raise the ISO speed so that the camera will give you a higher shutter speed to freeze motion. In this case your niece was moving while your sister was stationary or mostly stationary.
AF-S is great for stationary subjects but if you have moving subjects it is better to use AF-C. Depth of field falls when using larger apertures although at around f8 this shot should be in focus. I believe that a faster shutter speed in this particular case would have done a better job.
You have to review AF techniques and consider a high ISO whenever shooting moving subjects. The smaller the lens opening the higher the ISO to get a decent shutter speed to stop motion.
Finally, AF-S is not the best choice for moving subjects. Dynamic AF with AF-C would be your best option.

Leitz Loc: Solms

Here is one of several depth of field calculators:
http://www.dofmaster.com/dofjs.html

Edit: I like that one because it gives you the near and far distances, and also takes into account your particular camera/sensor, &c.

rmm0605 Loc: Atlanta GA

catalint Loc: oslo

Thanx Camerapapi,
Improving, no doubt I do need to practice more, but I've started to get the hang of it. AF-S has become my standard, and got very used to it, and got very good result. But I've started to see that AF-S is not always the best choise. I think, after this weekend, I became a little more aware the fact that I do need to take in use AF-C a little more. I have read about the differences several time, I just haven't come to putting both in practice as the situation demands. And yes. shutter speed was one of my thoughts regarding this example.

Question is :If I would have payed attention to my shutter speed, do you think I would have nailed this picture even using AF-S ?
I wish I could recreate this picture, but using AF-C, to see how it would look. I think the answer would the same since shutter speed was 200.

catalint Loc: oslo

Thank you Leitz.
I will give it a try

RWR Loc: La Mesa, CA

In my opinion, you are handicapping yourself by your choice of equipment. To quickly and easily nail focus on both subjects I would use a manual focus lens with a depth of field scale. And your subjects won't run out of patience while you're fiddling with depth of field charts, AFC, AFS, focus here, focus there ... They may even want to come back for another session! And indeed a charming session that was!