Focus Point Confusion

I get the following question rather  lot – so when another reader asked a few days ago, I thought “let’s answer for everyone”.

When shooting, I usually use the center focus point (Canon 40D) to select what I want to focus on, press halfway and then recompose. I have recently gone through some pictures I have taken with Aperture 3, and have clicked “show focus points” and it shows that my focus point was off. It appears as though my camera did not lock the focus. I have done some research on different forums to find out what the problem could be, and some people discussed the modes “AI Servo, AI Focus, One Shot”… Should this affect the focus lock? Would I be better off changing which of the 9 focus points I wish to use for each shot rather than locking and recomposing? (I would rather not since it’s more time consuming!)

A-ha.

You are fine. You are using “one shot”, or you would not see a focus point displayed. You see, the “display focus point” function is only useful if you do not recompose, since the computer doesn’t know you recomposed. So the computer shows which point you used, but not where it was when you shot.

I.e. There’s no problems. The image is sharp where you wanted, right?

Your other question: yes, although the centre point is more sensitive, and is sensitive to both vertical and horizontal lines, it is usually more accurate to move the focus point. You can make this easier on many cameras by custom functions. But unless you are shooting with very narrow depth of field, you can usually get away with using the centre point and recomposing.

 

Sharpness strategies

Today, I helped a student get to grips with shooting with a long lens.

So….was it really all that long? 70-200mm. And 200mm is not actually long when you are shooting small birds, some 10m away:

This was shot at 1600 ISO – it was a dull cloudy day and with birds you want high speed, which means high ISO even when you have a good lens opened up to f/2.8.

So the lens is short. So we have to crop. And when you crop, you see the limitations (click to see this part of the image at full size):

So.. what are some strategies you can use to get sharp pictures?

First, do not shoot through obstructions. Through a clean window pane, and with a filter on the lens, we got this (a small crop out of the image):

Without the filter and window, this becomes:

Better!

Other strategies:

    1. Use a good quality lens. Lenses are not what you should be saving on!
    2. Shoot at a fast enough shutter speed. “1 / lens length” or much better. I prefer to do this by using aperture mode at aperture wide (or nearly wide) open.
    3. Now set the ISO high enough to get a good shutter speed.
    4. Use VR/IS stabilization.
    5. Consider using a monopod (or even a tripod): one with a quick release.
    6. Focus on the background, then focus on the bird, then shoot.
    7. Use One Shot/AF-S focus, unless the subject moves. In that case use AI Servo/AF-C.
    8. Focus on contrasty bits!
    9. Use one focus spot, and avoid mis-focusing.
    10. Light well, if you can – meaning “light bright and expose to the right”. My dictum: “Bright pixels are sharp pixels”.
    11. Take multiple images and use what works. Your lens will mis-focus occasionally.

      Also, consider stopping down the aperture a bit when you have to. Like when the bird is inside a tree… f/2.8 gives you this:

      While f/4 gives you this:

      That depth of field is much better.

      And one more, where a bird is “bright pixels”:

      Concluding, there is not one way to get sharp pictures. The best technique is to try to stack the odds in your favour by using as many of the techniques described above.

      Focus!

      The other day I said “focus using one focus point”. A reader asked why. So let me explain why I said that.

      On a modern SLR camera you have many focus points: 9, 11, 22, or even 40. The camera has various modes, which may include:

      1. The camera chooses from all available points.
      2. The camera chooses from a smaller area of available points.
      3. You choose a point, but the camera will look immediately next to that point if it cannot find focus.
      4. You choose a focus point, period.
      5. You choose a very small focus point.

      Method 1 is the “snapshot” mode. Methods 2, 3 and 5 may only be available on high end or very modern cameras (2 and 5 are only available on my 7D, for example). I like 3, but it too is for high-end cameras only. So usually the choice is “1 or 4?”

      In method 1, the camera chooses one or more focus point; in other words, it decides where to focus.

      What does it base its choice on?

      A lot of people think “on the subject”. No, it does not have a brain, It does not know what the subject is. The camera basically bases its choice on “I’ll focus on whatever is closest”.

      And that, as in the image below, is not always what you want. In this image I wanted the wall to be sharp – so I aimed the single focus spot between my fingers.

      Which is why you choose method 4: YOU choose a focus point, and aim that at the subject where it should be sharpest.

      There are a few things to remember:

      • You need to allow enough distance.
      • The subject needs to be well lit.
      • The subject needs to be contrasty (focusing on a blank white wall is impossible).
      • You can recompose after focusing, as long as you keep your finger half way on the shutter.
      • On high end cameras, exposure is also biased to the focus point, making it even more important to focus accurately.

      Photographers who let the camera decide where to focus are playing roulette – Russian roulette. after all, in a portrait, do I want the closest object (the nose) to be sharp, or the eyes?

      So take charge and usually, use one focus point. Focus, wait, recompose if needed, and shoot. Presto – sharp where you want it to be.

      Why is my picture blurry?

      Why is my picture all blurry?

      I hear this all the time from both experienced and new photographers.

      Well, here’s why.

      Focus:

      • You have not focused properly. Solution: select ONE focus point; focus; hold it; and only then shoot.
      • You are using a shallow depth of field. At f/1.4, it is hard to focus.

      Subject:

      • Your subject is moving fast. Solution: pan with the subject or increase ISO, open aperture, or shoot the subject at the apex of its jump, say.

      Shutter speed:

      • You are using a slow shutter speed (slower than twice the lens length, say, so on a 100mm lens you are using a shutter speed slower than 1/200th second). Solution: open the aperture or increase the ISO).
      • You are using a long lens (say a 300mm lens). On that lens, fast enough shutter speeds are hard to obtain). Solution: Zoom out, increase ISO, open the aperture, or use a tripod.
      • You are not using a tripod when you ought to. Solution? use a tripod!
      • You are using a slow lens. An f/3.5-5.6 consumer lens will never do as well as an f/2.8 pro lens. Solution: need I say?
      • You are using a small aperture, like f/8, when you should be using f/2.8. Solution: open your aperture.

      Miscellaneous technique:

      • Your subject is in the dark – where it is muddy and blurry. Solution: Light your subject well.
      • You are not using flash when you should be. Solution: need I say?
      • You are  not using IS/VR. These are great features: stabilized lenses are superb and give you several stops. Solution: get an IS/VR lens.

      Equipment:

      • Your camera is faulty – this is very unlikely, but have it checked out.
      • Your lens is faulty – this is also rather very unlikely, but have it checked out.

      Clear? (Pun intended). Try all these and you will see your images improve amazingly.  Yes, I know, there are a lot of them. Yes, it’s complicated. But yes… you will take brilliant images once you get all of these right.

      Remember these tips:

      • Bright pixels are sharp pixels (that is Willem’s Dictum);
      • Flashed pixels are sharp pixels;
      • VR/IS works;
      • Use one focus spot;
      • Hold the camera right;
      • A tripod is a good thing.

      Have fun – a crisp, razor sharp picture really is a joy.

      Manual focus? Six reasons.

      Should you ever focus manually? When?

      Well, yes. Indeed there are circumstances where manual focus (setting lens or camera switch to manual focus, and turning the focus ring yourself) is the way to go.

      And here’s a few of those circumstances. I can think of six right away:

      1. Macro. When shooting macro, for instance when shooting flowers, bugs, food or jewelry, use live view and zoom in electronically if you can, then use manual focus.
      2. You are using a Nikon D40/60/3000/5000 and a fast 50mm lens. Those lenses do not autofocus on those low-end Nikon cameras, so you have to do it by hand.
      3. It is night. Your camera cannot focus well in the dark.
      4. When shooting through glass, like on an airplane.
      5. The subject has low contrast. Ditto – you may have to do it by hand.
      6. When the subject is unpredictable in time but not in space – like fireworks. Or sports, when you know where the action will be. Pre-focus there manually!

      Tip: Do not confuse manual focus with “using one focus point”. When using autofocus, you should always (or virtually always) use one focus point. When the camera chooses it will choose what you do not want to see sharp.

      Homework: go take ten pictures right now where you focus manually. You;ll see how easy it is, and how consistent once you get it right.