Focus Tip: AF-C/AI-Servo and back button focus

I am often asked “can I not leave my camera on AI-Servo (AF-C if you are a Nikon etc)?

The answer is: not a great idea normally. Because you cannot recompose. The moment you try that, taking your focus spot(s) away from your subject, the camera focuses on whatever is behind the subject!

But there is a trick, and I used it today to photograph these amazing insects:

Namely this:

  1. Set your autofocus mode to AI Servo/AF-C.
  2. Select “back button focus” in your camera’s menu (i.e. focus when you press a button on the back of the camera, not whenever you half-press the shutter button).

Now you focus as follows:

  1. Follow the insect, or hockey player, or whatever you are shooting.
  2. While doing this, keep the back button focus pressed, so your camera adjusts to follow the subject’s distance.
  3. But when the butterfly sits and you want to recompose, let go of the back buttoin focus. You can now move the camera to recompose, yet when you shoot, the camera will not adjust its focus.

Done and done!

A quick note about that amazing insect. Nature knows what many beginning photographers do not: you need a catch light in the eye to make it look real and alive. The butterfly’s owl eye has that catch light (the white circle part ion the “pupil”)! Amazing, eh? So learn from nature and always include a catchlight in your portraits.

 

Back button focus: Why and how.

Some photographers (like me, usually) prefer to use “back button focus”. That means that instead of focusing by pressing the shutter button half way down, they focus by pressing a button on the back of the camera. Usually the “AF-ON” or “*” (asterisk) button top right on a Canon camera like the one below. The shutter button now only operates the light meter (in manual mode) or sets the exposure (in automatic and semi-automatic modes.)

On most Nikon cameras, you can use the AE-L/AF-L button on the back to operate focus.

Why would you want to do this?

You might not, or you might. If you prefer this, it is probably for some of the following reasons:

One is that it is easier to separate the process of determining and setting exposure from the process of determining and setting the correct focus distance. These are separate processes that have nothing to do with one another: why combine them into one button? You may well want to focus on the bride’s eyes, while taking an exposure reading off Uncle Fred’s grey suit. This way I set exposure and ignore focus. When I am done and exposure is good, then I go focus where the image should be sharp, and forget exposure (or vice versa). And the two areas do not need to be the same. And usually they are not the same. Unless, of course, your bride has 18% grey eyes.

Also, it is easier to “set and forget” one or both. If, for instance, your distance to the subject does not change, why should you have to re-focus for every shot? There are plenty of situations where this is the case. Like portrait headshots. Focus once, then concentrate on expression and pose, not on focus. By using a separate button you make it possible to do this: focus once, and then forget it until you or the subject changes position.

The third advantage of focusing like this is that it is now easier to make manual adjustments. I focus using autofocus, but sometimes I want to adjust manually. No problem. I can do that, If my camera is set up for back button focus. Beep focus, then overrule that with manual focus.

How?

How do you set it? That depends on the camera. A few examples/notes:

  • On most Canon cameras it’s a Custom Functions (C.Fn) entry or two. For instance, on the Rebel T3i you use C.Fn 9 (option 1 or 3).
  • On the 60D, use C.Fn IV-1 (option 1, 2, 3, or 4)
  • On my 5D Mark 3 it is done in the Custom Controls section of the Quick (“Q”) Menu: set Shutter Button Half-Press to “Metering Start”, and set AF ON to “Metering and AF Start”. I usually also set the AEL button (the asterisk) to “Metering and AF Start”. That way I can use either the asterisk or the AF-ON button. Less chance I miss it!
  • Exactly the same applies to the Canon 7D.
  • On Nikon cameras, set the AF-L/AE-L button to “AF ON”. To do this, go to the pencil menu, find section “controls”, and use “Assign AE-L/AF-L button.”  Within this menu, choose “AF-On.”

Q: Michael, didn’t you say “back focus” was to be avoided?

A: Yes. But this is “back button focus”. A very different thing altogether. “Back focus” means the focus is inaccurate. “Back button focus” means that we are using a button on the back of the camera to start the focus process.

Q: So should I start using back button focus?

A: No, unless you understand all this, know your camera, and are happy to benefit from the advantages I outlines—and only if those are important to you. It’s no big deal either way; I go back and forth between using it and not using it. But now at least you know what it is all about.

 

Live View—a tip

Live View (seeing the photo on the back of the camera instead of through the viewfinder) is not generally recommended. Use the viewfinder!

Except in a few special circumstances.

Namely, you would use Live View when you need accurate manual focusing. This is often the case when shooting macro, or product, or night pictures, when the camera’s autofocus either will not work well, or is not accurate enough.

On many cameras, like on my Canon bodies, you can:

  1. Set focus to “manual” (slide on the lens goes to “M”);
  2. Put the camera on a tripod;
  3. Activate Live View;
  4. Zoom in on the preview (press the “+” loupe symbol, or just the loupe symbol on many Nikon bodies). Repeatedly: on the Canons, when you press it twice, the preview shows (10x” (i.e. 10x magnification);
  5. Now focus accurately by hand;
  6. Now turn off live view.

You are now ready to shoot. Ensure that your subject and camera do not move, and that you do not zoom in or out after focusing (most lenses will lose focus if you do), and especially, that you do not accidentally move the focus ring.

I am writing this as I prefer to do some night sky shots in the next few days, provided I can find a clear sky without too much light pollution.

By the way, my favourite lens for night sky shots is my 35mm f/1.4, which offers pretty much the best combination of:

  • Large real aperture diameter (means more light gathering) and
  • Wider angle (means longer times are possible without creating star trails. To understand why, imagine a telescope: the longer it is, the more the stars will move).

14 seconds at 1600 ISO at f/1.4 should do it. And at that aperture, accurate focusing is essential—which brings us back to where we started: manual focus using Live View.

 

Back to basics

One thing I notice is that often, even working photographers get focus wrong. So let me go back to basics with you today. Focus basics.

There are two focus “settings”: where to focus and how to focus. Today, where to focus.

In the basic “auto” modes, you let the camera choose. You see all focus areas (all three, or all 9, or all 11, or all 42 – depends on your camera) and when you press the shutter halfway, the camera indicates which ones it uses.

These are the ones that have a close object. So you would get this:

But is that clever? Surely you should choose? Perhaps you want this, instead?

That can only be done if you:

  1. Select one focus point (read your camera manual if you need help doing that)
  2. Aim that focus point at the subject you want to have sharp
  3. Press half way down (you will hear a beep, if you haven’t disabled the beep)
  4. While holding the button half way down, recompose, if you like
  5. Press the shutter all the way down to take the image.

This is how you shoot most of the time. Letting the camera choose where to focus is not a great idea. It does not have a brain, and even if it did, it wouldn’t be your brain.  And no, “more focus points” does not mean “greater depth of field, i.e. more focus”! It merely means “camera gets to choose”.

So go set your camera to one focus point pronto!

 

Challenging Shots

Some shots can be a little tricky. Like this one, from Sunday’s shoot:

Tricky why? Because the model is jumping, making it hard to focus.

The solution? You could try AF-C/AI-Servo, i.e. continuous focus. But often in these cases a better solution is this (and that is what I did): pre-focus, then hold that focus while he jumps. So I had the model stand where he would be when I take the shot; then focused there and held that focus while he moved back and jumped; then I shot when he was once again in the same place.

Why is he not blurry? Because he is substantially lit by the flash, which fires faster than 1/1000th second.

Another, different challenge was presented by this shot:

Why? Because the original plan was to light the aquarium in part from behind. But I was shooting TTL, and guess what? I found out on Sunday that the light-driven TTL does not work through an aquarium. Fancy that. You learn something new every day, even when you have been doing it forever.

The solution was to light it from the sides instead, after removing the aquarium side doors. Sometimes you just have to change your plans a little bit!

Enjoy your speedlighting, everyone. I am off to sleep – finally, at 3AM.

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.