If Chapter 1 was about listening to what the histogram was trying to tell me, this one is about listening to my fingers. For a long time I tried to shoot birds the “normal” way: half‑press the front shutter to focus, then press all the way to take the shot. It worked fine right up until a perched bird decided to launch. In that split second, I’d find myself half‑pressing, lifting, pressing again, trying to switch AF modes, and basically tying my fingers in knots while the bird exited stage left.

From Popi’s collection of the most impactful photo tips: Back Button Focus was born, for me, out of that frustration. I didn’t discover it because I’m clever; I discovered it because I kept missing good take‑offs. Once I moved focus to the back of the camera and left my D850 parked in AF‑C, the whole perched‑then‑flying sequence suddenly flowed like butter. My thumb handled the focusing, my index finger just recorded what happened, and the birds finally stopped outrunning my hands.​

Photo Tips from Popi’s Pics

Essential Photo Tips for Bird Photographers

Chapter 2: Back Button Focus – When the Perch Turns into a Launch

photo tips: Switching from still to motion with one thumb, not a menu dive

The problem: when birds don’t wait for menus

On one of my early birding expeditions I ran into more than one issue I wasn’t prepared for. bird perched, you’re carefully half‑pressing the shutter in AF‑S, waiting for that perfect still frame. The bird suddenly launches; you need AF‑C, but you’re still in AF‑S and your fingers are juggling half‑press, mode switches, and composition. By the time you switch focus modes, the bird is gone or out of focus.

The real problem isn’t the camera; it’s tying focus and shutter to the same button.

What Back Button Focus actually does

BBF simply moves AF activation from the shutter button to a rear button (AF‑ON on the D850, or AE‑L/AF‑L on other bodies). The shutter button now only takes the shot; it no longer starts or changes focus. You hold the back button to continuously focus in AF‑C, or tap it once to lock focus for something that’s still.

There’s no “secret focusing mode” unlocked by BBF; the power is that you control when AF runs, independently of firing the shutter.

The magic combo: AF‑C all the time

With BBF, you can set the camera to AF‑C and leave it there, because you decide with your thumb whether focus is continuous or not. For the perched bird: tap or briefly press the back button to focus, then release; focus stays where you left it while you recompose and shoot. If the bird takes off: keep the back button held down, and the camera tracks the bird in AF‑C while your index finger freely hammers the shutter. AF‑S and AF‑C, rolled into one behavior: how long your thumb is on the back button.

---

How it would go in real time:

Perched → launch: how it flows “like butter”

1. Perched setup
   • Camera in AF‑C, BBF enabled.
   • You point at the bird on the branch/pole.
   • Thumb press: camera locks focus on the bird; release when you’re happy.
   • Recompose slightly if needed and take still shots with the shutter button; focus doesn’t jump as long as you don’t touch the back button.
2. Anticipating the launch
   • Keep composition a bit loose to leave room where the bird is likely to fly.
   • Thumb back on the AF‑ON button, ready to track.
3. The launch
   • The bird jumps; you keep the AF‑ON button held down.
   • AF‑C keeps updating focus on the moving bird.
   • Your index finger is free to shoot a burst without ever worrying about half‑pressing or refocusing with the shutter.
4. Result
   • No frantic AF‑S ↔ AF‑C switching.
   • No accidental refocus on the background when you twitch the shutter.
   • The whole move becomes: “thumb tracks, index finger records.”

---

Time‑saving benefits and fewer missed shots

No more mode‑switch panic: you don’t need to change AF‑S/AF‑C when behavior changes; AF‑C stays set, and your thumb gesture decides how it behaves.

• Faster reaction to take‑offs: when a perched bird lifts, you’re already in continuous AF—there’s no menu dive or button hunt.
• More stable recomposing: focus‑and‑recompose becomes reliable again, because the shutter no longer tries to refocus when you press it.
• Cleaner mental load: you can think about timing, light, and composition instead of “which AF mode am I in right now?”

---

Practical D850 setup (summary for readers)

• Set autofocus to AF‑C as your default.
• In Custom Settings:
  • Assign AF‑ON (or another rear button) to “AF‑ON” (start AF).
  • Disable AF activation from the shutter button, so it only takes the picture.
  • Note: you can also use two rear buttons for two different AF behaviors (e.g., single‑point vs group) as some wildlife shooters do.

Field exercise: BBF on a perch‑and‑launch session

Are you now feeling bold and resourceful? Here’s a simple exercise to do:

• Find a cooperative subject (common birds on posts, poles, or railings).
• Set camera to AF‑C, BBF enabled, continuous high drive.
• Practice the sequence:
  • Thumb focus on the perch, release, take a few still frames.
  • As soon as the bird twitches like it might launch, thumb back on AF‑ON and keep it held.
  • Track and shoot a burst through the take‑off and first few wingbeats.
• Review the files and compare:
  • Before BBF (if they have older images) vs after BBF.
  • How many frames are in focus through the launch.

---

Coming Next: Those tricky AF areas and other photography “alphabet soup”

BBF is the way you drive autofocus, but the AF area modes (single point, dynamic, group, auto) are the “tires and steering” that define how it behaves. The next chapter will cover “why use the various shooting modes” and how you pair them with BBF for birds that zig‑zag, dive, or come head‑on.

---