Trap Focus on the Nikon D4

Trap focus comes to my D4 – Yay!!!!!!!!

What was it Nikon said – “we left it off the D4 because no one wanted it”….or words to that effect.

Well, with today’s (March 18th 2014) update version 1.10 trap focus is back – in a fashion.

What is trap focus some may ask.  Well it’s basically pre-focusing on a particular distance or spot where you expect the subject to be or to pass through.

As the subject enters the frame and gets closer to the camera it’s also getting closer to the pre-focused distance, and when it reaches the set focus distance the camera actually detects the subject/image is sharp and so takes the shot.

Basically you sit there with the shutter button fully depressed, but no shots get taken until the camera AF system deems the subject is now in focus.

It’s a technique that a lot of sports photographers find very useful, but I find it has very limited use for my wildlife & natural history work.  Having said that, it’s got me out of a bind more than once over the years, but ever since the D4 came out you’ve not been able to use it.

The failing lay in the flawed D4 focus priority – even if you told it to only trip the shutter when the image was deemed ‘in focus’ by setting CS a1 & a2 to FOCUS, it would still fire as if a1 and a2 were set to release priority.

But the new firmware update v1.10 has given trap focus back to the D4, but before you start jumping up and down and getting all excited you need to know how to set it up, and bare in mind that “as a technique” trap focus might not suit what you had in mind.

Setup for D4 Trap Focus

1. Update firmware to v1.10 – read the instructions FULLY before you attempt this, otherwise you may need another camera!
2. Go to Custom Settings a2 AF-S priority selection and set to FOCUS.
3. Go to Custom Settings a4 AF activation and set to AF-ON only – this takes to AF activation away from the shutter release button.
4. Put a wide angle lens on the camera.
5. Set the lens focus switch to M/A
6. Set the D4 focus mode selector (the lever on left side of the body front) to AF
7. Press the AF mode button and rotate the Command Dial (back one) to select AFS and NOT AFC.
8. Rotate the Sub Command Dial (front one) to select S (single) and NOT Auto.
9. Focus on your computers monitor screen using either the manual focus ring of the lens or the rear AF-ON button next to the Command Dial.
10. If you’ve pressed the latter TAKE your thumb OFF!
11. Move the camera directly away from the computer monitor screen so the image in the viewfinder goes soft.
12. Jam your finger down on the shutter release. Nothing happens (if it does then start again!).
13. Keeping that shutter button depressed and NOT touching the lens or AF button, move back towards the computers monitor screen – the shutter will fire when the monitor screen is sharp.

Got that?  Good!  Oh, and by the way, the award-winning shot you just missed – it would have been epic!

Now you’ve got a D4 that does trap focus.

Now for the trap focus caveats:

Trap Focus only works in AFS – not in AFC.

Trap Focus only works with a single AF sensor, AFS-S – so correct prediction of that one AF sensor/subject alignment to get the required ‘bits” in sharp focus and DoF is going to be difficult.

Common Kestrel Landing
©Andy Astbury/Wildlife in Pixels

Do NOT think you can pull this wildlife shot off using TRAP FOCUS.

By the time the camera has detected the sharp focus and got over the system lock time and triggered the shutter, the bird will be way closer to the camera – and sharp focus in the resulting image will be behind the tail!

This shot is done with a manual focus trap – a completely different technique, as described HERE

The subject is too small and so to close to the camera and 500mm lens for trap focus to work effectively.

However, if you are doing sports photography for instance, you are imaging subjects that are much bigger and a lot further away.

A 500mm f4 on an FX body has over 2 meters depth of field at f5.6 when focused at 40 meters.  Take a baseball match for instance – not that I’ve ever covered one mind!

Set the single AF sensor focus distance at home plate.

Then tilt the camera up slightly, or move the sensor with the Dpad so it can’t see/is not overlaying what you just focused on. Hold the shutter button down and wait for a player to make a dive for home plate.  As he enters the area of the AF sensor the camera will fire continually if you’re in continuous shooting mode, and will only stop when the camera detects focus has been lost.

Works like a charm!

The key thing is that the depth of field generated by the focus distance makes trap focus work for you – at much shorter distances where depth of field is down to an inch or so if you’re lucky, then couple that with a fast subject approach speed, and trap focus will fall down as a reliable method.

If I’m doing studio flash work like this:

which is never often enough any more! – I sometimes find it useful to use trap focus because it can help doing hand held work under the lowish flash unit modelling lights when you want to make sure eyes are sharp.

Using Trap Focus in a sort of ‘bastardised’ manner can help you maintain sharp focus on models eyes whilst giving you freedom to move around, change composition, zoom etc. by controlling the sharpness of the image with the lens focus ring.

Like I said earlier, it’s a technique that can get you out of trouble every now and again, but up until today you hadn’t got recourse to it on the D4.

But you seriously need to understand the limitations of trap focus deployment before you rush out and use it – you could be very disappointed with the results, and it’ll be all your own fault for trying to bang a square peg through a round hole.

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