2010 - Week 19, Back Button Focus

Our Street
May 16, 2010 11:28 am
Nikon D90, 50mm 1.8 - shot in RAW
Manual, No Flash, ISO 100, SS 1/2500, f/2.8
Pattern Metering, AF-C, back-button-focusing

I admit, I was last-minute-Lucy this week and didn't think of anything to photograph until today and this is technically pushing the limit for qualifying to part of week 19.

Almost all DSLRs offer the capability to program another button to act as the focus button instead of pressing the shutter half-way. As this button is on the back of the camera (on lower end Nikons you program the AE-L/AF-L button - the higher end ones have a dedicated button already), it is called back button focus or BBF.

When I first starting shooting in manual I used this method a lot, especially in AF-C (continuous focus) mode. I could keep the focus point on one eye and then wait for the smile to press the shutter. This mode is great for on the move toddlers as long as you can pan your camera with them you keep them in focus and then wait for the right moment to actually capture an image.

For a little while I was using aperture priority mode - which is quite fabulous, but then I actually needed my AE-L button to lock exposure for me so I could use spot metering, expose for skin and then recompose the whole photo without the camera changing the overall exposure.

Since the girls were going to be practicing balancing on their glider bikes this was a good time to try AF-C and back button focus again. So I could grab focus on them as they were coming down the hill, but wait to close the shutter until they filled the frame. If I had tried AF-S (one shot) chances are the lens could not have focused fast enough for me to push the shutter without them being too far away or already out of the frame, and it might have been blurry or the camera would not have been able to find focus at all because of the movement. The full sun wasn't ideal, but the results aren't too bad.

If the girls hadn't been so ready to quit because they were sweaty it would have been interesting to try to increase the f/stop enough to push the shutter speed slow enough to try and capture some movement. Without streamers or anything on the bikes, it's hard to tell that the bikes are in motion, except for the few pieces of hair.






post-processing
It's very hard for me to chimp (look at the LCD) in full sun, and even though the overall exposure was pretty good, I did some minor tweaks to exposure in ACR (overexposing the sky a bit more to lighten the subject), and then selectivly masked and brightened/lightened parts of the faces and body.