For anyone who is interested, the following is an update to my earlier post concerning back button focusing on DSLR cameras. For a quick refresh or for those who don’t know, what it is all about is that the majority of digital cameras have a two stage shutter button, half press focuses and meters the scene the camera is pointing at, full press takes the picture.
On DSLR cameras and particularly if you are shooting moving objects, there can be significant advantages to separating those two functions which is possible by reassigning functions using the cameras menu system. So as I have been practising this technique, the following is my comments plus some picture examples.
My Starting Setup
The following picture is of two of my ‘previous generation’ Canon cameras, a 450D and a 40D which I set up for trying this out before configuring my current cameras to do the same thing. As I wrote previously, as I have my current cameras set up the way I want, I didn’t want to mess them up so I used my older ones first.
As I use Canon cameras, my comments are specific to them but the basic process should be possible on any DSLR. Canon divide their DSLRs into three main categories, Consumer, Enthusiast and Professional. Basically whilst at the ‘Pro’ end everything is totally configurable, as you come down the range, options are fewer, control systems are simplified and are as automated as possible whilst still leaving plenty of scope for full manual control.
Of these two cameras, the 450D fits into the ‘consumer’ category and is actually physically smaller. It may look a bit bigger than the camera is but this is because this particular one has a battery pack on the bottom. On the right hand is the 40D which is an ‘enthusiast’ type model and this actually has a dedicated AF button on the back which the 450D doesn’t, you have to reprogram another button to act as AF, the 40D camera is also bigger than the 450D.
The reason I mention the sizes is that I found that despite me having quite small hands, the larger 40D was easier to handle than the smaller 450D in this trial and to be honest, I’m not sure why that should be but it is worth mentioning in passing. Another thing worth a mention is that the configuration is done via the “Custom Setting” menus and there are many choices available here, one of which covers “Operation/Others” but conveniently there is also there a “Clear Custom Settings” which resets the camera, useful providing you don’t have other custom settings in force which you want to keep.
My experience of using the 450D in this way were such that I reset the camera by clearing the custom functions and decided not to bother setting up back button on its replacement, an even smaller 100D. However, my experiences with the 40D were very positive so I did set the AF button on its replacement a 7D and it works very well indeed. The 7D has far more advanced metering options than the 40D so other possibilities arise but I am still experimenting with those variations.
The summary to what is happening goes like this: These cameras tend to have two drive/focus modes “Single Shot” for static subjects, “Servo” for tracking moving subjects and a third hybrid mode that starts out as single shot but switches to servo mode if the subject moves, I’ve never had much joy with this latter mode.
What this back button focus mode does is allow you to use the AF button as a “Single Shot” you focus on the static subject, press the AF button to acquire focus and you can then release and re frame if you like, it will keep the focus. If the subject is moving, you put the focus point on your subject whilst keeping the AF button depressed, it will track as in “Servo Mode”.
The Following Gallery
This sequence was taken using my 7D and although I took a number of others, this sequence is pretty representative of all of them. It was pretty gloomy and I was shooting at ISO 800, it is the same bird, a Tern who was looking for a fish breakfast. He was circling over the estuary of the River Brue so coming towards me and moving away which is a good test of the “Servo Mode” using the AF back button. The gallery is set up to show the ‘context’ of each picture then a closer up crop of the same image to show the focus.