7D - 70D - 7D2

Started Jul 21, 2013 | Discussions thread
Steve Balcombe Forum Pro • Posts: 13,524
In addition...
1

Jerry-astro wrote:

hires wrote:

What is the difference between center point and spot AF? My 550D has center point as did my 30D. From this thread it sounds like the 7D might be the better camera for bird photography with the 400 5.6?

Spot AF is to autofocus as spot metering is metering. It enables you to focus accurately in an area that might be very busy with potential targets. Think, for example, of shooting a small bird sitting on a branch surrounded by foilage. A standard AF sensor is large enough that the surrounding foilage may confuse it and in a situation where you're shooting long with thin DOF, you will not get accurate focus acquisition on the target. With spot AF, the AF sensor is smaller and will have the capability of picking a smaller, high contrast area and hopefully eliminate surrounding clutter that could throw off focus.

Looks like win-win, until you realise that there is a price to be paid for this accuracy - more chance that the smaller AF area will fail to find enough contrast to lock on to. When I first had the 7D I thought it was rather odd that spot AF was disabled, and had to be explicitly enabled using a custom function. But now I think I understand Canon's reasoning - it's Canon's way of saying "use this only if you understand it properly" - a bit like ISO expansion which is also disabled by default.

I do use spot AF, but I often choose manual focus (or FTM) instead for those 'focusing through foliage' situations.

I haven't had the opportunity or need to use it extensively on my 7D, but for those few times where I've needed it, it's been invaluable. There were definitely cases where standard AF simply could not properly acquire a target and the only way to accurately nail the target would be manual focus or spot AF.

Center point simply defines one of the points available for AF. If you have spot AF enabled on the 7D, it can be used with any of the AF points you've selected including the center point.

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