Thursday 18 February 2010

Gear Review - Canon 7D AF System

As I promised a couple of days ago in this blogpost, I would add my views on the Canon 7D AF system based on my experiences 'hands on' with it.  My thoughts are based on comparisons with my 1Dmk111 and I used the 7D in the same vein to ensure true comparison.

The 7D is equipped with 19 cross type AF points, with only the centre point having f2.8 sensitivity, which helps determine my thinking in the way I set up for use with my longer lenses.

In terms of mode, there is One Shot for still subjects, AI servo for moving subjects and AI Focus for still subjects that might move.  I dont tend to bother with AI Focus.  If it had a decent purpose  in life, they would put it on the 1 series, which they don't.

AF points can be selected either singly, grouped by Zone or letting the camera do it for you with Auto.

I have only used single point as it is what I am used to, and allows me to place the AF point exactly where I want it on the subject.

With Zone AF, you can select groups of four points at the top, bottom or on the sides of the group, or the central block of 9.  Again I have not trialled this.  It might work for some subjects, but my concern with long lenses wide open, is that the nearest part of the subject will be grabbed by the group.  This might work OK with a small subject, but for a large bird in flight for example, you could end up grabbing the wing tip rather than the head.

I never bother with Auto, as I like to maintain the control.

An additional option with the single point  mode is Spot AF.  The AF point is actually quite a large area, much larger than the little black or red square in the viewfinder, so for more accurate focussing the Spot AF can allow you to be more accurate.

When I carried out this test in this blogpost, I used AI servo with centre point.

But that is not where it ends.  Many of the better functions hidden away in the Custom functions have been carried over from the 1Dmk111.  These include the AI servo tracking sensitivity, which I tend to use a one click left of centre towards slow, and works OK for me on both the 7D and 1Dmk111. C.Fn 111-3 works better on the 7D in my opinion, and the gull test shots demonstrate that extremely well, again I set it to Continuous for birds in flight.

I didnt have the time to mess about with lens micro adjustment, but I think the only way to get this done properly is by Canon in the lab, with the lenses you intend using on it.  I had this done on the 1D and it helped.  The 7D gives you the opportunity to mess about if you wish and it might worth using the facility to check, and if your lenses are off then send them to Canon to get it done properly.

Dave's recent post covers some thoughts on this in more detail.

One useful little function is the ability to let the camera shift the AF point to the corresponding location when you switch shooting from landscape to portrait format.  For example, if you are using the top right point in landscape, it would become top left when you switch to the top left as you rotate the camera anticlockwise.  With this function, it will keep the top right AF point selected for you.

One change you have to get used to as a 1D shooter is if you want to select the AF assist points.  You don't go into the Custom Functions.
You need to go to the Q in a square button, toggle to the AF area on the back screen, then pressing the M. fn button next to the shutter button, you scroll through to the various AF mode choices, and one of these will give you the AF assist points option.  You need to remember if you want to make the change in a hurry.

Unlike the 1D though, you only have the choice of all surrounding points to do the AF assist function.

As I mentioned in my original AF testing blogpost, the AF system on this camera is quite excellent and very easy to use with consistent results.  However, there is a much greater level of sophistication when stepping up from any of the XXD or XXXD series Canon bodies.  This is why I think many of these users have been having difficulties and blaming the camera.

With some hard won 1Dmk111 experience under your belt, you would be very happy with the results.

This makes the 7D a good back up to a 1 series.

In the next part, I will cover off some of the ISO and noise issues that I see that some people have experienced.  I have not seen these issues based on how I shoot and then post process, so will share my thoughts in the next installment.

So that was our 500th post since we started over a year ago.  How time has flown by.

I have to say I was most upset while writing this particular post as I had got about two thirds of the way through when I lost everything I had typed.  Normally Blogger autosaves, and I believed it had but something went wrong.  So after much gnashing of teeth and a few choice words, I had to start over again.

Anyway we got there.  Looking forwards, I should be able to get out taking some photos over the weekend, so should have some more new material to share with you.  Roll on the lighter nights and mornings too.

Goshawks are on the agenda - if they come close enough



  1. great post very usefull as i am looking for a mk111 back up

  2. I am really thinking of getting a 7D either to replace my MKII or as an addition.
    Great post, it has helped A LOT!!

  3. Thanks Martin, very helpful post and interesting to compare to 1D3. Do you see the lack of flexibility with the AF assist selection in 7D cif 1D3, an important forfeit, or is it something that could be lived with for the majority of situations bearing in mind the cost difference?
    Kind regards