Sunday, 18 March 2012

Canon 7D Front Focusing Problem

Whilst I have had some reasonable pictures with the 7D I haven’t been totally satisfied with the results. At first I thought it was my technique that was wanting because the lens I purchased (Canon 400mm f5.6) does not have IS. I had also read somewhere that the 7D requires a heavier hand on the sharpening to get the desired results and indeed I have had to resort to this on most of the images I have  posted on Flickr.  Whilst heavy sharpening can often improve the image the results are never the same as a  picture that started off sharp and heavy sharpening increases the noise quite markedly .......... but that’s another problem.
A month or so ago on a rainy day with the Slavonian grebe in Dover marina I did a side by side comparison of the Sony and the Canon and without doubt the Sony was the best. As I'd only just got the Canon I attributed this to the lack of IS on the Canon and the slow shutter speeds I was experiencing.
On one of my days on the cliffs with the perched peregrine I did another side my side comparison and on this occasion although the Canon produced the superior images I was still a little disappointed with the results especially when cropped in close. As before there was a softness to all the images even though this time the pictures were all were taken using a tripod and I had good shutter speeds.
The outcome of these comparisons and problems made me reluctant to take the Canon out on dull days and if/when I did I was resigned to using a tripod and high ISO (to keep the shutter speed high).
Having spent so long in deciding what to buy to replace the Sony I didn’t want to admit to making a mistake in purchasing the Canon - not just because of the money wasted but because I had no idea what to change it for.  So had I wasted my money? Today I set out to find out.
My first test on the accuracy of the focusing was to use a method suggested by Steve Ashton whereby you set up at ruler at 45 degrees then focus on one of the central numbers. I took a number of shots at different shutter speed and every single one suggested I had a front focusing issue i.e. the number I was focusing on was not the sharpest it was several centimetres down the ruler..
I searched the internet and found a test target (published by Tim Jackson) that I printed off, set up and ran some more test. The test chart is marked up to show how bad the back/front focusing is - with the right hand side being further away from the camnera This test showed I had a significant  front focusing problem - of the order of 10-20mm.(I did a lot of shots at different shutter speed but I needn’t have bothered – they all showed the effect):

Focus was on the thick black line
 Out with the manual and after several changes to the autofocus microfocus adjustment I think I have overcome the problem:

Post adjusting
Fingers crossed.
Sunday. As the sun was shining I went along the cliff tops from South Foreland to Langdon Hole looking to find something to point the camera at (hoping for a peregrine) to test whether the adjustments would have an effect in the field.
There was a not a lot going on but mippit numbers have increased over the last few days and were singing/displaying with gusto but the first test subject was a male stonechat. He never let me get really close but the results were far far sharper than I had grown to expect (I’ve put an uncropped version up so you can see the level of cropping done on the close up):

Uncropped

Stonechat
When at Langdon Hole I spotted 2 peregrines circling just above the cliff top back towards Fan Bay so I returned to near the rock fall and waited. I didn’t have to wait too long before one did several passes:

Peregrine
Whilst waiting for the peregrine to come close one of the herring gulls seemed to take exception to the presence of the peregrines and pestered one of them for about 5 minutes but sadly always distant:
Herring gull attacking peregrine
On the return leg there was a male wheatear down in Fan Bay but I couldn’t be bothered to climb down to try and get some pictures but a mippit did let me get reasonably close and again the shots are much better than I’ve experienced previously.

Meadow Pipit
So not an exciting day bird wise but it’s a relief that the camera is now operating how I’d hoped it would.
(Click on any image to get them all at a larger size)

7 comments:

  1. You may have just adjusted the camera to suit your current lens. Does the Camera give good results with other lenses now its been adjusted ? Just a thought.

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    1. Warren, You may be right but it's the only lens I have so I can't put it to the test.
      My only doubt is that the manual states(in bold) "Normally this adjustment is not required. Do this adjustment only if necessary" which to me sounds like it should not have required adjusting.

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  2. I read that front focussing can be an issue, and I have had a 7d that suffered with this, although I never knew the problem at the time. It definately looks like your camera is front focussing from your tests, how far did you have to move the dial to sort the problem, from 0 to 15. You can sent the camera back under warranty if you so wished, but if the micro adjustment does the trick, alls well. You are right though, they should not need re setting but it is a simple exercise to fix in the Canon workshop and you would not have to pay for it. In my opinion, Canon aftersales are one of the best.

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  3. Hi Steve,

    My son in law has suggested to me that i may have a similar issue to yours. I would be interested to hear from you by separate e mail where you got the test target off the internet and what was required to fix it. I have also read the manual suggesting that " it should not normally be necessary" . Also like Steve to what extent did you need to shift it and in which direction? Maybe when I get back from Norfolk i will ring you to discuss further.

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  4. glad you got it sorted out,no such issues with 60d only if you drop them

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  5. hello, what focus change you done with 7D and 400mm 5.6L?
    +5 or +10 or?:) i have that same problem.. please

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  6. Thanks for review, it was excellent and very informative.nice blog..
    thank you :)

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