Monday, 29 December 2008

Microadjustment of Canon lenses

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The Canon EOS 5D Mark II allows you to microadjust the autofocus system for each of your lenses. I followed the method described by Keith Cooper on his excellent website. It's based upon moire patterns produced by interference and is very straightforward to carry out.

These are the results I obtained for my lenses:

Canon EF fisheye 15mm f/2.8 -4
Canon EF 16-35mm f/2.8 L -2
Canon EF 24-70mm f/2.8 L +10
Canon EF 35mm f/1.4 L -2
Canon EF 85mm f/1.2 L -4
Canon EF 170-200mm f/2.8 L 0
Canon EF 100mm f/2.8 0

All minor tweaks except for the 24-70mm zoom. I then shot a test image, with and without the microadjustment, for each of the lenses to see if there was any visible difference.

I used the above test card which came free with an issue of Digital Camera magazine. It was firmly clamped, to ensure no movement, and the camera was mounted on a tripod, triggered by remote shutter release, with mirror lock-up activated.

Above is an enlargement of the card from shots taken with the 24-70mm zoom lens, with no microadjustment on the left and with the +10 adjustment applied on the right. The image on the right is clearly the sharper of the two. It took about 90 minutes to adjust and test all my lenses and was well worth the effort.

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George Bain said...

Hi David,

Yes this method seems easy to use, but what distance did you use from the screen depending on the lens - does it matter?

What camera settings too, does that make a difference?

Thank you

David said...

Hi George,

The closer you get the better. Remember than many lenses have quite significant minimum focusing distances though. If you're calibrating a zoom lens, set it to the longest focal length you can.

You need to use 'LiveView' to perform the calibration.



Richard Slater said...

David, I've spent a good amount of time on this to find a perfect way of doing it to avoid any compromise. I would suggest the following steps.

1. Make sure the chart is showing at 100% on your LCD screen. Use a calibrated monitor.
2. Set up your camera so it is level with the screen at all angles. Avoid any tilt on your monitor.
3. Set camera to manual mode. Go ISO 400. Centre-weighted average (to match live view mode). Single shot. Widest F stop available. Also set your white balance to match your environment.
4. Go live view and focus in quick mode. You will probably see flickering banding across your 5D screen due to refesh rate of your monitor, so turn up the +ev dial until this is gone (you will be able to see the chart better and have a decent exposure.
5. Adjust manual focus until you see the most moire patterns (rings) - now fully magnify the 5D view and fine focus further until you can see the texture/pixels of your screen. Well I can anyway...
6. Exit live view and press auto-focus while watching the lens window dial. If it moves even slightly you'll need to enter a + or - (front or back focus) value into your 5DMk2 lens adjustment menu.
7. Repeat steps 5 and 6 until happy. I find that when perfect auto-focus is obtained you will not even HEAR the lens motor try to adjust focus when pressing the shutter, just the beep.
8. If tuning a zoom lens start calibration on the long end, but do repeat calibration at both ends of the range - you might need to compromise.

This will keep the pixel peepers happy.


David said...

Hi Richard,

Thank you very much for sharing this with us. I think you were even more thorough than I was!