Saturday, January 8, 2011

Utilizing the Focus Micro-adjust of the Canon 7D

I have attempted to utilize the micro-adjust on my Canon 7D for the four lenses I own. I was not quite sure how do do this, so I just made it up.

My technique was to stretch a tape measure along the dining room table, and put a high-contrast card vertical to the table next to a specific mark on the tape measure (e.g., the 16-inch mark, which is red on my tape).

Then I put the camera on a tripod, set it to ASA 100, and set the camera to "A" mode with the widest aperture possible. Finally, I set it up to do a mirror lockup and a 10 second delay.

Examining each picture, I look for the shot with the card in focus, along with the "16" mark on the tape. And also the "15" and the "17" on the tape needs to be the same amount of out of focus. (For the 11-16 Tokina, the widest aperture kept at least four inch marks in color. The Canon 50 was the most dramatic, of course.)

I have created a Picasa web album of the final set of photos, and you can find it here.

Canon7D Micro Focus Adjust

Here are some typical pictures from this process.

The final setting for the 55-250mm lens (+10)

My 50mm f1.8 set to +20

My 50mm f1.8 set to +15

My 50mm f1.8 set to +10

The final result I record here, as much for my own benefit as anything else.

Canon EF-S 18-55 -- +8
Canon EF-S 55-250 -- +10
Canon EF 50mm f1.8 -- +19 (!!!)
Tokina 11-16 f2.8 -- +10

So, every lens is off in the same direction. These numbers mean that the camera will make the focus point too close to the camera. Moving the adjustment positive moves the focus point towards infinity (away from the camera).

I really do not know if this is a function of the lens or to camera or both. But I am astounded that all of my lenses are so far off from what I presumed (being "Canon quality" (whatever)) they would be: a value of zero.

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