microadjustment for the mentally challenged

Hi all.
Yes, the mentally challenged one here is me.
I read up a bit prior to jumping into the waters of microadjustment on the 7D and my tamron 28-75 (my only lens currently)
and boy do I feel completely confused.

I found two charts (thinking I was the overacheiver) - one which I printed had numbers and was supposed to be shot at a 45 degree incline

the other a moire pattern that you are supposed to shoot on your computer screen - some say at "an angle" and some say at 90 degrees perpendicular

then you are supposed to pixel peep (isn' that against the law!?) to see which adjustment gives you the best picture.

ok, so why should I do this in the first place? because it was my impression that the area that the AF locked on was not sharp enough even stopped down.

then I followed the instructions each gave (assuming they weren't conflicting) and viola- nada. every time I used the chart at 45 degrees (i even freaking measured the 45 degrees)

and in the end the only thing I can say is that -10 and +10 doesn't SEEM to be right.

Can anyone offer some practical help?

Thanks

Use a contrasty, well lit focus target that is square on to the camera and at least 3X wider and taller than the indicated focus point in the viewfinder. That will make sure the camera has an unambiguous target upon which to focus. Use an angled rule/scale to check exactly the place where focus is achieved and to help guide you to work out which way to adjust and by how much.

You can get more information on the procedure from an old article by Chuck Westfall. Scroll down a little on this page - http://digitaljournali​st.org/issue0812/tech-tips.html - to the second article.

You might also find the demonstration videos on the Lens Align website helpful - http://videos.lensalig​n.com …-User-Guide/6830310_fnpyr.

Here is my version of a focus target and scale. The box is large enough to more than cover the centre focus point and has plenty of contrast for the AF to lock on to and from which to judge sharpness. As you will see from this example the lens is front focused slightly....

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Hi Tim,

Thanks for the answer. In the picture that you attached, what was the point of focus? Is this the correctly adjusted picture or before the adjustment?

And in general if i can ask:
if you zoom in on a picture using the LCD in the back of the camera - does it get to an equivalent of 100% (full zoom of course) - i.e. can I use it instead of running back and forth between camera and computer?

I focused dead centre on the blue/green and white box. That meant there was no possibility for the AF to be confused and try to focus on anything other than the flat side of the box facing the camera.

The closeup image is prior to calibration, with microadjustment still at 0. The sharpest point on the ruler should be at the 30cm mark. Clearly the sharpest point is around the 28cm mark. The lens is front focusing and adjustment is needed. I do not recall the exact adjustment I needed to make and I do not have any pictures showing the results after adjustment. I only took this picture to show the setup.

I don't know how viewing the LCD screen at 10X zoom compares with viewing an actual 100% view at a computer, but so long as you can distinguish the sharpest point of focus, and whereabouts the depth of field is distributed, then that is sufficient. With a narrow enough DOF, such as that shown above, it would be easy enough to make a determination from the camera's LCD screen. Optionally, if you can shoot with a tethered connection, you could have the images appear on the computer screen as you shoot.

I might add that the same lens showed a similar amount of front focus on another camera, which I also microadjusted using the same test rig.