Best way to set up "micro adjustments" for a lens on a 50D

Started Apr 25, 2010 | Discussions thread
new63
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Re: Best way to set up "micro adjustments" for a lens on a 50D
In reply to Pyrie, Apr 25, 2010

I tried this but was not very successful. I found tethering a little cumbersome in execution especially when trying to calibrate long prime 300 and up.

here is a method I used and was simple and it worked.

I used my backyard and window pane. Window pane 's plane is quite flat and good.

what you need is the following

flat vertical surface
Tripod with level
a spirit level for 50D ( for &d not required)

Letter sized focus chart or any printed paper with good contract. I used my kids picnic trip flier which contained pictures different fonts etc in black and white.

1 - setup the Tripod at 25-50X focal length

2 - I used about 50X the focal length for the distance (if you have the space, if not above 25 X is good)
3 - Set the height of the tripod at your eye level.
4 - level the tripod.

5 - For 7D mount the camera and ensure the 7D level is correct. For other model use the spirit level on the Tripod head to make sure it is level specially if you are using ball head. Then mount the camera.

6 - tape the focus paper 0n the vertical surface, such that the center focus point of the camera is approximately on the center of the page. you can actually use any other focus point also not necessary to use the center point only in case of 7D.

7 - make sure the paper is taped smooth and plain on the vertical surface. that is the reason I used a window glass.

8 - lock down the setting tight and set your lens at widest aperture.
9 - set MLU

10 - focus using the center point and take shots at different MA starting with 0.
11 - after each MA change ensure you defocus the lens.
12 - view the shots in DPP. pick the point where the image is the sharp.
13 Repeat the above few times to make sure the result is consistent.

On my 300 .28 lens I found some thing very strange, it required +3 MA. however, when I compared the image from 0, +1 +2 and +3 0 was sharper than 1 and 2 but not as sharp as the 3. so make no assumption that the focus will improve linearly.

another important point to remember at least with 7D, after 300 MM was calibrated, when 2X TC was added you have to dial in the MA again (+3 in this case) for the combination. The camera treats this combine as a different lens (600mm).

My other lens 50 1.4, 70-200 2.8 did not require any adjustment.

Hope you find this useful

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