From: | John |
Sent on: | Monday, January 5, 2009, 5:05 PM |
What is the best way to use the Micro Focus Adjustment?
The question is simple enough, but the answer really depends on the lenses you're using and the way you use them. To begin with, it should be clarified that there are two types of in-camera AF microadjustment for the EOS-1Ds Mark III and EOS-1D Mark III cameras:the first adjusts the point of focus equally for all Canon EF lenses, whereas the second adjusts the point of focus for up to 20 individual lens types, at one adjustment per lens. In both cases, the point of focus can be adjusted up to +/- 20 steps in 1-step increments. Also in both cases, any adjustments you make apply only to the specific camera body in question; lenses themselves are never modified by the camera's AF microadjustment settings. The amount of focus adjustment per step is proportional to the maximum aperture of the lens, with the goal being to increase the precision of the adjustment with large aperture lenses since they have a smaller depth of focus. With all that as a preamble, here is an unofficial procedure for selecting and using an AF microadjustment setting:
Here are a few additional precautions to observe:
? Do not attempt to autofocus on an angled chart, because doing so will degrade the consistency of the camera's focusing measurement. Keep in mind that the camera's AF sensor is comprised of multiple pairs of linear pixel arrays. If you attempt to autofocus on a single line in an angled focusing chart, only a few pixels from each active pixel array will "see" the target. Ideally, the contrast in the reference target should cover the entire area of the camera's center focusing point, and the reference target should be perfectly parallel to the camera's focal plane.
? For best results, manually set the focus on the lens to infinity for every exposure before allowing the camera to autofocus the reference target.
? Expect some minor variations in focusing accuracy within each set of three test images, even though they were all taken at the same microadjustment setting. This is completely normal, and is due to the tolerances of the camera's AF system.
? Expect smaller microadjustment settings to have a greater effect with telephoto lenses, and vice versa for wide-angle lenses.
? If you are attempting to set microadjustments for a zoom lens, it is important to realize that the camera's setting may only be accurate for the focal length setting you test. The instruction book suggests testing at the longest focal length of the lens, but you may find it more efficient to choose the focal length you use most often.
? Some EOS cameras and some EF zoom lenses may require more sophisticated calibration than the in-camera AF microadjustment settings can provide. In such cases, it may be necessary to have calibrations performed at a Canon Factory Service Center.
? Last but not least, there is no "official" Canon method for setting AF microadjustments, so this procedure is unofficial. If you think you can do better, then by all means, go for it. Towards that end, be advised that some independently made tools are designed to help you set AF microadjustments accurately. One of these is the LensAlign kit, due out soon from RawWorkflow.com:
About the 1/focal [length] rule of thumb [for full-frame sensors] vs. the 1.6x crop factor: As the crop-factor sensor picks only the center part of the full image and the real focal length of the lens remains the same, how does shooting with a crop factor body differ from shooting with a full-frame and cropping the center part in post-processing? With a 50mm lens, wouldn't exposing at 1/50 s on both bodies yield the same results after cropping the biggest image? It's not as if the focal length of the lens has been directly modified, like, for instance, with an extender...
For the sake of readers who may be unfamiliar with the concept, I assume you're referring to the often repeated recommendations for minimum shutter speed to achieve blur-free hand-held photography. If so, you're correct that the degree of camera shake at the focal plane is the same for any given focal length regardless of the imaging format when all else is equal. However, you may not have taken into account the magnification factor for the final output, for example, a print. If the full-frame image is cropped to match the smaller imaging format as you suggest, then the advantage of the additional imaging area which could have been used to reduce the magnification factor of the resulting print is lost. On the other hand, if output size is equalized and the full frame is used, then lower magnification will reduce the visibility of blur in the print. That's why the 1.6x conversion factor should be applied to the 1/focal length shutter speed rule if you're using an APS-C sensor camera and you want to play it safe. If you want to play it even safer, use a camera or lens with an image stabilization system.
What is the micro-adjustment ?
From: Conrad Tan <[address removed]>
To: [address removed]
Sent: Monday, January 5,[masked]:39:39 PM
Subject: Re: [photo-413] New Meetup: January 2009 Social!
Cool! If anyone knows how to do the micro-adjustment on the new 5D Mark II please let me know. I'll bring it. Thanks in advance!
On Mon, Jan 5, 2009 at 2:44 PM, Reese <[address removed]> wrote:
Announcing a new Meetup for The South Bay Photography Meetup Group!
What: January 2009 Social!
When: January 21,[masked]:00 PM
Where: Click the link below to find out!
Meetup Description: Hey SBP!
Happy New Year!
That's right, it's time for the monthly social. As usual, there's no set agenda and the meeting is more of a social mixer type thing.
Photo Challenge
This month's challenge: Landscapes!
Bring your favourite prints to the meeting and show it off to the group. Discuss photography techniques, ask questions, share tips, and talk gear!
See you all there!
- Reese
Learn more here:
http://photo.meetup.com/413/calendar/9452539/
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632 Broadway, New York, NY 10012 USA
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