XSi (450D) with new 50mm f/1.8 - focus issues

Started Jun 21, 2012 | Discussions thread
Regular MemberPosts: 421
Re: tested the nifty fifty more on my 5DMKII
In reply to WilbaW, Jun 25, 2012

WilbaW wrote:

Thanks for posting your test results, which are congruous with mine. There's a lot more to the story but the bottom line is, this is an optical problem (how the AF sensor sees the subject through this lens), not a focus mechanism problem.

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Check out the unofficial Rebel forum FAQ - http://snipurl.com/RebelFAQ

AF sensor is located at the bottom of the camera, signals "picked-up" by this sensor are amplified so that AF servo can work correctly, these signals must have correct amplitude; otherwise either the clipping will occur (close to Vcc/Vdd), or the signal will be "buried" in noise( not “enough” signal for AF servo to work correctly). The latter actually does not happen because AF sensor always obtains the signal with the lens fully open. However, the former is a real issue!

With fast lenses, there must be some mechanism to prevent clipping (saturation), i.e. some sort of signal attenuation.... right? I think that point is =

Anyway, I found that if you have more than one canon lens, buying canon body that does not have manual focus adjustment means only one thing -> flashing the money down the toilet.

Even the bodies that have manual focus adjustment can “adjust” for correct focus only at one “end”


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