Will Patterson
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Dawei Ye wrote:
fmikio wrote:
But, how could I check if the adjust I did is ok if I don't use an autofocus ?
Ok but your thread title clearly says "28 f/1.8 Sharpness" not "AF performance" I'm just saying they are two separate issues and if you wanted to confirm whether your lens was sharp or not - use MF first. THEN do your stuff with MA and whatever. It's important to get the temporal sequencing correct and not fudge about with 2 uncontrolled variables in the same test
Who knows whether the softness is caused by the lens being soft, or being out of focus, or both. At least once you have confirmed sharpness with MF, you can be sure that any softness in AF results is due to AF inaccuracy, rather than lens optical issues
Will Patterson wrote:
Fact is, when you use your lens, it's being used in AF mode, not MF. So why not test what it does in AF mode?
This has nothing to do about how the lens is used in practice. It's about identifying the causal reason why performance is not up to scratch. To do this, you have to eliminate conflicting variables. Otherwise, how can you possibly know whether it is because the lens is not optically up to scratch, or whether an AF intolerance is the reason for the softness?
But...But...you say, "I use my lenses as AF lenses." This is besides the point. Being a wedding photographer like yourself, if you take your lens to canon because you think it's not working well - do you expect Canon to send its technicians to a random Wedding on the weekend to do some test shots using AF in order to check the optical specifications of your lens? hey...is that not how the lens is being used? 
The reason MF must be used when testing for lens sharpness is the exact reason why a Tripod is used (to eliminate another factor as a cause (in the tripod's case - motion blur). If you want to test for AF accuracy, then fine, but the topic of the thread is "28mm 1.8 sharpness"
what use is a sharp lens if it isn't focusing accurately?
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It could also be something wrong with that AF point. One way to test if its the lens of the camera AF is to make sure its on the same plane (like the first pic) AF center point on it (half shutter press) and then (I forget the technical point) but move/shift the camera to the right, so that its in the same area as the first shot. I feel stupid, I cannot think of the term right now, OMG.
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