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01-09-2009, 05:14 AM   #1
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The term "De-centering fault"

I've occasionally seen that a particular copy of a lens suffers from a decentering fault.

1. What does this mean?
2. Is it visible on real world photos, or only on pictures of test charts?
3. If the former, can you post examples of photos exhibiting this fault.

Dan.


Last edited by dosdan; 01-09-2009 at 05:24 AM.
01-09-2009, 05:27 AM   #2
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I am not an expert on all of this, but I think this image shows it well

Flickr Photo Download: Scammell Amazon 6x4

The right side lights and fender is sharp and the left very soft. The plane of focus runs through both of them, so they should both be sharp.


Last edited by pcarfan; 01-09-2009 at 05:33 AM.
01-09-2009, 05:37 AM   #3
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pcarfan, that's horrible. I wonder it that's a representative example of this fault or an extreme case.

Dan.
01-09-2009, 05:46 AM   #4
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I found that image just surfing through some flickr pictures. As we don't know the story behind the shot, it is all guesses. It could even be post-processed to look that way

But, if you place the camera parallel to a newspaper and shoot, so that the plane of focus is on the paper, then you can compare the image to see whether it has this centering/de-centering defect.

01-09-2009, 08:24 AM   #5
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A decentered lens shows a Red X?
01-09-2009, 10:12 AM   #6
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De-centered means that one or more elements are not properly aligned. This can be a matter of position or angle. When present, it is an indication of poor manufacturing process and/or poor quality control. Since it is a common issue with the DA* 16-50, one must wonder what is going on in the Pentax factories in Vietnam.

Steve
01-09-2009, 11:28 AM   #7
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QuoteOriginally posted by dosdan Quote
pcarfan, that's horrible. I wonder it that's a representative example of this fault or an extreme case.

Dan.
One of my DA*16-50s was as bad as that. I went through 3 before giving up.
01-09-2009, 08:15 PM   #8
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Man, that pic gives me a headache.

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