11-02-2011, 10:20 AM
Lens decentering generally is much more obviosu at close ranges than at long ones.
My method of testing is to shoot at different apertures, at different zoom lengths if it is a zoom lens, of a more or less evenly lit, flat object preferably with plenty of detail, like a brick wall or newspaper flat on the ground or so, head on, camera sensor parallel to the object.
I don't worry too much about sharpness when doing this test, but whther the corners and edges are equally sharp. With decentering you will often find that one edge, corner or a part thereof is clearly less sharp than the rest. And you may also find that it is possible to get that one area sharp by manually focusing, but then the rest of the image will be unsharp.
Personally I have encountered this only twice so far, once with an 85 F/1.8 and a TS-E 45 <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.
BTW, I have seen a lens where it was a weird streak from the mid quarter left to the centre of the image once; that was a zoom lens. I guess with zoom lenses decentering can well be more complicated in nature due to the many different elements and their complex movements than with primes.
Generally, you will likely find that the area affected by decentering is anywhere from about 2 to 20% of the image, and in bad cases it will not disappear when stopping down. With the 85 I mentioned above it was still visible on APS-C at F/11, with the TS-E it disappeared at F/8.
In short, check for an even fall-off in sharpness (and vignetting, also an indicator) from the centre towards the edges and corners. Also check at various apertures, to see how it behaves wide open and stopped down.
Once you have seen decentering once or twice, you'll generally recognize it with just a few shots.
HTH, kind regards, Wim
My method of testing is to shoot at different apertures, at different zoom lengths if it is a zoom lens, of a more or less evenly lit, flat object preferably with plenty of detail, like a brick wall or newspaper flat on the ground or so, head on, camera sensor parallel to the object.
I don't worry too much about sharpness when doing this test, but whther the corners and edges are equally sharp. With decentering you will often find that one edge, corner or a part thereof is clearly less sharp than the rest. And you may also find that it is possible to get that one area sharp by manually focusing, but then the rest of the image will be unsharp.
Personally I have encountered this only twice so far, once with an 85 F/1.8 and a TS-E 45 <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />. BTW, I have seen a lens where it was a weird streak from the mid quarter left to the centre of the image once; that was a zoom lens. I guess with zoom lenses decentering can well be more complicated in nature due to the many different elements and their complex movements than with primes.
Generally, you will likely find that the area affected by decentering is anywhere from about 2 to 20% of the image, and in bad cases it will not disappear when stopping down. With the 85 I mentioned above it was still visible on APS-C at F/11, with the TS-E it disappeared at F/8.
In short, check for an even fall-off in sharpness (and vignetting, also an indicator) from the centre towards the edges and corners. Also check at various apertures, to see how it behaves wide open and stopped down.
Once you have seen decentering once or twice, you'll generally recognize it with just a few shots.
HTH, kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....