<p>The purple (or red, blue, yellow, green, etc) fringing is normal for most lenses, especially zooms. Magnification is slighly different for each wavelength of light. On good lenses, programs like Lightroom 3 or the new ACR in Photoshop CS5 can correct it automatically and it makes an amazing difference in edge sharpness (especially in something like tree branches). However, the correction is excellent on the 17-55, 17-40 and 24-105 but on an inexpensive 75-300 or even on the 18-55 II kit lens, I could never fully correct it. It was unbalanced from side to side so I had to choose a side, or process seperately and merge (a pain to be sure).<br>
Not sure how different the 70-300 is from the 75-300 but I saw the same reults as you. On the original Rebel it wasn't so bad and I even managed a cover photo with it. Nor did it seem too bad on the 30d but on the 5dmII it is awful. No sharpness, lack of contrast and that purple/green fringing that can't be fully corrected.<br>
You didn't say what body you are using but my 17-55 held sharpness fairly well to the edges on a 30d (8MP). Of course i couldn't try it on the 5dmII but it is purported to be one of if not the best non-L lens Canon makes.<br>
A B&W image as you used is a demanding test for sharpness, in the real world you may notice less difference from the center to edges.<br>
Remember too that all raw images need a little bit of sharpening to compensate for losses in the de-mosaicing process as well as lens loss. A little sharpening will probably make a big difference in your 17-55 test. And finally, most images will not look perfect at the 100% zoom level.<br>
Are my lenses rubbish? (examples inside)
in Canon EOS Mount
Posted
<p>The purple (or red, blue, yellow, green, etc) fringing is normal for most lenses, especially zooms. Magnification is slighly different for each wavelength of light. On good lenses, programs like Lightroom 3 or the new ACR in Photoshop CS5 can correct it automatically and it makes an amazing difference in edge sharpness (especially in something like tree branches). However, the correction is excellent on the 17-55, 17-40 and 24-105 but on an inexpensive 75-300 or even on the 18-55 II kit lens, I could never fully correct it. It was unbalanced from side to side so I had to choose a side, or process seperately and merge (a pain to be sure).<br>
Not sure how different the 70-300 is from the 75-300 but I saw the same reults as you. On the original Rebel it wasn't so bad and I even managed a cover photo with it. Nor did it seem too bad on the 30d but on the 5dmII it is awful. No sharpness, lack of contrast and that purple/green fringing that can't be fully corrected.<br>
You didn't say what body you are using but my 17-55 held sharpness fairly well to the edges on a 30d (8MP). Of course i couldn't try it on the 5dmII but it is purported to be one of if not the best non-L lens Canon makes.<br>
A B&W image as you used is a demanding test for sharpness, in the real world you may notice less difference from the center to edges.<br>
Remember too that all raw images need a little bit of sharpening to compensate for losses in the de-mosaicing process as well as lens loss. A little sharpening will probably make a big difference in your 17-55 test. And finally, most images will not look perfect at the 100% zoom level.<br>
Hope I helped,<br>
Joel</p>