11-28-2010, 02:11 PM
There is a good way and a bad way to "combat" CA (of the measured by PZ variety).
If you are lucky enough to have a lens that has a linear progressing CA from the center to the edge, and the offending wavelength exactly matches the red, or green, or blue channel, you can correct the CA by shrinking or expanding the offending channel. This will increase contrast and will increase "detail". This is the DPP manner, as far as I can figure out.
It is not always that simple, though.
You can also hide the CA colours, by just adjusting the offending coloured edges. This will NOT enhance contrast, and not get back the detail lost by the CA. As far as I can figure, this is what gets done by in-camera CA "correction" like for instance Nikon JPEG output does.
About the 15-85mm and its small max. aperture: genotypewriter is of course exaggerating with his "can do that with a P&S", but he does have a point. Always just having a smaller aperture available WILL just always give you that big DOF standard look, like P&S's always give you too.
Also, what I said before has to do with that.... f5-5.6 in the portrait range really just is not sensible to me. So the 50-85mm range is not great for that. And usually, when I need "tele" I need MORE than 85mm, so it does not make much sense for that either.
So a 17/18-50/55mm f2.8 lens just always makes more sense. You have f2.8 in the portrait range, and will have f4 at the short tele range (with the Canon 70-300mm f4-5.6 IS USM, 70-200 f4 L's).
Another road could be for instance the Sigma 18-50mm f2.8 EX DC macro for the wide angle, or a UWA (Sigma 8-16mm, Tokina 11-16mm, Canon 10-22mm, Sigma 10-20mm f4-5.6) and a Canon 35mm f2 for normal prime and Canon 85mm f1.8 USM for portrait.
If you are lucky enough to have a lens that has a linear progressing CA from the center to the edge, and the offending wavelength exactly matches the red, or green, or blue channel, you can correct the CA by shrinking or expanding the offending channel. This will increase contrast and will increase "detail". This is the DPP manner, as far as I can figure out.
It is not always that simple, though.
You can also hide the CA colours, by just adjusting the offending coloured edges. This will NOT enhance contrast, and not get back the detail lost by the CA. As far as I can figure, this is what gets done by in-camera CA "correction" like for instance Nikon JPEG output does.
About the 15-85mm and its small max. aperture: genotypewriter is of course exaggerating with his "can do that with a P&S", but he does have a point. Always just having a smaller aperture available WILL just always give you that big DOF standard look, like P&S's always give you too.
Also, what I said before has to do with that.... f5-5.6 in the portrait range really just is not sensible to me. So the 50-85mm range is not great for that. And usually, when I need "tele" I need MORE than 85mm, so it does not make much sense for that either.
So a 17/18-50/55mm f2.8 lens just always makes more sense. You have f2.8 in the portrait range, and will have f4 at the short tele range (with the Canon 70-300mm f4-5.6 IS USM, 70-200 f4 L's).
Another road could be for instance the Sigma 18-50mm f2.8 EX DC macro for the wide angle, or a UWA (Sigma 8-16mm, Tokina 11-16mm, Canon 10-22mm, Sigma 10-20mm f4-5.6) and a Canon 35mm f2 for normal prime and Canon 85mm f1.8 USM for portrait.