A rule of thumb – lenses display their flaws at their operational extremes
- widest and narrowest apertures
- shortest and longest zoom ranges (for zoom lenses)
- very high contrast shots
- sometimes – extreme focus points (as close as possible and at infinity)
- zooms normally show more flaws than equivalent primes

Often, just avoiding those extremes (when possible) will dramatically reduce CA, improve sharpness, improve focus, and reduce distortions (barrel and pincushion).

Pro lenses generally reduce these problems up front (better design and materials) and have a wider operational range.
Example:
A. 70-300mm f4-5.6 “Weekend Warrior” model by Gizmo Company – max aperture at 300 is f5.6 – stop it down a couple of stops to improve sharpness and you’re shooting at f8 which may require a lot of light and still may be a little soft and show some distortion. Cost $189.50.
B. 70-200mm f2.8 “Super Big and Heavy” model by Professional Glass Inc. May show fewer flaws “wide open” than the previous model did stopped down. If shot “stopped down” at f4 is still much faster than the consumer zoom and probably sharper too. Cost: $1200.
C. 200mm f4 Prime “Nicely Done” model by Gizmo Company shot at f4 may be sharper and show less distortions and CA than either of the other two. Cost: $650.

The names have been made up to protect the innocent – because the names are irrelevant. There are always exceptions in the performance / cost curve – some of them perform better than their specs and price suggest, some of them much worse. The discussions of (for example) the “best” consumer 70-300mm zoom are carried on for pages and pages in forums across the web.

In general, however you can fill in the names of your favorite companies above (Nikon, Canon, Sigma, Tokina, Tamron, Quantaray, Minolta, Zeiss) and you would find the above scenario is repeated across all lens lines.

The key, my friend, is to learn how to shoot in such a way (when conditions and subject matter permit) as to reduce the inherent flaws in any camera / lens combination. That means that shooting with a $189 lens requires compromises and under certain conditions, shooting is impossible.

Sometimes it requires a better setup to get the shot!

Stop down the lens a stop or two and get away from the 300mm end of the focal length, and you will probably reduce the CA problems (and improve the sharpness and distortions also).