Bad lens copy

[AlQ]

In reading through a number of forums and reviews on lenses, I see that it is possible to get a bad copy of a lens.

How can you determine whether the lens is a bad copy as opposed to just bad technique shooting?.....what are some definite characteristics to look for?

thanks!

[bono]

Indeed, a lot of bad copys are not as bad as people state. Quite a lot of "bad" lenses are just used the wrong way.

But, as you note, there are also real bad lenses. One example is the Sony SAL-1870. There are some good copys around but most of them are not very good.

Bad lenses usually tend to be not very sharp and don't get sharp even if you stop down the lens to say f/11. The weakest point of a lens the corners. Even expensive lenses are not as sharp in an corner as in the centre of the picture. But the centre is usually very sharp. With a bad lens you will find everything lacking sharpness. Some lenses also tend to have a bad colour reproduction - you will find the images flat and rather dull.

So if you are shooting a series of panoramic pictures in bright sunlight and no one is sharp you are likely to have a bad performing lens.

[Aegea]

Every lens I get, I make a series of test chart shots. Comparison with other lenses (even different focal lengths and manufacturers) gives a pretty good idea of whether a particular copy is bad.