Lens variations

Joe Moche wrote:

A common theme on many of these forums involves folks who argue over the sharpness of a particular lens. The argument often ends with "You got a bad sample. Send it back." Honestly, there seem to be an awful lot of "bad samples" floating around out there.

If they are offering you their particular lens, then that could be useful information.

I find discounted lenses are often poorer samples.

Is the lens manufacturing process really so loose that a high number of bad samples would be produced?

Sometimes.

I've tried multiple copies of several lenses. Some are more consistent, some vary a lot.

Are bad samples just an aberration, or is there a range of sharpness (from great to poor) that affects all lenses?

Some manufacturer's seem to have become much more consistent recently. But every lens is somewhat imperfect. But just like there are bad copies, there are also exceptionally good copies, and some variations offer performance tradeoffs for specific uses.

Do lens manufacturers test a lens before boxing it up, and is there some minimum level of performance that renders the lens "good enough?"

Sometimes. Probably.

Finally, how can one know if a newly-purchased lens is a bad sample, other than by making a totally subjective assessment by comparing results to results claimed by others?

I test every lens when I get them.

I have neither the time, skill, or desire to run lab tests on every lens I buy, and if a lens doesn't meet my expectations, I have no problem sending it back. That said, I see no reason to settle for "bad copy" when a better copy can be had for the same price. Thoughts?

One could spend an unlimited amount of time seeking better copies.

A bought a used Sony E 16mm F2.8 and wasn't particularly impressed with it, so I bought two more copies of it. Both were worse than the first one.

I bought a Samyang AF 24mm F2.8 FE. Three subsequent copies were all a little better than the previous one. The last one was significantly better. About the same time I sent a misaligned Tamron 24mm F2.8 in under warranty. It came back the same. Marc Alhadeff rates the Tamron as outstanding for sharpness and the Samyang as average.