What is a "professional" lens?

[Loupey]

I'd say it's just simply the most expensive model in any series - whether it's a zoom range or specific prime focal length.

The build quality is the most noticeable difference IMO. The image quality improvement can sometimes be very small. Many "mid-level" lenses are very good already and one has to look quite hard sometimes to see the difference.

It's not sheer image quality. My 28mm, 50mm, and 85mm non-L primes are much sharper than the "L" zooms which cover these focal lengths. I know, zooms and primes are not in the same class - but I think you get my drift.

I like to use the sunscreen analogy: Most people think they have to buy SPF 45 over the SPF 15 stuff - in reality, the additional protection they are paying extra for is only 1~2%. So in terms of photography, the finest is available if you want to pay for it or if you are paid to do it. But whether you can utilize it to its full potential, well that's up to you

[AgingEyes]

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The build quality is the most noticeable difference IMO. The image quality improvement can sometimes be very small. Many "mid-level" lenses are very good already and one has to look quite hard sometimes to see the difference.

I agree. But, you know about my eyes ...

My 28mm, 50mm, and 85mm non-L primes are much sharper than the "L" zooms which cover these focal lengths. I know, zooms and primes are not in the same class - but I think you get my drift.

Nikon 70-200 f2.8 VR may be the exception though. Thom Hogan has concluded that at 85mm, both the primes 85 f1.4 and 85 f1.8 are not as good as the zoom. Then again, I believe the zoom is the newer lens of them all.

BTW, I'm reading this thread because of Frog's answer on another thread

[Liz]

Great thread. Thanks Frog.

I won't add to the original "what is" question in my reply since others have covered it all. However, I will add that when I invested in my first "L" lens - the Canon 17-40L f/4 I was amazed at the image quality, build, etc. The results I got with that lens were incredible. The first time I used it I was literally taken back by the quality of the images right out of the camera. It was my all time favorite lens (along with the 24-105L IS).

I don't have a lot of time for photography, so I try to get the best results I can right out of the camera with less time spent on the computer. I must say with the 17-40 and 24-105L IS lens there was very little post processing that had to be done.

Unfortunately I ended up selling both of these lenses after an accident that gave me back/neck problems and I couldn't carry heavy equipment around. My 50mm/f1.4 does a fantastic job though - very close to the "pro" in IQ.

Liz

[Loupey]

Rethinking this a bit, for me the biggest difference is how much a lens has to be stopped down in order to achieve "useful" sharpness/contrast. With some lenses, I am comfortable shooting stopped down just a half-stop or even wide open under certain cases. With others, it takes a full 2+ stops to reach it.

My 28mm, 50mm, and 85mm non-L primes are much sharper than the "L" zooms which cover these focal lengths. I know, zooms and primes are not in the same class - but I think you get my drift.

Since I wrote that, I bought the 24-105mm Canon and was blown away by it's IQ. The 28mm f/1.8, 50mm f/1.4 & f/1.8, and 85mm f/1.8 mentioned above couldn't compare to it unless stopped down to about the f/4 anyway.

So, for me, usefulness at ALL apertures would be the qualifier.