I realize that you can get sharp pictures if the soft focus feature is set to "zero." Is there a way for the user to lock this in place so that it can't move off of that setting inadvertently?
don't worry about that, there is no way this can happen
What are your impressions of the lens overall? What I have found out so far from searching the board is that it is sharp, though not "L" sharp, when it's not in soft focus mode. Also, it's not that smooth in focusing (lacking an USM), but will get you there. It's shorter, half the weight, and less than a third of the price of the 135/2L.
I'm very happy with this lens, and, by the way, soft focus is a nice feature:
https://photography-on-the.net …topic.php?p=225321#225321
But, I'm also aware of this lens weak sides.
I think this lens is the least expensive telephoto (100+) that gives you f/2.8. That's was the main reason I bought it. I actually like the soft focus feature too. I'm still sure it's not that easily reproduced in photoshop, however, I could not prove it here (there was a thread regarding soft focus about a month ago).
If you are looking for ultimate sharpness, you can probably find something better for not much more money. 85 f/1.8, for example.
Sometime ago I borrowed 75-300 III USM lens from a friend to compare with 135. I put 75-300 at 135mm and set apereture to 5.6 on both lenses. I could not see much difference. I think that 75-300 was even better in terms of the sharpness off center. But, of course, one cannot set 75-300 to f/2.8
May be I have a "soft" copy, or may be my friend has a very good copy of 75-300, I don't know. However, photodo.com MTFs confirm what I see in practice.
Anyway, if you decide to buy this lens, make sure you buy it for the right reason.