It's always nice to have lenses that are sharp when used wide open. There are times when you want the backgrounds to blur away...

 

One of the things I always liked when using a 180mm f4.0 Zeiss lens on a square format, film Hasselblad was the ability to photograph with it wide open and still get high sharpness in the areas that were supposed to be in focus. With medium format even f5.6 at that focal length seemed to give me very narrow depth of focus. When I choose lenses for my 35mm sized digital cameras I find that the better corrected the lens is at its widest aperture the nicer my portraits look; at least to me. 

I've gone down the path of trying very inexpensive, fast lenses only to be disappointed most of the time the time. One of my favorite portrait lenses right now is the Voigtlander 50mm f2.0 APO-Lanthar. It's an exquisitely sharp lens at its widest aperture. I know, it's only a 50mm so it doesn't really fall into the traditional focal length range for portraiture. That's why I sometimes use it on an SL2 camera which is 47 megapixels at full frame and still 22 megapixels when using the APS-C crop. When I use it in that fashion it's great for classic studio portraits. 

The lens costs about $1,000 new but it's better than my Carl Zeiss ZF.2 50mm f1.4 or the Voigtlander 58mm f1.4 when either of those lenses is used at f2.0. And when used wide open at f1.4 neither of those older lenses is sharp enough across enough of the frame to get the sharp/soft look I want in a portrait.

Could be that a 50mm APO when used on an APS-C camera or on a camera with a crop that equals 75mm is a glorious sweet spot for making convincing portraits of people. 

I do, however, miss the longer lenses on a big, big, fat medium format film frame. We gave up too much when we all moved over to digital. It just wasn't ready yet...

But in today's imaging environment fast, sharp, well corrected APO lenses get us back to the quality levels we appreciated. Finally.