I didn't exactly buy the Voigtlander 40mm f1.4 lens on a whim. I've been using the Sigma 45mm f2.8 lenses for several years now and I like that focal length niche between 35mm and 50mm lenses. The 45mm is good but the slightly wider 40mm is great. I know. There are some among you who can shoot anything with a 20mm lens, pre-visualize exactly the crop you're going to make weeks from now in post, and happily proceed. But the rest of us don't do that. We like to be flexible but we're even more comfortable if we know where the edges are and we calibrate our compositions to those restraints.
I chose the 40mm V. lens because it covers full frame, is fast enough for low light work (night scenes on city streets) and it features manual focusing. One of the bigger advantages is the small size of the lens.
But my most compelling reason for buying and packing the lens was my research into the "look" of the images made with this lens by various photographers who share their images on the web. The lens is sharp in the center even when used at f1.4. The lens has vignetting (which I like) but it's not so much vignetting that it can't be corrected in post without obvious corner artifacts. The standout optical characteristic is the way it handles colors. It's neutral in contrast but the colors it creates are more saturated; more color rich than the other 40-45mm competitors. And that's something I like.
I know you can add saturation in post but the rendering is different if a certain level of saturation and clear discrimination between colors is built into the optical formula.
This is the lens I took with me to Vancouver and, for the most part, I'm very happy with my choice. It was just the right package for casual shooting on vacation. The only thing I would want to change would be an assurance that the lens was water resistant. I didn't have any issues with the lens but it would be comforting to know that steps had been taken in manufacturing to keep moisture out of the system. But that's all psychological; I'm pretty sure.
In normal practice I never use a "protection" filter on the front of my lenses but in this instance I decided to spring for a B&W filter to use on the front. Just an extra barrier between rain drops, snow and the front element. I'd rather keep wiping drops off the front of a replaceable filter than off the optical element.
Several people have commented that the images from my vacation trip look different than the ones I usually post. I would have to say that a large part of the difference in "look" comes from the characteristics of the lens. The rest come from the use of the lens on a different camera. It's a good combination with the Lumix S5. The only real difference I can think of in the whole shooting process was to consistently shoot cooler (more blue) color corrections than I usually do. And I added fewer changes in post processing --- letting the camera and the lens express themselves more transparently.
I think that because of the influx of so many technical people into the field of digital photography over the last twenty some years there is a belief in the binary nature of everything. This would include that, other than sharpness, all lenses of a particular focal length are interchangeable. Or, if there are big differences between the way two lenses render an image then the extension of the technical-oriented thought process is that the differences can be squashed down and homogenized in post processing.
The follow on thought to that is the assumption that there is a universal color/contrast/D-range look that should be the standard for all images. Which is absurd.
I like the 40mm V. lens not for any particular thing it does brilliantly but for its faults and peccadillos. I love the vignetting. I love the soft flare over small areas of a sharp image when shooting into small light sources. I like image edges that aren't samurai sword sharp. In short, sometimes I like a lens more for its "faults" (which aren't faults but are instead signatures) than I like most lenses for their purported perfection.
There are many cases where high performance and a highly accurate documentation are necessary. An example would be commercial still life photographs of small objects which look best with high sharpness and detail. A "clinical" macro lens would be the choice for those situations... But there are many times when a less accurate lens provides the differentiation from the typical rendering which actually makes the resulting photograph more interesting. More intriguing. Less a slavish documentation.
When I shoot with a lens like the 40mm I know I'm not getting a direct and complete representation of the object being photographed. But I am getting an interpretation of the object and that interpretation is something I understand will happen when I choose a certain lens.
It's part of the reason LensBaby products endure. Or why some older Canon FD lenses are in high demand. It's because of their personalities that people buy them. If they were craving accuracy overall they'd probably choose a Zeiss Otus lens instead.
Clinical versus Personality. There's a place for both and it's dictated by the intended final use of the image.