When it comes to compact M-mount lenses its hard to compete with Voigtlander's offerings. They all come with a high quality build, fast apertures and small compact sizes. When shooting mirrorless cameras, part of the joy is the ability to more easily shoot manual lenses such as the ones offered by Voigtlander, as well as other legacy lenses. When looking at M-mount 35mm lenses, 2 of the most sought after are the Voigtlander 35mm f1.4 Nokton and the Voigtlander 40mm f1.4 Nokton. Both offer a really fast aperture, short focus throws with smooth fluid movements and a compact size. Price-wise, the 40mm is usually $150-$200 cheaper than the 35mm version, so we examined the wide open properties of both lenses to see if performance was a reason why.
The 35mm f1.4 is a "standard" focal length. Often sought after for general purpose shooting, street photography, and events. The 35mm focal length is often considered a perfect balance of "not too wide" and "not too narrow" and can be used for portraits especially environmental portraits and fashion/editorial work.
The odd 40mm focal length of the Nokton, is uncommon. Though only 5mm difference stands between the 35mm and the 40mm, we've found that the perspective it provides more closely resembles a 50mm lens than a wider 35mm lens. That being said, there's no confusing this focal length for a mild-telephoto when used on full-frame camera. On an APS-C censored camera such as a Sony A6500, Fujifilm X-Pro2 or Fujifilm XT-2, the 40mm lens provides a unique perspective much more interesting then a 35mm lens on the same body would with its 60mm Vs. 50mm equivalent on full frame.
Size wise the 40mm is slightly taller, very slightly so. The 40mm is on the left and the 35mm on the right. As for weight, the 40mm weighs 197 gram and the 35mm weighs 198 grams, so again very similar.
Wide-open performance. While both lenses showed purple fringing in the high contrast areas of the target, the more expensive 35mm lens showed more of it than the cheaper 40mm Nokton. Wide-open sharpness in the center was just about even. With perhaps the slight (very slight) nod to the 40mm lens. You can see more "swirl" in the out of focus areas of the 35mm lens however; adding to its character.
Voigtlander 35mm f1.4 at f1.4 (wide-open)
Voigtlander 40mm f1.4 at f1.4 (wide open)
One clear distinction between both lenses is the depth of field (DOF) difference. The 40mm clearly shows less DOF, with smoother bokeh balls, less pronounced onion-ringing and more pleasant look, to me anyway.
Voigtlander 35mm f1.4 at f1.4, corner crop
Voigtlander 40mm f1.4 at f1.4, corner crop
Now lets look at both stopped-down to f2...
Voigtlander 35mm f1.4 at f2
Voigtlander 40mm f1.4 at f2
Voigtlander 35mm f1.4 at f2
Again we see a similar bokeh performance. Both do get hexagonal but the 40mm maintains smoother bokeh overall, if only marginally. Of course the extra 5mm of reach are to blame for this, so nothing earth shattering but it is noticeable. What is worth considering is the price difference. At $200 difference, unless you are mounting the lens on a Leica or other cameras without the 40mm frame lines, its hard not to recommend or suggest for consideration, the cheaper, better corrected and "better" bokeh delivery of the 40mm Nokton.
PS:
The 40mm Nokton, though arguably better performing than the 35mm f1.4 wide-open, it does more closely resemble a 50mm lens. So would a better comparison have been made against Voigtlander's own 50mm f1.5 Nokton? But that 50mm Nokton lens is twice the price, larger and heavier. Is the 40mm really in a class all its own? And if it is, perhaps its a classic in the making.