У всех этих блинчиков очень низкое разрешение на открытой, особенно по краям кадра (по сравнению с фиксами S-линии и даже зумами 24-70/4 и 14-30/4 на диафрагме 4), а диафрагма 2.8 - не далеко ушла от диафрагмы 4, то есть особых преимуществ не даст. Проще в поездках иметь один небольшой зеткин зум, остальное сделает стаб. Если уж хотеть радикальных изменений в картинке и светосилы, то нужно брать полноценный фикс, не блинчик.
Например, разрешение 28/2.8
Для сравнения 30 мм на 14-30/4 (не самая сильная сторона этого зума)
И 24 мм на 24-70/4:
И сам фикс 24/1.8
К тому же блинчики имеют сильную кривизну поля. Вот что пишет Мансуров о 40/2:
The Nikon Z 40mm f/2 has pronounced field curvature, meaning that the “plane” of sharpest focus is curved rather than flat. Field curvature is responsible for the odd-seeming result at f/4 in the Imatest graph above, where midframe sharpness appears worse than corner sharpness. In reality, this loss of midframe sharpness is due to out-of-focus blur instead of blur from other lens aberrations.
To help visualize things, here’s our measurement of the lens’s mustache-type field curvature at f/4:
Field curvature is present at other apertures, too, but it affects the Imatest graph most noticeably at f/4 in our tests. In practice, you may not care too much about field curvature as a photographer; test charts exaggerate the issue relative to most three-dimensional subjects.
That said, it still depends on your subject. If you’re shooting a landscape at an overlook where everything is approximately at infinity focus, field curvature can cause a significant loss in sharpness in parts of your photo. On the other hand, if you’re photographing something like close-up scenes with a shallow depth of field, the issue may not be relevant at all.
И еще у него есть шифт-фокус:
As for focus shift, the Z 40mm f/2 has quite a bit. If you focus at f/2, then stop down to something like f/2.8 or f/4, your focus point will migrate behind your subject. With the Nikon Z 40mm f/2, it’s important to stop down to your desired aperture first, then focus, if you want to eliminate the problem.
Note that Nikon Z cameras are programmed to focus at your selected aperture, so long as you’re using f/5.6 or wider. This effectively prevents the issue of focus shift, so long as you always stop down your lens before focusing.
https://photographylife.com/reviews/nikon-z-40mm-f-2/2
Сравнение по разрешению 40/2 с 50/1.8 без слез смотреть нельзя:
Боке у него - тоже скверное.