The Venus Laowa 9mm f/2.8 Zero-D is a fully manual focus AND manual aperture lens.
To set the aperture, you turn the narrower, knurled ring closest to the camera body. (Focus is the wider, knurled ring toward the front of the lens, of course.)
You'll see the full f-stops indicated on that narrower ring, from largest to smallest: f/2.8, 4, 5.6, 8, 11, 16 and f/22.
You will probably find "click stops" at each f-stop. Some lenses also have click stops halfway between some or all the f-stops (half stops). There are some lenses made for video that don't have click stops, but from the description of the Venus Laowa 9mm Zero-D I don't think it's that type of lens and that it will have the click stops. .
There is no electronic communication between this fully manual type of lens and the camera (the way there is with Canon's EF-M lenses... providing autofocus and aperture control, as well as IS on lenses that have it). As a result, the camera doesn't "know" what f-stop has been set or even that there is a lens mounted. So you need to read and set the f-stop on the lens itself. In addition, there is a setting in the menu to "shoot without lens" or "release shutter without lens"... something like that. You have to enable this in order to take photos with this lens. (The default setting is that the camera will prevent the shutter from firing when there is no lens mounted or when a non-electronic lens is fitted that the camera doesn't recognize.)
With this type of lens you can set exposure manually... or you can use aperture priority (Av) auto exposure. It might also be possible to set the camera to M and use Auto ISO for auto exposure. You cannot use shutter priority (Tv) or program (P) auto exposure modes. You also cannot use full auto "A+" nor any of the "Scene" modes like "sports", "landscape", "portrait" etc. In other words, since the camera cannot control the lens aperture, none of the modes where it needs to do that will work with this lens. But auto exposure modes that only change the shutter speed or the ISO can be used.
I don't have an M50, so cannot advise about using it's meter for manual exposure. Consult your user manual about how that's done. Your camera probably has "Exposure Simulation" available in the viewfinder and on the rear screen, though. and that might be helpful (especially in the viewfinder... ambient light can effect what you see on the rear screen.) With Exposure Simulation you can probably achieve a reasonably accurate exposure quickly "by eye".
Finally, it's unrelated to all the above about exposure, but manual focusing can be tricky, too. I don't know if M50 has "Focus Peaking", like my M5, but that's there to assist. You also can zoom way in on the image preview to check focus, when it's really critical. It shouldn't be too much trouble with such an ultrawide lens. Those have a lot of depth of field which makes precise focusing less critical. In fact, stop the lens down to f/8, focus to approx. ten feet and depth of field will put everything from 1.5 feet in front of you to infinity in focus!
Don't stop down too far... I would recommend avoiding f/16 and f/22, in particular. An effect called "diffraction" occurs at those really small apertures... That causes loss of fine detail in images. Besides, with so much depth of field, there's little need to ever use smaller than f/8 or maybe f/11.
I use a similar, fully manual 12mm lens on my M5. I've switched to all auto focus lenses for the rest of my kit with that camera, but ultrawides are so quick and easy to focus manually, I don't need autofocus with it. There is a large number of 3rd party, manual focus/manual aperture lenses available in EF-M mount. They are both affordable and they fill some of the gaps in the system, since there are only seven Canon EF-M lenses and six autofocus/electronic 3rd party lenses (three each from SIgma and Viltrox). Some of the 3rd party lenses are quite good!
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2), EOS M5, some other cameras, various lenses & accessories
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