There are three main methods by which a dSLR/mirrorless camera can be used as a webcam.
HDMI capture requires two things: that the camera can output “clean HDMI”; that is HDMI that doesn’t have camera control overlays all over it, and an HDMI capture device to turn the HDMI output from the camera into a USB webcam input to the computer. Most video-capable interchangeable lens cameras do not output clean HDMI if they are not from the last generation or two (this is written in 2020) of cameras.
Also, at the current time, purchasing an HDMI capture device or card for your computer is likely to be your biggest mountain, since most of the popular ones, like El Gato’s Camlink 4K, have been sold out/on backorder ever since the COVID-19 pandemic started.
But HDMI capture will allow for higher resolutions and even 4K.
Tethered liveview translation
The second method is using a camera’s ability to do tethered liveview over USB, and using software to translate this to look like a USB webcam input. Resolution may be limited.
Also, a lot of camera bodies can’t do this. Canon and Sony excepted, most camera manufacturers reserve this feature for higher-end prosumer models. So you’ll need to check whether your specific camera has this capability. You then need some software that can translate this liveview stream to look internally like webcam input. Typically, transforming it into Spout (Windows) or Syphon (OSX) input, and then software to make that a camera you can select from your video conferencing app.
Screen capture streaming
The third method is to use some kind of USB connection with the camera and software that can display the camera sensor’s data (typically a remote control shooting app from the manufacturer, or freeware like digicamControl) and then using OBS (Open Broadcast Software) to send that display along on a webcam stream using the OBS-virtualcam plugin (Windows) or obs-mac-virtualcam (OSX).
By camera manufacturer
Nikon has put up a webpage with instructions on HDMI capture and some commercial software solutions for liveview translation. Not sure if any of their solutions are free.
Similarly, Olympus tells you to use an HDMI capture device. But their pages do list which models have clean HDMI output.
Sony cameras, there’s nothing much on the Sony website, but enthusiasts have published how to do screencap streaming and HDMI translation).
Canon, Fuji, and Panasonic are taking advantage of their tethered liveview feature to create USB webcam capabilities with their current generation of cameras with firmware updates a Windows application to use their cameras as webcams, and are distribution free firmware/software beta builds for users.
- Canon EOS Webcam Utility, Windows 10, OSX 10.13, 10.14, and 10.15
- 1 DX II, 1DX III
- 5D Mark IV, 5DS, 5DS R
- 6D Mark II
- 7D Mark II
- 77D, 80D, 90D
- SL2, SL3
- T6, T6i, T7, T7i, T100
- M6 II, M50, M200
- R, RP,
- G5X II, G7X III, SX70 HS
- Fuji X Webcam Windows 10.
- GFX100, GFX50S, GFX50R
- X-Pro2, X-Pro3
- X-T2, X-T3, X-T4
- Panasonic Lumix Tether for Streaming, Windows 10
- DC-S1, DC-S1R, DC-S1H
My personal experience with an older camera and OSX 10.12 (Sierra)
However, if you’re an OSX shooter and your camera and OSX version are so old they aren’t on the lists above, I’ve also found Kit Farrelly’s free solution for OSX tethered liveview translation, which uses the open source Camera Live to turn the tethered liveview into a Syphon stream, and CamTwist to turn the Syphon stream into a webcam feed. I wrote about that in this answer on a Canon-specific question. Farrelly got it to work with his Fuji X-T2; I use it with a Canon 5DMkII. The resolution with my 5DMkII (confirmed with Syphon Simple Apps) is 1024×680.
I’ve also found that the $20 commercial eCamm application, iGlasses, can turn a Syphon feed into a webcam feed as well as give you basic adjustment controls/effects, if you didn’t want to go whole hog with an eCamm Live subscription, or deal with Camtwist (which hasn’t been maintained since 2013), or you needed a solution that works with FaceTime (CamTwist doesn’t).
See also: How can I set up a Canon EOS camera to be a webcam?