Having just got my new 2020 27″ iMac set up with my old Apple 30″ Cinema Display connected as a second monitor – no trivial task – I thought I should leave the instructions here for anyone else who wants to do the same.
Here’s what you need:
• A free USB-C port on the Mac.
• A USB-C to Mini Display Port adaptor (around $15). From what I’ve read, this needs to be able to accept input from an active (externally powered) DVI adaptor (evidently some don’t).
• A Mini Display Port to active dual-link DVI adaptor (over $100). This is the most crucial part. As well as the two connectors, it has a USB-A plug that is necesssary to supply power for the active link.
• Your trusty old Apple Cinema Display.
- Plug the first adaptor into your Mac.
- Plug the second adaptor into the first; plug the USB-A into the Mac.
- Plug the Cinema Display’s DVI plug into the DVI port.
- Power up.
- The Cinema Display will light up in low resolution.
- Open System Preferences: Displays.
- On the panel for the Cinema Display, find “Resolution”. Hold down the Option key and click on Scaled. Like magic, extra resolutions appear. Select 2500 × 1600. The screens will go black and then come up again.
I found both connectors on Amazon: “Silebing09” brand and “StarTech” brand (MDP2DVID2).
I am now a happy camper.