External 4K monitor questions

[jmacru]

I recently tried, and failed to setup a 27" (2560x1440) external monitor with my 2018 13" MacBook Pro. The text looked awful, and despite trying various "fixes" nothing really improved it, and I ended up returning it.

More research has indicated I need a 4k monitor, which I then have to run at a reduced resolution, to make it act like the retina display. I'm trying to get an idea of how this will actually work, before I commit to another purchase.

What will the usable resolution be the equivelant of (so I can get an idea of how much I'll be able to fit on the screen)?

Also, if I do the above, and run in "retina mode", will I be able to use the scaling options you get for the built in display to fine tune it (e.g. 'Larger Text', 'Default', 'More Space').

 

[njvm]

There are lots of threads on this site on this subject. For instance:

Scaling 1440p in a 4k monitor compare with NATIVE 1440p monitor?

Hi guys, I'm looking to get a suitable external monitor for my MacBook Pro 15' 2019. I m thinking to 2 option: first is my favor the LG Ultrafine 4k 24inch, second is a 24-25 inch at 2560-1440 resolution (there are plenty of those in the market). After doing some research, I found that if using...

forums.macrumors.com

 

[joevt]

The "Larger Text", "More Space" options just change the framebuffer size using different scaled modes.

Retina modes draw text and objects twice as tall and wide as low resolution modes. You can see all retina modes by holding the Option key and selecting "Scaled" in the Displays preferences panel. Then enable "Show low resolution modes" to see the low resolution modes. It also lets you change the Refresh Rate.

You can make any retina mode by adding a scaled mode with the desired resolution. A "Looks like 2560x1440" Retina mode (also called HiDPI mode) draws into a scaled mode that is 5120x2880. The GPU scales that to fit the display - 3840x2160 in the case of a 4K display.

The native retina mode for a 4K display is "Looks like 1920x1080". This mode requires no scaling to a 4K display because the framebuffer size matches the size of the 4K display - 3840x2160.

You can do "Looks like 3008x1692" mode which has the same area as the native retina mode for an Apple Pro Display XDR. This mode might be ok on a 27" display but it would be better on a 30" display - I guess it depends on how close you are to the display.

You could do a "Looks like 3840x2160" mode but it wouldn't look much different than the normal 3840x2160 mode. This retina mode uses a 8K frame buffer.

I recommend using SwitchResX for creating and selecting the scaled modes you want (in case they are not created automatically).

 

[Fishrrman]

You need a 4k display running in HiDPI mode (which mimics "retina mode" on an external display).

The actual image will "look like" 1080p, but each "pixel" will actually use -4- pixels, resulting in an image that is much sharper "to the eye".

You'll also need a good connecting cable. Be careful choosing one (and read user reviews if any are posted) -- they're not all the same.

 

[Amethyst1]

What will the usable resolution be the equivelant of (so I can get an idea of how much I'll be able to fit on the screen)?

I went from a 27" 2560×1440 to a 23.8" "4K" which I run scaled to 2304×1296. This means the resulting (simulated) pixel density is very similar across the two setups, i.e. UI elements and text are just about the same size. I found 1920×1080 (the default) to be useless because everything is way too big and I don't have enough screen estate; 2560×1440 is just a tad too small on 23.8" for my eyes.