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LG UltraFine 5K & Mac Pro (Late 2013): 5K resolution showing in display preferences - is it 30Hz?

Y

yaosiang

macrumors member
Original poster
Jul 3, 2010
57
49
Hello,

My local Apple Store has LG UltraFine 5K monitor hooked to a Mac Pro (Late 2013) via TB3 to TB2 adapter running at 5120 x 2880 resolution.

Based on my understanding from this forum, it is impossible to run 5K resolution via single TB2 output due to limited bandwidth of DisplayPort 1.2. Usually, 2 x TB2 outputs are required to drive a display at 5K resolution (such as the Dell UP2715K). According to https://support.apple.com/en-gb/HT207448, the Mac Pro (Late 2013) only supports maximum of 4K resolution at 60Hz.

So could someone please explain why am I seeing 5120 x 2880 in display preferences? Is it possible that the Mac Pro is able to support 5120 x 2880 at 30Hz on the LG UltraFine 5K monitor?

Cropped screenshot:
macpro.jpg



Full size screenshots taken from the Mac Pro in Apple Store:

First test:
5120 x 2880 (File size: 28.1MB)
https://dl.dropbox.com/s/m3eo5swfczw6uuz/Screen Shot 2017-02-25 at 18.51.22.png

Second test:
Default for display / 2560 x 1440 (File size: 21.1MB), please note screenshot size is 5120 x 2880 pixels
https://dl.dropbox.com/s/6ipaeh4k9ykl462/Screen Shot 2017-02-25 at 18.50.50.png

Third test:
3840 x 2160 (File size: 56.2MB), please note screenshot size is 7680 x 4320 pixels
https://dl.dropbox.com/s/e35aoer2xupc27g/Screen Shot 2017-02-25 at 18.43.54.png

Also, how do I check the refresh rate for LG UltraFine 5K? The monitor itself does not have any buttons!
 
If I'd had to guess, it might be the easiest way: 30Hz.
Why else would they hide the refresh rate?

I'm pretty amazed that there's so little discussion about this.
Have die-hard mac hardware fans died?
Or moved to other boards?

Maybe posting this to macpro section?
 
Last edited:
As I remember there are documented hacks for getting 5K monitor to work on Mac Pro. You have to connect one TB cable to each of the two system busses.
 
My bad. I was thinking of how folks has connected Mac Pro to 5K monitors using dual TB2 connections doing MST.
 
Short version:
Although Mac OS X is reporting the monitor to be running at 5120 x 2880, according to SwitchResX the actual output to the display (tested on 2015 rMBP) is 4096 x 2304 at 60Hz.

Long version:
I went back to Apple Store to test the LG UltraFine 5K monitor with a Mid 2015 MacBook Pro 15" with Radeon R9 M370X dGPU. The results are exactly the same as the tests I did on Mac Pro (Late 2013), except the colour output was 8-bit on the rMBP as opposed to 10-bit on the Mac Pro. The resolution was 5120 x 2880 under Display Preferences and System Report. The image size of screenshots are also 5K resolution.

Cropped screenshot from rMBP:
mbp5kdisplay.png


However, interestingly SwitchResX is showing that the resolution output to the monitor is 4096 x 2304 at 60Hz scaled to 5120 x 2880. I guess that confirmed the theory that a single TB2 link can only support 4K max and we cannot rely on System Report to show the actual output resolution from the GPU.

switchresx2.png

I did not have the chance to test if I could create a custom resolution in SwitchResX to drive the display at 5120 x 2880 30Hz. Anyone would like to guess if that will work?
 
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So with the above in mind, would you say the LG is a better display @4K with an older MacBook (2015) than using an old Thunderbolt 27"?
 
ljt said:
So with the above in mind, would you say the LG is a better display @4K with an older MacBook (2015) than using an old Thunderbolt 27"?
Click to expand...

Sorry to revive this old thread, but I was wondering the same thing about the quality if running older Macs at 4K on this monitor. Any experienced owners care to chime in, please?
 
^^hoping to revive this old thread as well - need a display and hoping to get an LG 5k to future proof even tho I still have an old 2013 MacBook Pro Retina, w/ NVIDIA GeForce GT 750M 2048 MB (for the moment). I would def use it with my next machine (prob within the year) but wondering if it would work with this one and if so, what the experience is of the scaled resolution?
 
Wondering the s
mysterioso said:
^^hoping to revive this old thread as well - need a display and hoping to get an LG 5k to future proof even tho I still have an old 2013 MacBook Pro Retina, w/ NVIDIA GeForce GT 750M 2048 MB (for the moment). I would def use it with my next machine (prob within the year) but wondering if it would work with this one and if so, what the experience is of the scaled resolution?
Click to expand...
Wondering the same!

Has anyone tried hooking up 2013 MacBook Pro Retina, w/ NVIDIA GeForce GT 750M 2048 MB with LG UltraFine 5K?
 
Oh, I totally missed that part. With reagrads to the resolution, would that mean a lower ppi?
 
3840x2160 is lower effective ppi. The Mac can do retina scaling and then the monitor scales to 5K so some find it unusable for graphics. I find it great for office and web apps. Also some can't tolerate 30Hz and others are fine with it.
 
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