Late 2015 iMac and LG Ultrafine 27": Surprise Compatibility

Discussion in 'iMac' started by Ledgem, Jul 25, 2019.

  1. Ledgem macrumors 68000

    Ledgem

    Joined:
    Jan 18, 2008
    Location:
    Hawaii, USA
    #1
    Here's one finding that I wanted to share, that I didn't find documented anywhere else on the internet.

    The basic story is that I really love the 5K display of my late 2015 27" iMac, but I've grown disillusioned with the "all in one" concept after some insects either hatched or crawled under my screen and died there (of course, within a year after my extended AppleCare expired), leaving me with an annoyance despite the fact that this computer still has at least another two years of life left in it. I plan to transition to a Mac mini in the future, and in preparation, came across a nice deal on a LG Ultrafine 27" 5K monitor. Apple's own support page for the Ultrafine states that only iMacs from 2017 and newer can use the Ultrafine at its native resolution; iMacs from 2015 (and 2014) are said to only be able to drive it at a 4K resolution. Fine by me, as this would just be a secondary display.

    I bought the Thunderbolt 3 to Thunderbolt 2 adapter and a Thunderbolt cable, and was shocked to find an image that looked just as sharp and life-like as my iMac's display (albeit with a slightly cooler color cast). Windows sizes and fonts all looked the same, as well. If this was what 4K scaling looked like, then who really cared that it wasn't true 5K? But a bit of digging revealed that it probably looked that good because it really was being driven at 5K:
    Screen Shot 2019-07-25 at 8.14.33 AM.png
    The System Information pane seemed to support this:

    Displays:
    iMac:
    Display Type: Built-In Retina LCD
    Resolution: 5120 x 2880 Retina
    Framebuffer Depth: 30-Bit Color (ARGB2101010)
    Main Display: Yes
    Mirror: Off
    Online: Yes
    Rotation: Supported
    Automatically Adjust Brightness: No
    LG UltraFine:
    Resolution: 5120 x 2880 (5K/UHD+ - Ultra High Definition Plus)
    UI Looks like: 2560 x 1440
    Framebuffer Depth: 30-Bit Color (ARGB2101010)
    Display Serial Number: (removed for public posting)
    Mirror: Off
    Online: Yes
    Rotation: Supported
    Automatically Adjust Brightness: No
    Connection Type: DisplayPort

    Refresh rate isn't listed in any of these and Apple has made it very difficult to see what the refresh rate is these days, but mouse and window dragging movement is entirely smooth; I'd be surprised if it weren't running at 60 Hz.

    While it's possible that Apple made a mistake with their documentation, I'm guessing it was more a matter of simplification. I chose the maximum upgrades for the CPU and graphics chip when I ordered my iMac, and then maxed out the RAM on my own. The CPU and RAM shouldn't impact this, but the graphics chip would. My guess would be that the other graphics chip options for the late 2015 iMac would be limited to a 4K resolution. Yet Apple's support document would become needlessly complicated if they wrote about what the exceptions were; easier to say that all late 2015 iMacs can't drive it to avoid confusion. Either that, or they never actually verified that this configuration would work.

    It's a pleasant surprise. The only downside is that now I might get used to working with two 27" 5K displays, and then when the time comes to move away from my iMac I'll find myself looking to purchase another Ultrafine...

    (note to anyone else looking to try this: the Ultrafine comes with a nice, long Thunderbolt 3 cable, but Apple's Thunderbolt adapter is a Thunderbolt 2 to Thunderbolt 3 adapter that requires you purchase a Thunderbolt 2 (or 1, they're the same) cable. Use the 2 meter cables; the 0.5 meter ones aren't long enough to have the monitor and your iMac side-by-side, unless they are facing away from each other. Unfortunately the Thunderbolt ports on both displays are on the left side, so this applies whether you would plan to place the Ultrafine to the left or right of your iMac.)
     
  2. whosthis macrumors member

    Joined:
    Aug 21, 2008
    #2
    Thanks for sharing. Keep the TB3 cable, the good ones are really expensive, and you can probably use it in the future.

    Are you using it as the main screen now? You might even use the mirroring option and dim the iMac down (or stow it away under the table) - but I guess 2 screens is just too tempting.
     
  3. Ledgem thread starter macrumors 68000

    Ledgem

    Joined:
    Jan 18, 2008
    Location:
    Hawaii, USA
    #3
    I'm continuing to use the iMac display as my primary screen at this time. I got used to the insects a lot faster than I thought I would, and while it still bothers me, it's really only in certain use cases that it comes up. I figure I might as well save wear-and-tear on the Ultrafine, as well. And yes, if you have two screens, the temptation to use the dual-monitor setup is too good - particularly as I do use programs that can make use of dual displays.

    That leads to one sub-optimal reveal about the Ultrafine specifically, when it's not being used as a primary display. I don't want to just have a static image burning in on it when I don't need two displays, but the Ultrafine doesn't have any physical hardware buttons to power it off. While there are programs for the Mac that can disable other displays and I had read online that doing so would cause the monitor to power down, even with those programs the Ultrafine continues to be powered on, just showing a black screen when disabled. For now, I'm connecting and disconnecting the display's Thunderbolt input depending on whether I need the second screen or not. Others on the internet have taken to using remote power switches to forcefully power down the display when they don't need it. (The display properly powers down when the Mac's display is off.) I knew about the lack of physical hardware buttons going in, but I guess I hadn't thought about it much, particularly as this is my first external monitor completely lacking in buttons and I believed the reports about it shutting off when disabled.
     
  4. whosthis macrumors member

    Joined:
    Aug 21, 2008
    #4
    Yes, "disabling" a monitor completely is really a lacking feature.

    For example, I have a 2nd screen hooked up, but want to use it only rarely. It has a power "button" on the front and a real switch on the back. Only the switch will make the "disappear" from the system. Especially when hooked up to another machine at the same time, this is a rather poor experience. I do understand that this is not what > 90% of the people would usually want.

    What software would disable the screen? I might give it a try here.
     
  5. mikehalloran macrumors 68000

    Joined:
    Oct 14, 2018
    Location:
    The Sillie Con Valley
    #5
    Does the Ultrafine get its power from the TB cable or a separate AC main?
     
  6. chrfr macrumors 604

    Joined:
    Jul 11, 2009
    #6
    It has its own power cord that goes to a wall outlet.
     
  7. mikehalloran macrumors 68000

    Joined:
    Oct 14, 2018
    Location:
    The Sillie Con Valley
    #7
    Thanks for that.

    The power button issue has an easy solution. A power switch can be installed in line with the cable. A power strip is easy and most of us have them lying about but you can get 1–2 socket units, too, as well as short cables from 6"–18".

    Inelegant? ugly? Yes but practical and cheap.

    Also, something like one if these can be plugged into the end of a short extension cord.
    https://www.amazon.com/Belkin-Conse...th+switch&qid=1564092329&s=electronics&sr=1-4

    Anyway, it's an easy problem to solve.
     
  8. Ledgem thread starter macrumors 68000

    Ledgem

    Joined:
    Jan 18, 2008
    Location:
    Hawaii, USA
    #8
    Most people talked about SwitchResX. It has a free ten-day trial with no features withheld, so you can try it for yourself pretty easily and see if it works. It's $16 (or 16 Euros, depending on your location), which seems like a decent asking price if it works for you.
     
  9. whosthis macrumors member

    Joined:
    Aug 21, 2008
    #9
    Cool, I used this in the past and have a license already anyway.
     

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8 July 25, 2019