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I have two Macs both running Lion:

  1. iMac (early 2009, iMac9,1 with NVIDIA GeForce GT 120)

  2. MacBook Air (Early 2011, first of the new shape 11.6")

I often screen share using the Macbook Air as the client, and presenting the screen from my iMac onto it. When this happens the original iMac screen resolution is used and scaled down to fit into the lower resolution on the Macbook Air.

The iMac resolution native resolution is 1900x1200 (16:10), so when scaled down to Airs 1366x768 (16:9) it looks bad and doesn't fill the screen (even after using "full screen").

When I am in though, I can change the resolution, and have elected to put the display preferences menu bar item in to allow me to change quickly.

If I screen share using the normal physical display, I get the following choice of screen resolutions:

Physical Resolutions

If I select to use the virtual display instead my choice of available screen resolutions changes to the following:

Native Resolutions

Oddly these are "extra" resolutions, but none of the available choices match the 16:9 aspect ratio of the Air, or equate to any of the supported 16:10 ratio resolutions of the Air, I only get options for the 4:3 aspect ratio.

Macbook Air Supported resolutions:

1366x768 (native), 1344x756 and 1280x720 pixels at 16:9 aspect ratio

1152x720 and 1024x640 pixels at 16:10 aspect ratio

1024x768 and 800x600 pixels at 4:3 aspect ratio

I want to avoid scaling wherever possible, and use one of the 16:9 ratios that my Air supports to get full screen non scaled viewing. I can get native vertical with horizontal borders at 1024x768, or I can get close to full screen after scaling with slim borders by using 1680x1050, but neither of these are ideal.

Is there any way to set my iMac to use these resolutions when I am connected via Screen Sharing? I know the root cause is a fundamental mismatch in aspect ratios, but surely the iMac can support a 16:9 external display, so why not for a virtual display?

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Until you find a way to trick the resolution - do make note of the Turn Scaling Off ⌥⌘S and Full Screen modes in the View menu –  bmike Aug 10 '11 at 20:46
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/ dan - welcome to the site. I've edited out the thanks - we thank people here with votes (both up and down are thanks) and generally trim all the hello/thanks to cut right to the details - the founders call it a high signal to noise ratio. Please revert my edits if you would like that to be there :-) –  bmike Aug 10 '11 at 20:48
    
Please, what's the model identifier of your iMac? Make and model of graphics card? To view this information in Terminal, system_profiler SPHardwareDataType SPDisplaysDataType –  Graham Perrin Aug 17 '11 at 11:23
    
"non-default screen resolutions when using virtual display over screen sharing" — a statement, not a question. Please: do you prefer, or wish to avoid the non-default resolutions? –  Graham Perrin Aug 19 '11 at 7:13
    
Do you aim to work without margins/borders — scaling plus stretching to compensate for a difference in aspect ratios? Or, are a pair of margins (top+bottom or left+right) acceptable? –  Graham Perrin Aug 19 '11 at 7:20

3 Answers 3

up vote 1 down vote accepted

After half a year and 2 bounties, no-one genuine solution, so the answer appears to be a simple "You can't do that".

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According to MacTracker, your iMac9,1 supports two aspect ratios, both of which differ from the (approximate) 16:9 that is native to your MacBook Air:

  • 16:10 (1920 x 1200, 1600 x 1000, 1344 x 840, 1280 x 800, 1024 x 640, 800 x 500)

  • 4:3 (1600 x 1200, 1344 x 1008, 1280 x 960, 1024 x 768, 960 x 600, 800 x 600, 640 x 480).

Neither Remote Desktop 3.5 (460.87) nor Screen Sharing 1.3 (460044000000000) in Mac OS X 10.7.1 supports scaling to accommodate the different ratios.

JollysFastVNC

screenshot of the 'Correct Aspect Ratio' option in JollysFastVNC enter image description here

Without Correct Aspect Ratio and with Fullscreen, the display of a remote computer with a different ratio will be stretched to fill the display of the local computer.

Hopefully visible in the following screenshot, the horizontal stretch of a 1024 x 768 (4:3) display to fill my 1920 x 1200 (16:10) MacBookPro5,2:

screenshot of a stretched display

Alternatives

This is not a shopping recommendation. There may be alternatives to JollysFastVNC that support full screen and stretching.

Full screen Screen Sharing in Lion (suggested by bmike) is very tidy, if you can accept the linen margin.

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The 16:10 ratio seems best, with options of 1344 x 840 or 1280 x 800 being closest to my native 1366 x 768. But even though the iMac supports these resolutions, the options I have on the Virtual Display are 1920 x 1200, 1680 x 1050, 1280 x 1024 or 1024 x 768. Of these the first 2 are the close aspect ratio, but both are too large and leave everything looking too small when scaled to fit. I can choose from a wider range when using the hardware display, but this affects the iMac locally which I am trying to avoid as I then have to reset it after use. –  stuffe Aug 18 '11 at 23:32
    
1920 x 1200 on the virtual display sounds like you're at the MacBook Air, with a view of the remote iMac. The answer is for the opposite: an iMac view of the remote MacBook Air — "sharing (the screen,) from the Air to the iMac". Is the question misunderstood? –  Graham Perrin Aug 19 '11 at 6:48

Have you tried SwitchResX (http://www.macupdate.com/app/mac/8355/switchresx)? It looks interesting, though I haven’t gotten it to do what I need yet. (After Virtual Display stopped working, I attached a second secondary screen to my main machine, and am trying to set its resolution to match that of the remote screen.)

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