title: How to fix error: 'Microsoft.Devices.PhotoCamera' does not contain a definition for 'IsFocusAtPointSupported' ... in windows phone 7.1 application
body: <p>I'm doing application about camera focus in Windows Phone 7.1 </p>
  
  <p>I referenced <a href="http://msdn.microsoft.com/en-us/library/microsoft.devices.photocamera(v=vs.92).aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/microsoft.devices.photocamera(v=vs.92).aspx</a> and added assembly:  Microsoft.Phone to my project reference but I get this error : 'Microsoft.Devices.PhotoCamera' does not contain a definition for 'IsFocusAtPointSupported' and no extension method 'IsFocusAtPointSupported' accepting a first argument of type 'Microsoft.Devices.PhotoCamera' could be found (are you missing a using directive or an assembly reference?).</p>
  
  <p>I intalled:<br>
  Microsoft Visual C# 2010,<br>
  Microsoft Windows Phone Developer Tools 7.1 (Beta) - ENU,<br>
  Microsoft Visual Studio 2010 Ultimate - ENU Service Pack 1.</p>
  
  <p>Thanks for any idea.</p>