From .NET, you access these properties from the Reader Class as:
        ReaderParameters.ReaderSpecific.ImagerSpecific This is equivalent to the IMAGER_SPECIFIC structure for setting the Imager Specific parameters in C++.  While it should be in earlier versions of the EMDK for .NET, I'm using version 2.3 at the moment and this class can be found in the documentation under the Barcode Assembly. Dave Mohnke

There is no MKSeries namespace at EMDK2.3. So I'm still waiting for solution...

sorry.... i thought that you are using ver. 2.2
if you're using ver 2.3 you should write something like that:

MyReader.ReaderParameters.ReaderSpecific.ImagerSpecific.IlluminationMode = Symbol.Barcode.ILLUMINATION_MODE.ILLUMINATION_AUTO;

MyReader.ReaderParameters.ReaderSpecific.ImagerSpecific.AimMode =Symbol.Barcode.AIM_MODE.AIM_MODE_RETICLE

focus mode:
               MyReader.ReaderParameters.ReaderSpecific.ImagerSpecific.FocusMode =Symbol.Barcode.FOCUS_MODE.FOCUS_MODE_FIXED
MyReader.ReaderParameters.ReaderSpecific.ImagerSpecific.FocusPosition =Symbol.Barcode.FOCUS_POSITION.FOCUS_POSITION_FAR
MyReader.ReaderParameters.ReaderSpecific.ImagerSpecific.FocusPosition =Symbol.Barcode.FOCUS_POSITION.FOCUS_POSITION_NEAR

if you want to start scanning, write something like this: 
MyReader.Actions.ToggleSoftTrigger()

I have the same problem, any one can help me?

you have to use Symbol.MKSeries assembly....

....

private Symbol.MKSeries.Platform platform = new Symbol.MKSeries.Platform();

private Barcode.Barcode barcode1;

.........

For activating scaner:

            platform.ReaderParams.ContinuousTrigger = true;
            barcode1.EnableScanner = true;

For deactivating scaner:

            barcode1.EnableScanner = false;
            platform.ReaderParams.ContinuousTrigger = false;
            platform.Dispose();

.....