Nice image of the Moon Prova
My understanding is that the afocal technique is where you just put the camera with lens attached up to the telescope eyepiece.
The technique you describe where there is no camera lens or telescope eyepiece involved is called prime focus.
I'm no expert at this but M42 is comparable in size to the Moon so the image scale you have at prime focus seems good to me.
You will need to play with the manual mode on your D50 until you can work out how to take exposures that are seconds long. On my D80 it is rotating the main command dial that does this.
My limited attempts at prime focus deep space imaging have highlighted the need for careful attention to accurate polar alignment and focus. You do have the EQ5 though so you are in a much better position than me for both of these.
Sorry I've yet to suceed on M42 myself so there's not much more I can say.