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The ED-2s are reported to be very fussy about eye placement, blacking-out if if you don't keep your eye positioned just right.
Unless you have an astigmatism, try removing your glasses for viewing. Also, at higher powers the resulting smaller exit pupils may fall inside of the astigmatic portion of your eye. Remember:
EPmm = Dmm / Magnification;
where EP is exit pupil in mms
D is the objective diameter (again in mms)
Magnification is the effective focal length of the objective divided into
the focal length of the eyepiece.
300x in your 300D scope produces a 1mm EP, which may not be effected by an astigmatism.
Another trick for those needing long eye relief is to get to high powers by barlowing longer FL eyepieces. A barlow changes the effective focal length of the telescope not the eyepiece, so the eyepiece retains it's eye relief when barlowed. Ex. - a typical plossl has eye relief = ~.75xFL, so a 15mm eyepiece with a 3x barlow results in the same 300x (in your scope) as a 5mm eyepiece, but with longer eye relief (11.25mm vs. 3.75mm).
In general, I think the new owner of a fast dob (< f/5) should buy a few stop-gap eyepieces to tide you over until you invest in some quality wide-field eyepieces. Celstron Ultimas, Orion Ultrascopics or Orion Highlights (not sure what equivalents you have down under) should do just fine. Avoid the bargain wide-fields - You're gonna end up replacing them. JMHO
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