Prime Focus or Eyepiece projection

This image was taken last month with a sony video camera at prime focus. In an attempt to do better I decided to try the eyeypiece projection method and was completely unsuccesful.
My scope has a long focal length of 2650 mm @F15 and I wonder why one method seems so much more effective than the other? I much prefer the prime focus method illustrated here..but would love to hear suggestions from people who have experience with both successfully. And what lens worked better than others.

John

Attached Image:

John,

it is an issue of what magnification you want and what your
imaging system can handle (i.e. shutter speed).

there is a simple formula for the amplification of your
prime focus using (positive) eyepiece projection:

A = D/f - 1

where D is the distance from the eyepiece to the focal
plane of your camera, and f is the eyepiece focal length.
Multiply A by the focal length of your telescope and you
will get the resulting focal length. Note that the
exposure time goes up dramatically with your resulting f-ratio which is simply the overall focal length divided
by the aperature of your scope. The longer exposure time
leads to a poorer image quality due to the effects of
the atmosphere.

You can also use a barlow to magnify the image (this is
actually negative projection and the formula is a bit
different -- but probably close to what your barlow is
2x, 3x etc)

Hope this helps,

Joe