You also might want to consider this by Astro Physics:
http://www.astro-physics.com/index.h...ducts/products
Reasonably priced and certainly does a fine job. I took these images of M83 and M16 using this product and my TEC140:
http://www.pbase.com/prejto/image/152287993
http://www.pbase.com/prejto/image/152783100
As for the Televue products I've usually just seen these used for planetary photography. For DS targets you might be better off with a specialised product. For DS targets I can't imagine you would want to use a 4x barlow. Once you push your scope to near f14 you will pay a big price both in guiding difficulties and image capture times. 1.5-1.8 seems a quite decent range to operate in.
Peter
Peter