Here are 2 solutions. One is very expensive ($793!)but looks very interesting:
Follow links from here:
http://www.astro-physics.com/index.h...ducts/products
Baader Fluorite Flatfield Converter Barlow (BPFFC)
or
2" Advanced Convertible Barlow (BARADV) ($250)
I've used the 2" AP barlow with my KAF8300 CCD and it works very well. You can adjust the power somewhat by moving in/out. I took this photo of M83 using it with my TEC140:
http://www.pbase.com/prejto/image/152287993
and M16
http://www.pbase.com/prejto/image/149151685
TAK also has a good photographic barlow at 1.6X.
I would think you need 2" to avoid vignetting. Personally I'd go with one of these over your standard barlows.
Peter