barlow advice

[Harpspitfire]

ive checked out some optical design sites- ive noticed on my scope when using a 2" focuser over a 1.25, the 2" slightly increases the f/l, naturally changing the f/r a bit- but my ultima 2X barlow works fine either way, as far i can understand the focus point changed a little but the optical train is still intact- ive seen those tele-extenders like orions sales but never bought one- anyway- i made my own extension around 2", but never seemed quite to get a good image this way, after reading further i found a barlow is supposedly matched to the optical system, so a 2X barlow SHOULD be used as a 2X barlow, aside from the usual issues, ive read it induces spherical abberation when trying to extend it, spherical abberation sucks when your trying to planetary image, so according to this, im stuck at 2X with no modications-- any opinions on this?- i guess my only option is a 2.5 powermate if i want to increase the F/l- are they really that good?--on the poor mans side, ive noticed OPT has a 2.5X, 3 element APO optical glass, FMC for under $50 , that sounds like a good deal if its performs well- 'or' i could go back to using a 1.25 diagonal and use the barlow 1st- hoping turbulance will support that '3x mode'- john :shrug:
http://www.optcorp.com/product.aspx?pid=30-114-115-10864 (http://www.optcorp.com/product.aspx?pid=30-114-115-10864)