I have a 3.8 Ultrascopic as my shortest focal length. I have used it with a 2x TV Big Barlow for 802x (64x per inch) on my 12.5 with good results, but not what I would use everynight for sure. With a DOB this is chasing the rabbit for sure! 
I have also uses 802x (53x per inch) in my 15" before with good images, not perfect, but good.
Floyd
I have also uses 802x (53x per inch) in my 15" before with good images, not perfect, but good.
Floyd
[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue
Amateur Imager
