What power Barlow with a webcam?

I've just bought a 5x GSO APO barlow - probably never get a chance to use it given the seeing conditions here, but if we do get a good night then at least I'll have it in my bag and a chance to get a vgood pic of Jupiter or Saturn close up - or some really close up crater detail on luna.

So with my 12in 1500FL scope and 3 barlows 2x, 3x, 5x. that gives me FL of 3000, 4500 and 7500 to enter into the calculator on Johns link.

So I need to use the 5x to get in the .1-.2 arc sec/pixel range. have I got that right??

Correct a 5x barlow on your scope with a 5.6 micron pixel size will give you (5.6/5*1500)*206.3=0.15 arcsec per pixel which would be right in there.
HOWEVER......we rarely get seeing conditions that will allow that kind of amplification successfully. I normally stick to my 2x Ultima APO barlow for webcam imaging.

Keith,

Yes, that is correct. However, please note that once you know the image scale for one barlow (ex. 2x), the others can be computed immediately since they affect the effective focal length in a linear fashion.

In other words, the 5x barlow increases the effective focal length by a further 2.5 times relative to the 2x barlow. Therefore, if you have the image scale with the 2x barlow, take that figure and divide it by 2.5 to get the image scale when using the 5x barlow. Proceed in a similar fashion for the 3x barlow ... and any other barlow you care about.

Thanks, there's some useful info there. One thing I've found from the web is that 6mm is the focal length of the Toucam's lens and 4.5mm is the SPC900NC lens focal length. But the lens is removed for astronomical use, so my original calculations don't hold.

Using the equation John gave, it looks like I can use a 3x Barlow. But first I've got to get up the nerve to modify the camera.

Thanks,
Noel