Eyepiece Focal Plane Data?

[sheeny]

Does anyone have any data on the focal plane positions of any of the following eyepieces? i.e. mm either side of the shoulder of the EP.

Televue 13mm Type 6 Nagler
Celestron 25mm E-Lux Plossl
Celestron 32mm plossl
Celestron 15mm plossl
Celestron 9mm plossl

I've read ways to measure the position of the focal plane using a telescopic focusser but I don't have that type of focusser on either my C8 or my PST. Are there other methods I could use?

I'm interested in starting to play about with EP projection, but I'd like to be able to calculate what magnification I manage to achieve.

Thanks,

Al.