Quote Originally Posted by bdial View Post
It's probably a projection petzval. Given the size and weight, it probably has a pretty long focal length, and possibly enough coverage for 8x10 or bigger, as a guess.
Point the lens out a window with a piece of white card behind it, move the card or lens until you get a focused image to estimate the focal length and image circle.
Once you know the focal length you can calculate the lens's speed.

One of the Mods here had a great how-to video for this, but it's not showing up for me in searches.

Thanks, I'll try that out this week