Calculating aperture

I have a nice Pentax-A 50mm f1.7. As well as using this as is I also combine it with a really useful 2x Macro converter. This gives me both a 100mm Macro lens and 100mm telephoto. My question is what would be the max aperture with the converter assuming a loss of 2x f stops. Is there a table somewhere of "standard" apertures etc
Cheers
Donut

Donut - is this what you want?

Should be everything you need there on Wikipedia

f/1.7 is a half-stop, so two stops smaller takes you to f/3.3

Hope that helps!
Matt

Apertures run in the following order (largest to smallest):

f1
f1.4
f2
f2.8
f4
f5.6
f8
f11
f16
f22
f32

Each one lets in exactly half as much light as the one preceding it. Lenses like you 50/1.7 have a maximum aperture that is effectively f1.4-and-a-half. Add two stops to that will give you something like f3.5 (which is effectively f2.8-and-a-half).

Hope that helps!

Quick Fingers Matt beat me to it!

Thanks that's exactly what I wanted