I'm thinking of getting the Sea & Sea housing for my 40D

I already own the 60 mm Macro and the 10-20 Sigma.

I'm just not sure of which dome I should get for the Sigma. As the chart from S&S suggests, I can go for either the compact dome or the NX fisheye one (I excluded the glass one for several reasons)

A future lens would be the Tokina 10-17, would that lens work in the compact dome?

Do I need a extension for the Fisheye dome or does it connect directly to the housing?

Sorry for all the questions...but it's a bit confusing

Can I ask what are the reasons for the exclusion of the Optical Dome Port?
It is a GREAT port for the Tokina 10-17...
All NX Ports (including all the domes you mentioned) need the "large" adapter.
And for the Sigma 10-20 you will probably need another Extension Ring, I think in your case the SX Extension Ring is better, but not 100% sure.
Also not sure if you will be able to access the zoom on those lenses, I have no RDX housing closing to me for the testing.
Anyone knows that?

You're going to love the S&S for the 40D, the 10-17 works very well with the SX extention(short one) and the NX Fisheye dome port. Sorry can't help you with the compact dome question.

Good Luck!
Steve

The main reqson being the price...

By looking at the system chart, it seems like you don't need any subport for the big Fisheye dome. Maybe you need the adapter for the RDX housings...

Does anyone know if you need an adapter or not?

/Erik

All RDX housings use a new port system.
NX Ports like the domes do need an adapter:
- RDX Port Base L Product No. 30109

The other adapter (RDX Port Base S) is for the Compact Ports, like the Compact Macro Ports and the CX Compact Dome Port.
Those lenses are not in the Compatibility Chart for the RDX housings.
My guess would be to use it as in the MDX Charts with the Base L adapter, but you might loose the zoom ring... this gotta be tested.
Do you have a S&S dealer close to you?

Good luck.