I've got a Bronica SQ-A and an 80mm f/2.8. I have no problem with the lens except the distance I must maintain from my subject. Now I'm not looking to do true macro work, just get a little closer to my subject than I can now.

I really have got it down to 2 options: 110mm f/4.5 or get an 18mm extension tube and use my 80 f/2.8. I'm wondering what the effective f/ would be if I got the 18mm extension tube? If it's around 4.5, and there are no other sirious issues in terms of quality when using an extension tube, then I'll probably go with that just to reduce cost.

Any opinion is welcome and appreciated