Find out in what /dev is your cd-rom:

drutil status

Vendor Product Rev
MATSHITA DVD-R UJ-825 DAM5

Type: CD-ROM Name: /dev/disk1
Cur Write: 16x CD Sessions: 1
Max Write: 16x CD Tracks: 3
Overwritable: 00:00:00 blocks: 0 / 0.00MB / 0.00MiB
Space Free: 00:00:00 blocks: 0 / 0.00MB / 0.00MiB
Space Used: 66:55:27 blocks: 301152 / 616.76MB / 588.19MiB
Writability: 

So /dev/disk1 is or cd-rom now to make the ISO just run:

dd if=/dev/disk1 of=file.iso