1. Insert CD/DVD source

2. Fire up a Terminal, you can then determine the device that is you CD/DVD drive using the following command:

$ drutil status
Vendor Product Rev
MATsh*tA DVD-R UJ-835E GAND

Type: DVD-ROM Name: /dev/disk1
Cur Write: 8x DVD Sessions: 1
Max Write: 8x DVD Tracks: 1
Overwritable: 00:00:00 blocks: 0 / 0.00MB / 0.00MiB
Space Free: 00:00:00 blocks: 0 / 0.00MB / 0.00MiB
Space Used: 364:08:27 blocks: 1638627 / 3.36GB / 3.13GiB
Writability: 
Book Type: DVD-ROM

3. Umount the disk with the following command:
$ diskutil unmountDisk /dev/disk1
Disk /dev/disk1 unmounted

4. Create the ISO file with the dd utility (may take some time):
$ dd if=/dev/disk1 of=file.iso bs=2048

5. Test the ISO image by mounting the new file (or open with Finder):
$ hdid file.iso

6. The ISO image can then be burnt to a blank CD/DVD.