There are two direct approaches to this task. The first uses the DiskUtility GUI, the other uses the Terminal app.

DiskUtility GUI Approach

1. Insert CD or DVD into your Mac
2. In Finder, Go to the Utilities Folder and launch Disk Utility
3. Click to high-light the mounted "DISC", Unmount it.
4. Click New Image, Saving it to your Desktop
4a. Make Sure it is Uncompressed and Not Encrypted
5. Once Finished, you still need to launch the Terminal App
6. In Terminal type: cd ~/Desktop
7. hdiutil makehybrid -iso -joliet -o Master.iso Master.cdr
7a. Replace "Master" with the name of the .cdr file you made in step 4.

Terminal App Approach

1. Insert CD or DVD into your Mac
2. In Finder, Go to the Utilities Folder and launch Terminal
3. Type in these commands in the terminal window:

 [prompt]$ drutil status
 Vendor   Product           Rev 
 MATSHITA DVD-R   UJ-868    KB19
 
           Type: DVD-ROM              Name: /dev/disk2
       Sessions: 1                  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:  843:28:64         blocks:  3795664 /   7.77GB /   7.24GiB
    Writability: 
      Book Type: DVD-ROM (v1)

Notice the "Name" you need it for the next command:

 [prompt]$ diskutil unmountDisk disk2
 [prompt]$ dd if=/dev/disk1 of=file.iso
 [prompt]$ diskutil mountDisk disk2