Most (Edit: Okay, many) SCSI scanners were 25-pin. Don't ask me, but Macs also had 25-pin SCSI connectors. Regardless, you can go buy a cable that'll work just fine. You might have termination issues, though. Do you have other external SCSI devices? If not, then you should be okay. If you do, I'd suggest seeing if you can find a 50-to-25 pin adapter (I don't know that these exist (Edit: I just checked, and they do, although they're pretty pricy)) and placing the scanner not at the end.