A text I read on grinding your own telescope mirror made the following point. A well equipped professional optical shop will know when they have achieved the minimum to meet their standards and will quite sensibly stop at that point. A gifted amateur may very well achieve more accurate results with a lot more effort, quite simply because they don't know when to stop. The same logic may well apply to early manual versus modern automated production. My 2c. Laurence Cuffe --- Rollei List - Post to rollei_list@xxxxxxxxxxxxx - Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe' in the subject field OR by logging into www.freelists.org - Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with 'unsubscribe' in the subject field OR by logging into www.freelists.org - Online, searchable archives are available at //www.freelists.org/archives/rollei_list