This is an original spherometer made by the world famous telescope and instrument maker &quot;Horace Dall&quot; sitting on a 4.25 inch Pyrex telescope mirror blank.

I obtained this device directly from a former telescope maker in England and have all documentation on this including letters from Mr.Dall himself!

Horace Dall is the co-inventor of the Dall-Kirkham Cassegrain Telescope. Also pictured is a 6 inch optical flat used for referencing the dial indicator on the spherometer.

Al Paslow telescope collection.